Over the first two years of the COVID-19 pandemic, the coronavirus directly or indirectly killed about 15 million people worldwide, according to estimates from the World Health Organization. In the United States, more people died in 2020 and 2021 than during the 1918 influenza pandemic, which was widely called the most deadly in recorded history. 

The word “deadly” certainly applies to the virus that causes COVID-19. And yet, epidemiologists hesitate to give SARS-CoV-2 the superlative of deadliest virus in human history. To them, the raw number of mortalities caused by a given virus doesn’t always paint the full picture of a pathogen’s danger—especially when comparing viral outbreaks across time.

Raw mortality numbers have to be taken in the context of the world’s total population, says Jennifer Nuzzo, professor of epidemiology and director of the Pandemic Center at Brown University School of Public Health. “A lot of people talk about how COVID deaths eclipsed what we saw in 1918,” she says. “It’s really important to remember that the population of 1918 was a fraction of what it is today.” In that context, the flu of 1918 rises back up in the ranks in terms of deadliness.

Using the “case fatality rate” metric to determine what virus is the deadliest, rabies would likely come out on top. That’s because, if an infection becomes symptomatic, rabies is fatal to humans in more than 99 percent of cases. Globally, approximately 59,000 people die from rabies every year. Very few of those deaths—an average of two in the US—occur in the developed world because of rabies vaccines for household pets and swift medical interventions after bites.

But “a virus doesn’t have to have a very high case fatality ratio to cause a tremendous amount of death and disruption,” Nuzzo says. “It’s more about looking at the environments in which the viruses are spreading, and our social and human vulnerabilities to it.” 

A virus with a lower case fatality rate can kill more people if it’s highly transmissible, with a long period of time before severe or obvious symptoms set in. This allows an infected person to expose many others. That’s why SARS-CoV-2 caused such a rapid and devastating outbreak around the globe. It’s easily transmitted via airborne droplets, and doesn’t always or immediately cause severe illness. 

[Related: Can viruses be good for us?]

Globalization sped it along, too. “When a virus spreads at the pace of a human being walking, that’s very different than when you can hop on an airplane and be anywhere in the world in 36 hours,” Nuzzo says. 

During large outbreaks such as epidemics or pandemics, epidemiologists look at another metric, called excess deaths: how many more people died during a period of time than typically do over that same window. Excess deaths can account for other indirect ways that a virus causes death, Nuzzo says, such as patients who need critical care but can’t get it in overburdened hospitals.

Here’s how some of the most devastating viruses in human history tell different stories of how high a death toll can rise:

Influenza

The 1918 influenza pandemic still far and away ranks as the deadliest global outbreak of the 20th century. Thought to be caused by an H1N1 virus, it spread globally in 1918 and 1919. An estimated 500 million people were infected (approximately a third of the global population) and 50 million people died worldwide, about 675,000 of whom were in the United States, according to the Centers for Disease Control and Prevention. 

Without sophisticated testing and tracking, death toll estimates rely heavily on excess death calculations. Some suggest the true toll was closer to 17 million, while others set it much higher at 100 million. William Schaffner, professor of preventive medicine and professor of medicine in the division of infectious diseases at the Vanderbilt University School of Medicine, cautions against over-interpreting comparisons between the historic flu data and modern viral outbreaks.

[Related: Can you get diseases from bad bathroom smells?]

 “We are determining cases and even counting deaths with much more precision now than we did then,” he says. At the time, there were also no flu vaccines and no antibiotics to treat secondary bacterial infections, which likely drove the excess death toll higher.

Today, the youngest and oldest people are most likely to die from influenza. But during the pandemic over 100 years ago, Schaffner says, deaths bore a different signature: mortality peaked among young and middle-aged adults, too. Why that happened is still unclear, he says, but it contributed to the historic toll of that pandemic.

Influenza continues to hold its place as one of the deadliest viruses, despite the availability of vaccines. Variants of the influenza virus have led to other pandemic-level events, such as the 2009 outbreak colloquially called the swine flu pandemic. But the virus is also endemic in our society, and infects an estimated 1 billion people globally every year, according to the World Health Organization. Of those cases, the WHO reported in 2019, somewhere between 290,000 to 650,000 result directly or indirectly in deaths. 

An estimated 40.1 million people have died from AIDS-related illnesses since the start of the epidemic, according to the Joint United Nations Program on HIV and AIDS. That is nearly half of the number of people estimated to have become infected with HIV since the start of the epidemic, at an estimated 84.2 million. 

The case fatality rate of HIV/AIDS was historically quite high. Some estimates put it around 80 percent without treatment. But much has changed since the 1980s. Today, there are ways to manage HIV and mitigate the immunodeficiencies associated with an infection, and most patients are diagnosed sooner after an infection. In the United States, the rate of HIV-related deaths fell by nearly half from 2010 to 2017, according to the CDC. 

That excess deaths metric likely reached a much higher number by the time officials declared the public health emergency over in early May. The Omicron wave that swept around the globe in late 2021 and early 2022 saw one of the largest surges in cases of COVID-19 and, although the variant didn’t seem to be more deadly than previous variants, with millions of people infected, a high death toll in the hundreds of thousands was inevitable. 

Early in the pandemic, the case fatality rates calculated for SARS-Cov-2 varied considerably. Many estimates were likely higher than the true number, as researchers scrambled to devise tests for the virus and milder cases slipped through the cracks. In early 2020, estimates of the case fatality rate by country ranged as high as 25 percent or more. Since then, case fatality rates have dropped, and now, according to Johns Hopkins University, they are as high as 4.9 percent. In the US, the case fatality rate is 1.1 percent. 

Mortalities continued to stack up into the 20th century, with an average of three out of every 10 people infected dying. The disease, which is caused by variola virus, is estimated to have killed more than 300 million people from 1900, until a global vaccination campaign halted its path of devastation in 1977. It was the first disease ever to be eradicated. 

[Related: The first honeybee vaccine could protect the entire hive, starting with the queen]

But it was the very thing that made it particularly fearsome that was its downfall, Schaffner says. “It created such a distinctive rash that people could identify it and fear it. And that was one of its Achilles heels,” he says. Because it was so easily identifiable, and spread so slowly, vaccinating the local population near an outbreak swiftly curtailed transmission. Such an approach, he says, was part of the vaccination strategy that eradicated the great pestilence. 

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On a clear, moonless night, you might be able to see thousands of stars sparkling like jewels above. But a keen eye will notice that they don’t all look alike. Some glow brighter than others, and some display warm red hues.

In the beginning…

All stars form from a cloud of dust and gas when turbulence pushes enough of that material together, pressed into one body by gravity. As that clump collapses in on itself, it starts to spin. The material in the middle heats up, forming a dense core known as a protostar. Gravity draws even more material toward the developing star as it spins, making it bigger and bigger. Some of that stuff may eventually form planets, asteroids, and comets in orbit around the new star.

The stellar body remains in the protostar phase as long as material still collapses inward and the object can grow. This process can take hundreds of thousands of years.

The amount of mass that is gathered during that stellar formation process determines the ultimate trajectory of the star’s life—and what types of stars it will become throughout its existence.

Protostars, baby stars—and failures

As a protostar amasses more and more gas and dust, its spinning core gets hotter and hotter. Once it accumulates enough mass and reaches millions of degrees, nuclear fusion begins in the core. A star is born.

For this to occur, a protostar has to accumulate more than 0.08 times the mass of our sun. Anything less and there won’t be enough gravitational pressure on the protostar to trigger nuclear fusion. 

Those failed stars are called brown dwarfs, and they remain in that state for their lifetime, progressively cooling down without nuclear fusion to help release new energy. Despite their name, brown dwarfs can be orange, red, or black due to their cool temperatures. They tend to be slightly larger than Jupiter, but are much more dense.

Protostars that do acquire enough mass to become a star sometimes go through an interim phase. During a roughly 10 million-year period, these young stars collapse under the pressure of gravity, which heats up their cores and sets off nuclear fusion. 

In this stage, a star can fall into two categories: If it has a mass two times that of our sun, it is considered a T Tauri star. If it has two to eight solar masses, it’s a Herbig Ae/Be star. The most massive stars skip this early stage, because they contract too quickly. 

Once a sufficiently massive star begins to undergo nuclear fusion, a balancing act begins. Gravity still exerts an inward force on the newborn star, but nuclear fusion releases outward energy. For as long as those forces balance each other out, the star exists in its main sequence stage. 

Fueling main sequence stars

Main sequence stars, which can last for millions to billions of years, are the vast majority of stars in the universe—and what we can see unaided on dark, clear nights. These stars burn hydrogen gas as fuel for nuclear fusion. Under the super-hot conditions in the core of a star, colliding hydrogen fuses, generating energy. This process produces the chemical ingredients for a reaction that makes helium. 

Mass dictates what type of star an object will be during the main sequence stage. The more mass a star has, the stronger the force of gravity pushing inward on the core and therefore the hotter the star gets. With more heat, there is faster fusion and that generates more outward pressure against the inward gravitational force. That makes the star appear brighter, bigger, hotter, and bluer.

[Related: The Milky Way’s oldest star is a white-hot pyre of dead planets]

Many main sequence stars are also often referred to as “dwarf” stars. They can range greatly in luminosity, color, and size, from a tenth to 200 times the sun’s mass. The biggest stars are blue stars, and they are particularly hot and bright. In the middle are yellow stars, which includes our sun. Somewhat smaller are orange stars, and the smallest, coolest stars are red stars. 

The hottest stars are O stars, with surface temperatures over 25,000 Kelvin. Then there are B stars (10,000 to 25,000K), A stars (7,500 to 10,000K), F stars (6,000 to 7,500K), G stars (5,000 to 6,000K—our sun, with a surface temperature around 5,800K is one of these), K stars (3,500 to 5,000K), and M stars (less than 3,500K). 

Upsetting the balance to grow a giant star

As a star runs out of fuel, its core contracts and heats up even more. This makes the remaining hydrogen fuse even faster: It produces extra energy, which radiates outward and pushes more forcefully against the inward force of gravity, causing the outer layers of the star to expand.

As those layers spread out, they cool down, and that makes the star appear redder. The result is either a red giant or a red supergiant, depending on if it’s a low mass star (less than 8 solar masses) or a high mass star (greater than 8 solar masses). This phase typically lasts up to around a billion years.

Appearing more orange than red, some red giants are visible to the naked eye, such as Gamma Crucis in the southern constellation Crux (aka the Southern Cross).

The death and afterlife of a low-mass star

Stars die in remarkably different ways, depending on their masses. For a low-mass star, once all the hydrogen is nearly gone, the core contracts even more, getting even hotter. It becomes so scorching that the star can even fuse helium—which, because it’s an element heavier than hydrogen, requires more heat and pressure for nuclear fusion. 

As a red giant burns through its helium, producing carbon and other elements, it becomes unstable and begins to pulsate. Its outer layers are ejected and blow away into the interstellar medium. Eventually, when all of these layers have been shed, all that remains is the small, hot, dense core. That bare remnant is called a white dwarf.

[Related: Wiggly space waves show neutron stars on the edge of becoming black holes]

About the size of Earth, though hundreds of thousands of times more massive, a white dwarf no longer produces new heat of its own. It gradually cools over billions of years, emitting light that appears anywhere from blue white to red. These dense stellar remnants are too dim to see with a naked eye, but some are visible with a telescope in the southern constellation Musca. Van Maanen’s star, in the northern constellation Pisces, is also a white dwarf. 

The explosive stellar death of a high-mass star

Stars with mass eight times that of our sun typically follow a similar pattern, at least in the beginning of this phase. As the star runs low on helium, it contracts and heats up, which allows it to convert the resulting carbon into oxygen. That process repeats itself with the oxygen, converting it to neon, then the neon into silicon, and finally into iron. When no fuel remains for this fusion sequence, and energy is no longer being released outward from those reactions, the inward force of gravity quickly wins. 

Within a second, the outer layers of the star collapse inward. The core collapses and then rebounds, sending a shock wave through the rest of the star: a supernova. 

Life after a supernova for a star takes one of two paths. If the star had between eight and 20 times the sun’s mass during its main sequence stage, it will leave behind a superdense core called a neutron star. Neutron stars are even smaller in diameter than white dwarfs, at about the size of New York City’s length, and contain more mass than our sun.

But for the most massive stars, that remnant core will continue collapsing under the pressure of its own gravity. The result is a black hole, which can be as small as an atom but contain the mass of a supermassive star.

One such example is a star in a binary or multi-star system that accretes mass from a companion. With all that extra mass to burn, it can seem younger than its true age, appearing bluer and brighter. That, Gosnell says, is called a blue straggler star, because it seems to be “straggling behind its expected evolution.” 

Another odd type of star is sub-subgiant, Gosnell says. These stars also are found in binary systems, and are transitioning from the main sequence to the red giant branch, though they stay dimmer. This kind of subgiant star has “really active magnetic fields with lots of star spots on the surface,” she says. “And so you have these really magnetically active, visually dynamic stars as the star spots rotate in and out of view.” 

The ongoing ESA mission, she adds, is reviewing stars with a “much finer-toothed comb”—which may reveal the true variety and complexity of stars that have existed all along. As such missions “peel back the layers,” Gosnell says, “We start to see really interesting stories come out that challenge the edges of these categories.”

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Despite what Star Trek’s warp-speed journeys would have us believe, interplanetary travel is quite the hike. Take getting to Mars. Probes sent to the Red Planet by NASA and other space agencies spend about seven months in space before they arrive at their destination. A trip for humans would probably be longer—likely on the timescale of a few years. 

There are a lot of things that a human crew needs to survive that robots don’t, such as food, water, oxygen, and enough supplies for a return—the weight of which can slow down a spacecraft. With current technology, NASA calculations estimate a crewed mission to Mars and back, plus time on the surface, could take somewhere between two and three years. “Three years we know for sure is feasible,” says Michelle Rucker, who leads NASA’s Mars Architecture Team in the agency’s ​​Human Exploration and Operations Mission Directorate.

But NASA aims to shorten that timeline, in part because it would make a Mars mission safer for humans—we still don’t know how well the human body can withstand the environment of space for an extended period. (The record for most consecutive days in space is 437.) The agency is investing in projects to develop new propulsion technologies that might enable more expeditious space travel. 

A crooked path to Mars

In a science-fictional world, a spacecraft would blast off Earth and head directly to Mars. That trajectory would certainly make for a speedier trip. But real space travel is a lot more complicated than going from point A to point B.

“If you had all the thrust you want, you could ignore the fact that there happens to be gravity in our universe and just plow all the way through the solar system,” says Mason Peck, a professor of astronautics at Cornell University who served as NASA’s chief technologist from 2011 to 2013. “But that’s not a scenario that’s possible right now.”

Such a direct trajectory has several challenges. As a spacecraft lifts off Earth, it needs to escape the planet’s gravitational pull, which requires quite a bit of thrust. Then, in space, the force of gravity from Earth, Mars, and the sun pulls the spacecraft in different directions. When it is far enough away, it will settle into orbit around the sun. Bucking that gravity requires fuel-intensive maneuvers.

[Related: Signs of past chemical reactions detected on Mars]

The second challenge is that the planets do not stay in a fixed place. They orbit the sun, each at its own rate: Mars will not be at the same distance from Earth when the spacecraft launches as the Red Planet will be, say, seven months later. 

As such, the most fuel-efficient route to Mars follows an elliptical orbit around the sun, Peck says. Just one-way, that route covers hundreds of millions of miles and takes over half a year, at best. 

But designing a crewed mission to the Red Planet isn’t just about figuring out how fast a spacecraft can get there and back. It’s about “balance,” says Patrick Chai, in-space propulsion lead for NASA’s Mars Architecture Team. “There are a whole bunch of decisions we have to make in terms of how we optimize for certain things. Where do we trade performance for time?” Chai says. “If you just look at one single metric, you can end up making decisions that are really great for that particular metric, but can be problematic in other areas.”

One major trade-off for speed has to do with how much stuff is on board. With current technology, every maneuver to shorten the trip to Mars requires more fuel. 

If you drive a car, you know that in order to accelerate the vehicle, you step on the gas. The same is true in a spacecraft, except that braking and turning also use fuel. To slow down, for instance, a spacecraft fires its thrusters in the opposite direction to its forward motion.

But there are no gas stations in space. More fuel means more mass on board. And more mass requires more fuel to propel that extra mass through the air… and so on. Trimming a round-trip mission down to two years is when this trade-off starts to become exponentially less efficient, Rucker says. At least, that’s with current technology.

New tech to speed up the trip

NASA would like to be able to significantly reduce that timeline. In 2018, the space agency requested proposals for technological systems that could enable small, uncrewed missions to fly from Earth to Mars in 45 days or less. 

At the time, the proposals didn’t gain much traction. But the challenge inspired engineers to design innovative propulsion systems that don’t yet exist. And now, NASA has begun to fund the development of leading contenders. In particular, the space agency has its eye on nuclear propulsion.

Spacecraft currently rely largely on chemical propulsion. “You basically take an oxidizer and a fuel, combine them, and they combust, and that generates heat. You accelerate that heated product through a nozzle to generate thrust,” explains NASA’s Chai. 

Engineers have known for decades that a nuclear-based system could generate more thrust using a significantly smaller amount of fuel than a chemical rocket. They just haven’t built one yet—though that might be about to change.

One of NASA’s nuclear investment projects aims to integrate a nuclear thermal engine into an experimental spacecraft. The Demonstration Rocket for Agile Cislunar Operations, or DRACO, program, is a collaboration with the Defense Advanced Research Projects Agency (DARPA), and aims to demonstrate the resulting technology as soon as 2027 .

[Related: Microbes could help us make rocket fuel on Mars]

The speediest trip to Mars might come from another project, however. This concept, the brainchild of researchers at the University of Florida and supported by a NASA grant, seeks to achieve what Chai calls the “holy grail” of nuclear propulsion: a combination system that pairs nuclear thermal propulsion with an electric kind. 

“We did some preliminary analysis, and it seems like we can get pretty close to [45 days],” says the leader of that project, Ryan Gosse, a professor of practice in the University of Florida’s in-house applied research program, Florida Applied Research in Engineering (FLARE). One caveat: That timeline is for a light payload and no humans on board. However, if the project is successful, the technology could potentially be scaled up in the future to support a crewed mission.

There are two types of nuclear propulsion, and both have their merits. Nuclear thermal propulsion, which uses heat, can generate a lot of thrust quickly from a small amount of fuel. Nuclear electric propulsion, which uses charged particles, is even more fuel-efficient but generates thrust much more slowly.

“While you’re in deep space, the electric propulsion is really great because you have all the time in the world to thrust. The efficiency, the miles per gallon, is far, far superior than the high-thrust,” Chai says. “But when you’re around planets, you want that oomph to get you out of the gravity well.”

The challenge, however, is that both technologies currently require different types of nuclear reactors, says Gosse. And that means two separate systems, which reduces the efficiency of having a nuclear propulsion system. So Gosse and his team are working to develop technology that can use the one system to generate both types of propulsion.

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When a spacecraft blasts off the surface of Earth, it eventually exits our planet’s airspace and enters outer space. Where, precisely, that boundary lies is up for some debate. 

“In science, the boundaries we draw don’t exist in nature exactly,” says Jonathan McDowell, an astrophysicist at the Center for Astrophysics | Harvard & Smithsonian. “Where a boundary exists is where some quantity changes very rapidly over a short distance… And that is true at this edge of the atmosphere. But what you choose to call space and what you choose to call Earth—that’s a human decision that’s not forced on us by physics.”

The implications of deciding where Earth ends and space begins go beyond whether or not travelers earn their astronaut wings. Air traffic is typically regulated on the national level, with countries controlling the airspace over their land. Flying too low, for example, has the potential to inadvertently start an international conflict. 

But “space is intrinsically global,” McDowell says. Different international treaties apply to space. As more nations launch satellites, and private spaceflight companies build a suborbital space tourism industry, defining the distinction between Earth’s airspace and outer space is becoming increasingly important. 

Physics behind the Kármán line

The Kármán line is based on physics, in that it describes how the characteristics of Earth’s atmosphere at different altitudes affect a craft’s ability to fly. Planes stay airborne largely from lift generated by their wings against the thickness of Earth’s atmosphere. But as our atmosphere rises in altitude, it thins. At a certain point, the air is too thin for traditional aircraft, and any craft above that altitude require a propulsion system, such as a rocket, to remain aloft. That distinction is the Kármán line.

The line is named for Theodore von Kármán, an engineer and physicist who was born in Hungary in 1881. He became a prominent expert in rockets during World War II, and co-founded the United States’ Jet Propulsion Laboratory. He is credited as being the first to calculate the altitude above which a craft would need to use a propulsion system to fly.

Von Kármán originally calculated the boundary to be roughly 50 miles above sea level. But, today, the Kármán line is commonly defined as an altitude of around 62 miles, or 100 kilometers. In fact, the agency that keeps track of standards and records in air and space, the Fédération Aéronautique Internationale, also uses this figure to define where space begins.

[Related: Where does outer space start?]

The thinking behind that round number of 100 kilometers, McDowell says, is that the boundary can’t be defined precisely because of the variability of the atmosphere. 

But McDowell wasn’t so sure that was the case. So he re-examined the history and calculations of the Kármán line in a paper published in the journal Acta Astronautica in 2018. He found that von Kármán’s original calculation was more accurate than previously thought, and with decades of advancement on atmospheric models, the variability is probably only within a few miles of the original 52 mile calculation. 

Is the Kármán line the only possible edge of space?

Some scientists have proposed other characteristics to define the boundary between Earth and space, such as the region in our planet’s orbit where a satellite breaks up upon reentry, McDowell says. “That, again, turns out to be in the 80s to 90s kilometers,” he says, which, in miles, is in the 50s.

Many US agencies, including the Federal Aviation Administration, typically use 50 miles as their boundary, too. The FAA and Air Force actually bestow astronaut wings on those who fly above an altitude of 50 miles. (However, not all passengers on a commercial flight will earn their wings, as in 2021 the FAA added criteria regarding a traveler’s contributions to a commercial space mission.)

But NASA Mission Control takes a different approach. Instead of focusing on aerodynamic lift, the space agency defines the point of reentry into Earth’s airspace from outer space as the place at which atmospheric drag becomes noticeable, at about 76 miles. 

There are other boundaries that some might consider for the edge of space, suggests McDowell. One is the Armstrong Limit, named for Harry G. Armstrong, an early American aerospace medicine physician, which is the altitude at which a human’s blood boils if they’re not protected from the low atmospheric pressure by a spacesuit, approximately 11 to 12 miles up. 

“You can play all kinds of games about what the criterion should be,” McDowell says. 

Another is more of a joke, McDowell says: The Ripley Line, which would be where nobody could hear you scream in space. “A very rough” calculation of the altitude of that boundary came out to a few hundred miles, he says, “but that could easily be totally wrong.”

Where is the edge of space on other planets?

This question of where a planet ends and space begins can be extrapolated to other worlds, McDowell says. A sort of Kármán line might exist on a world like Mars, because it also has an atmosphere (albeit a thinner one than Earth’s), he suggests. But the moon, for example, has no atmosphere. So does that mean it is entirely in space? Or is there a different kind of boundary, perhaps a gravitational one, that should be considered?

[Related: Jane Poynter wants to send you to the edge of space in a very big balloon]

“In the future, when we have, you know, Lunar City, and you’re taking off from Lunar City into orbit around the moon, at what point do you get handed over from local air traffic control to deep space traffic control?” he says. Or, “when do you have to consider the difference between a local flight or a local athlete jumping very high into lunar gravity, versus something that counts as space traffic?”

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How old is Earth? It may seem like a simple question to answer. The typical ballpark estimate is that our planet is around 4.5 billion years old. But the closer planetary scientists look, the squishier that story gets. Nuances about how our planet formed could shift the age of Earth by half a billion years or so. 

“An age is easy to talk about, but it becomes more and more complex as you zoom in,” says geology professor Thomas Lapen, who chairs the University of Houston’s Earth and atmospheric sciences department. As scientists have sought to determine more precise measurements of Earth’s age, they’ve had to grapple with the specifics of how our planet came to be.

“When you’re born, it’s an instant in time,” Lapen explains. But planetary formation is a process that takes millions of years. To assign an age to Earth, astrophysicists, planetary scientists, and geologists have to determine which point in the process could be considered Earth’s birth. 

When was Earth “born”?

About 4.6 billion years ago, gas and dust swirled in orbit around the newly formed sun. Over the first millions of years of the solar system, particles collided and merged into asteroids and the seeds of planets. Those space rocks kept smashing into one another, some growing larger and larger, shaping the solar system as we see it today. 

But planets aren’t simply big rock piles. As they amass material, these celestial bodies also differentiate into the layers of a core, mantle, and crust (at least in the case of Earth and the other terrestrial planets). Accretion and differentiation take time, likely on the order of tens of millions of years. Some might consider a point in that stage of Earth’s formation to be our planet’s birth. But Lapen says he thinks of it as Earth’s conception, and birth came later, when a cataclysmic event also formed the moon.

[Related: June 29 was Earth’s shortest day since the invention of atomic clocks]

According to the widely accepted giant impact theory, during the chaos of the early days of our solar system, the proto-Earth collided with another small body about the size of Mars. When the two slammed together, the debris coalesced into the moon in orbit around Earth. 

This impact also is thought to have essentially “reset” the materials that made up the planet, Lapen says. At the time, a thick magma ocean may have covered proto-Earth. Upon the powerful collision, the material of both bodies mixed together and coalesced into the planet and moon system we know today. Evidence for such a “reset” comes from both terrestrial and lunar rocks that contain identical forms of oxygen, Lapen explains. 

“Proto-Earth was, in all likelihood, destroyed or changed in composition,” Lapen says. “In my mind, the Earth wasn’t the Earth as we know it until the moon-forming event.”

If this event marked our planet’s birth, that would make Earth somewhere between 4.4 billion and 4.52 billion years old. But determining a more specific age for our planet requires sifting through ancient evidence. 

Assigning a number to our planet’s age

Like detectives searching for clues of an old crime, planetary scientists have to look at the evidence that remains today when piecing together our planet’s early history. But with all the turmoil during that chapter—the roiling magma ocean and intense geological turnover—the proof can be hard to find. 

One way to constrain the age of Earth is to search for the oldest rocks on the planet, Lapen explains, which formed right after the magma ocean hardened into a solid surface. For that date, scientists look to zircons discovered in the Jack Hills in Western Australia—the oldest known minerals. 

To determine the age of these crystals, a team of scientists used a technique called radiometric dating, which measures the uranium they contain. Because this radioactive element decays into lead at a known rate, scientists can calculate a mineral’s age based on the ratio of uranium to lead in the sample. This method revealed the zircons are approximately 4.4 billion years old.

These rocks suggest that the Earth-moon system must have formed sometime before 4.4 billion years ago, because the rock record “would be obliterated by the moon-forming event,” Lapen says. So the planet is no younger than 4.4 billion years old. But how much older could it be? To answer that, Lapen says, scientists turn elsewhere—including the moon.

[Related: Here’s how life on Earth might have formed out of thin air and water]

Rocks on the Earth’s satellite body are better preserved than the ones here, because the moon does not undergo processes like plate tectonics that would melt and reshuffle its surface. There are two main sources for these clues: in lunar meteorites that fall to Earth and in the samples collected directly from the moon during NASA’s Apollo program. 

Like proto-Earth, the young moon was also covered in a magma ocean. The oldest rocks taken from the lunar surface can indicate when the moon’s crust formed. Scientists have conducted radiometric dating on zircon fragments collected during the Apollo 14 mission, correcting the calculations for cosmic ray exposure, and determined that the lunar crust hardened approximately 4.51 billion years ago. 

There would have been a period of time between the collision and the bodies coalescing, cooling, and differentiating, Lapen says, so this date has a window of uncertainty, too, of about 50 million years. 

“Dating the exact event is very challenging,” he says. Lapen estimates the Earth-moon system likely formed between 4.51 billion and 4.52 billion years ago, but some scientists say calculations could be as many as 50 million years off.

Another way to constrain that window of time is to look at rocks that existed when the proto-Earth was forming. When the planets solidified from the debris around the young sun, not all of the material coalesced into the worlds and their moons we see today. Some remained preserved in asteroids or comets.

Sometimes those solar system time capsules come to us as meteorites that fall to our planet’s surface. The oldest known such space rock, Lapen says, is the meteorite Erg Chech 002. It is thought to be a fragment of an igneous crust of a primitive protoplanet from the early solar system. As such, dating the Erg Chech 002 meteorite provides a snapshot of a time when the proto-Earth was likely at a similar stage in its conception.

“If the ‘birth of the Earth’ is defined as the formation time of the first proto-Earth nucleus or protoplanet that ultimately grew through accretion to form the present-day Earth,” Lapen says, “then perhaps that was as long ago as the age of [Erg Chech 002].” Scientists calculated this chunk of igneous crust crystallized approximately 4.565 billion years ago.

Can Earth’s age be refined?

On human timescales, an uncertainty of 50 million years around when the Earth-moon system formed sounds vast and imprecise. But on planetary timescales, particularly billions of years ago, “it’s a good estimate,” Lapen says.

“The further back we look, oftentimes the less precise things are because of the gaps in the record. It’s a relatively short period of time, where a lot of things were happening—there was the impact, everything had to coalesce, and cool, and differentiate into sturdy rocky bodies that have a core, mantle, and crust,” he says.

However, scientists aren’t done. There is always the opportunity to get more precise and accurate measurements of Earth’s age, Lapen says, particularly as researchers obtain additional samples from the moon, meteorites, and asteroids.

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The sun roils with heat as thermonuclear reactions in its center produce high amounts of energy. Day to day, that energy is responsible for making Earth livable. But sometimes, solar flares can burst forth, sending highly energetic particles hurtling at top speeds into space. If our planet is in the radiation’s path, it can wreak havoc on our lives. 

[Related: What happens when the sun burns out?]

Although such consequences are rare, satellites and technology that relies on electricity and wireless networks are particularly vulnerable. In 1989, a geomagnetic storm set off by a powerful solar flare triggered a major blackout across Canada that left six million people without electricity for nine hours. In 2000, a solar eruption caused some satellites to short-circuit and led to radio blackout. In 2003, a series of solar eruptions caused power outages and disrupted air travel and satellite systems. And in February 2022, a geomagnetic storm destroyed at least 40 Starlink satellites just as they were being deployed, costing SpaceX more than $50 million.

What exactly are solar flares and solar storms?

Generally speaking, the term “solar storm” describes when an intense eruption of energy from the sun shoots into space and interacts with Earth. Charged particles constantly flow away from the sun into space in what is called the solar wind. But more significant eruptions can originate as solar flares, often from temporarily dark patches called sunspots, and intense explosions called coronal mass ejections. Any kind of variation in this activity can cause auroras. 

Solar flares are essentially flashes of light. They happen when strong solar magnetic fields protruding from the surface of the sun snap, releasing immense amounts of electromagnetic radiation at extremely high speeds. When that radiation slams into Earth, it injects energy into our planet’s ionosphere, the uppermost reaches of our atmosphere, explains Guhathakurta. The extreme ultraviolet radiation from the sun can polarize the particles in Earth’s ionosphere, she says, which can have cascading effects on any other charged particles in the vicinity—meaning anything that uses electricity is at risk.

And solar flares travel at the speed of light, says Jesse Woodroffe, who leads the space weather research program in NASA’s Heliophysics Division. That makes them difficult to anticipate and prepare for. “There is no way to get a signal to Earth faster than the solar flares, which are already traveling at the speed of light,” he notes. “So you have to predict the flare itself is going to happen. And that is a challenging science problem that we have not yet cracked.”

While solar flares are intense bursts of radiation, coronal mass ejections are explosions of energy particles. As such, they travel a bit slower. They occur when large portions of the outer atmosphere of the sun (the corona) explodes, sending superheated gas out into space. These “big blobs of solar material are ejected out at a very high speed, hundreds and hundreds of kilometers per second, but it is much slower than the speed of light,” Woodroffe adds. Those can take anywhere from half a day to three days to reach Earth, he says.

How to forecast space weather

Forecasting space weather isn’t quite like terrestrial weather forecasts. The big difference: On Earth, meteorologists have millions of measurements they can make and integrate into their predictive models. In space, Woodroffe says, there are just a few places scientists can put instruments to observe solar activity.

NASA shares the data from its solar observatories with the National Oceanic at Atmospheric Administration, which provides a probabilistic forecast of geomagnetic storm warnings and watches based on likelihood and geomagnetic intensity. Depending on how fast a solar storm is moving, they can send out warnings a few days before that space weather touches Earth, or just a couple of hours.

The ultimate goal, Woodroffe says, is to improve space weather forecasting to be on par with hurricane forecasting. His Earth-focused colleagues can predict where a hurricane might go by running different models, producing a range of outcomes within a high range of confidence, he says. “We are developing those sorts of capabilities for space weather.”

Are we seeing more solar flares?

So, back to those apocalyptic solar flare headlines. Is the sun really getting feistier and threatening the collapse of modern society each week? 

Space weather activity hasn’t changed recently, says Guhathakurta—but humanity has. In the past century, people have become increasingly reliant on electronics, and anything with an “on and off switch is vulnerable to solar storms,” she says. 

[Related: Make your own weather station with recycled materials]

When those energy particles come surging from the sun to Earth, the disturbance they cause in our planet’s magnetic field “creates electromagnetic fluctuation and voltage fluctuation, which can penetrate beneath the ground and create fluctuations on our electric power grid,” Guhathakurta says. And with growing dependence on devices that rely on orbiting satellite systems like GPS, our electronics are even more exposed to bursts of solar radiation.

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“There’s not actually a dinosaur constellation, right?” I asked aloud to no one as I peered up at the stars sparkling in the dark. 

Moments earlier I’d driven through the town of Dinosaur, Colorado. Now, as darkness settled around my car, I thought I spotted a sauropod in the stars through my driver’s side window. I chuckled to myself, feeling silly for seeing dinosaurs where there certainly were none, and chalked it up to the power of suggestion.

But, it turns out, I wasn’t just being silly. I was participating in a human tradition that extends back millennia, says Daniel Brown, associate professor in astronomy and science communication at Nottingham Trent University in England. The night sky, he says, is “an ideal canvas” for viewers to interpret and find visualizations of something that is relevant to their lives. “This is how we normally would start referring to constellations.”

But constellations aren’t just a sketch of every individual’s fanciful ideas. The way that the stars are splashed across the sky invites humans to see certain patterns. In fact, despite viewing the sky from distinct angles, many cultures around the world have identified groupings of stars in remarkably similar ways. Those parallels, and differences, offer a reflection of the astronomical dynamics playing out over the night sky, as well as the values and mindsets of the people who look up at it. 

One constellation, two stories

Constellations have long served as maps for navigation, canvases for storytelling, calendars for seasonal changes, and charts by which to impart knowledge and meaning. 

“Up until recently in human history, we didn’t have structured, written languages. Language was communicated orally,” says Duane Hamacher, associate professor of cultural astronomy at the University of Melbourne in Australia. “But the human brain evolved to be able to memorize enormous quantities of information. One of the ways that is done is through associating a memory to place, called the method of loci—which, he explains, includes the stars.

[Related: What would happen if the Milky Way died?]

By passing on knowledge of the constellations, deep cultural memories persist. Today, researchers have noticed a pattern: Many of the brightest stars are grouped together in strikingly similar constellations across cultures that historically had no known contact with each other. Western stargazers might know some of those star groupings as the Big Dipper, Orion, the Pleiades, and the Southern Cross.

These particular star groupings draw the eye with their brightness and proximity to each other in the night sky, attracting stargazers from both hemispheres, according to a team of researchers from the University of Melbourne. The researchers used a mathematical model to systematically group stars by their prominence and proximity, and compare those groupings against constellations from 27 different cultures around the world. This process tested what is considered a principle of how human visual perception works: The Gestalt law of proximity, which states that objects that are close together are perceived as unified groups, regardless of how different those objects may be individually. In a paper published earlier this year in the journal Psychological Science, the University of Melbourne experts found that those perception principles likely explain why so many different cultures have grouped the same stars together into constellations.

But the similarities don’t stop at which stars people visually group together. Humans have often mapped familiar images and stories over those pinpricks of light. And even those stories are often strikingly similar, despite being influenced more by cultural context than the characteristics of the stars themselves. 

For example, says Hamacher, who is an author on the Psychological Science paper, the male figure of Orion is often seen as a man or men pursuing a group of girls or women, whom the ancient Greeks called the Pleiades. A V-shaped grouping of stars, the Hyades, stands between them and Orion. There are subtle differences, he says, in cultural interpretations of this guardian constellation. The Greek version has the Hyades appearing as Taurus the bull preventing Orion from reaching the girls. Meanwhile, some Australian Aboriginal traditions tend to depict Orion as a womanizer who falls in love with the sisters—but their older sibling stands in his way. 

In many of the versions of the story, the details of this pursuit and defense reflect the motion and dynamics of the stars themselves. Because of the Earth’s rotation, these constellations move across the sky throughout the night, with Orion appearing to chase the Pleiades. Some Aboriginal cultures see Orion as upside-down with the red of the star Betelgeuse in his right hand as fire magic that the warrior creates to battle the elder sister, Hamacher says. Meanwhile, the red star Aldebaran in her left foot (often seen as the red eye of the bull in Greek traditions) is about to kick sand in his face. The fire magic flickers and grows as they face-off, reflecting how Betelgeuse, which is a variable star, dims and brightens over 400 days. 

From legends to machines

The period of time when people created stories about shapes in the sky also matters. For example, Brown says, many of the Western culture’s constellations as seen from the Northern Hemisphere are more mystical creatures and tales, based on Greek mythology. Those constellations were described in an anthropology of constellation stories written in the third century BCE, so many were likely identified long before that. Thousands of years later, Western explorers into the Southern Hemisphere documented the patterns they saw in the stars on their travels to include more technical tools, particularly instruments for navigation, like a sextant or a compass. 

“You’ll find loads of things that are far more associated with the Age of Discovery,” Brown says. “That’s not surprising because our cultural group started to explore the Southern Hemisphere at a time when all of these clocks and things would have been far more prominent.”

[Related: Dark energy camera gives a tasty view of a lobster-shaped nebula]

But what those Western explorers didn’t consider, Brown says, was those groups of stars that had been identified and named thousands of years earlier in the Southern Hemisphere night sky by the people who were already living there—with very different interpretations.

“This is why I always stress that the Western, Greek constellations are just one way in which these patterns can be interpreted,” Brown notes. Listening to the ways people around the world make sense of the patterns they see in the stars can illuminate aspects of their culture and what is relevant to them.

Hamacher and his colleagues are conducting experiments to see what kinds of constellations people make up on their own. In a planetarium, they present audiences with a simulated night sky with stars in fake positions. When modern viewers connect the dots to make shapes, he says, it reflects their culture and geography. “You’re not going to get a lot of Australians who are going to see a squirrel in the stars, and Americans are not going to see a koala,” Hamacher says. 

Constellations without stars

Stars aren’t the only thing visible in the night sky, Hamacher adds: There are also nebulae planets and the moon. And in some parts of the world, the night sky gets dark enough to see the dark voids where starlight is absent in the Milky Way.

In the Southern Hemisphere, those spaces are often traced into what are called dark constellations. Because the air is much less humid in Australia than many other parts of the world, the continent is a particularly good place to see some of the darkest night skies.

Some cultures also see similar patterns in dark constellations, too. For example, Hamacher says, Aboriginal cultures see an emu in the dark space of the Milky Way between the Southern Cross and Sagittarius. In South America, some people also see a large flightless bird called a rhea.

Many stellar patterns only appear during certain times of the year (others, that linger near the poles, are visible all year long). In Australia, the emu starts becoming visible in the evening during the same time of year when the birds are breeding, building their nests, and laying their eggs. Because people would typically go out and forage those eggs, Hamacher says, the seasonal appearance of the dark emu constellation also served as a sort of harvest calendar for people. 

[Related on PopSci+: This Colorado community fought to save its darkness]

Light pollution can be another factor in how different people view the stars. Today, the artificial bulbs that illuminate the night also interfere with starlight, washing out the Milky Way and all but the brightest stars for millions of residents in urban, suburban, and adjacent areas.

“But they don’t fade away entirely. I just need to look into my Stellarium app,” Brown says, referencing one app to help users identify constellations. “We still have access and knowledge about what’s in the sky. We engage with the sky now in a completely different manner, in this kind of virtual way.”

Constellation apps also offer viewers access to night sky knowledge from across the globe. Users can see the various cultural interpretations of the patterns in the stars splayed across their screens as they peer at the night sky. 

“You can learn about so many other cultures because you can look into the sky. You’re straightaway in touch with something that somebody in the depths of the Amazon might see, and that somebody might have seen when they were building the pyramids,” Brown says. “That’s our shared heritage.”

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The moon’s soil is filled with small spheres of glass. These pieces of glass, often called beads, formed millions of years ago when asteroids slammed into the lunar surface, according to a new study published Wednesday in the journal Science Advances. 

But these microscopic lunar glasses–which range in size from a few tens of micrometers to a few millimeters–don’t just tell the moon’s story. They also offer a window into meteorite impacts on Earth, too. The research team found that the moon’s collisions occurred around the same time as many of Earth’s most notorious impacts—including the one that scientists say was responsible for wiping out the dinosaurs (except for birds).

“The moon is kind of our witness to what the history of large impacts really is in our neighborhood of the solar system,” says Rhonda Stroud, director of the Buseck Center for Meteorite Studies at Arizona State University who was not involved in the news study. Understanding the impact history of our corner of the solar system, Stroud adds, could help improve scientists’ models to anticipate the frequency of asteroids that hurtle toward us.

The tiny glass orbs at the center of this new research came directly from the moon. They were brought to Earth via China’s Chang’e-5 moon mission, which returned samples to scientists’ waiting hands and labs in December 2020. These fresh moon rocks were shared in research collaborations around the globe, and the international team behind the new Science Advances paper quickly began analyzing the spheres in the lunar samples.

[Related: The asteroid that created Earth’s largest crater may have been way bigger than we thought]

The team determined that these glasses formed anywhere from 2 billion to just a few million years ago, says Katarina Miljkovic, associate professor in the School of Earth and Planetary Sciences at Curtin University and an author on the new paper. 

When an impactor such as an asteroid slams into a world’s surface, she explains, the energy of that collision ejects material out. Some of the kinetic energy can heat up that matter while it’s in flight. Some of it melts, if it heats up enough. Because it is in flight when it melts and then cools again, Miljkovic says, that molten material hardens into a spherical shape, falling back to the ground as glass beads. 

The researchers analyzed the glass beads brought back by Chang’e-5 to determine their age, size, and other characteristics. They also looked at remote sensing data of craters on the moon to determine which impact events might have thrown out the specific lunar glasses that they studied. 

Though the team found a large span of ages for the beads and their associated craters, some periods were richer in beads. “There were actually peaks of ages, clusters of beads at a certain age,” Miljkovic says. 

Those peaks, Miljkovic says, likely identify significant events. Perhaps, she says, simply more asteroids traveled through the area and hit the moon at once, or maybe a big asteroid broke up nearby and sent a flurry of impacts raining down on the moon. 

The team also noticed the peaks’ timing often aligned with significant impact events on Earth. For example, Miljkovic says, one peak seems to coincide with the ages of a large collection of meteorites found on our planet. 

“The moon is our satellite, and relatively speaking, on an astronomical scheme of things, the Moon and Earth are close. They occupy almost exactly the same space in the solar system,” Miljkovic says. So if a group of space rocks were to come hurtling our way, it would make sense that both celestial bodies would be hit around the same time.

The challenge, however, is that Earth does not retain a clear record of impacts. That’s because, unlike the moon, our planet undergoes erosion, weathering, and planetary processes that bury craters, impact glasses, and other evidence, Stroud says. “Earth is also covered with oceans and trees and soil and cities,” they add. “A lot of craters are still hidden. It takes a long time to recognize them and some of their signatures are just gone.”

Meanwhile, on the moon, the evidence of impacts is littered across the surface in the form of craters and these glass beads. So the lunar surface is a helpful tool for researchers piecing together our own planet’s history.

One of the most famous impact sites on Earth is the Chixculub crater in the Yucatán Peninsula in Mexico. That 6-mile-wide crater is thought to be where an asteroid slammed into the Earth some 66 million years ago, triggering a mass extinction event that killed the non-avian dinosaurs. 

It turns out, one of the peaks in the lunar impact data in the new study corresponds to that timing. “We’re just showing that the ages are coinciding,” Miljkovic says. But it’s possible that there might have been companion asteroids flying along with the dinosaur-killing space rock when it encountered the Earth-Moon system and some of them hit the lunar surface, too.

What happened on the moon at that time isn’t the only evidence that there were multiple asteroids causing collisions in our neighborhood around 66 million years ago. In August in a different paper in Science Advances, another research team described what might be another impact crater on Earth formed at the same time offshore of West Africa. If it’s confirmed, this crater could support the idea that a large asteroid broke into pieces and those fragments crashed into both Earth and the moon at the end of the Cretaceous period.

[Related: A second asteroid may have crashed into Earth as the dinosaurs died]

Tying craters on the moon to impact sites on Earth is tricky business, Stroud cautions. “It’s interesting and promising,” they say, but “the links to the craters on Earth are still speculative.” The “smoking gun,” Stroud says, would be to be able to match the composition and age of impacting material from both worlds. But, though the study authors can’t directly connect any moon craters to ones here, this research “shows the power of well-planned sample return” that provides the geologic context of the samples. 

“Maybe we’re onto something,” Miljkovic says. “We can only look at evidence and estimate the likelihood of something happening, but that’s the kind of story that, if true, is really cool.”

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When the first stars and galaxies formed, they didn’t just illuminate the cosmos. These bright structures also fundamentally changed the chemistry of the universe. 

During that time, the hydrogen gas that makes up most of the material in the space between galaxies today became electrically charged. That epoch of reionization, as it’s called, was “one of the last major changes in the universe,” says Brant Robertson, who leads the Computational Astrophysics Research Group at the University of California, Santa Cruz. It was the dawn of the universe as we know it.

But scientists haven’t been able to observe in detail what occurred during the epoch of reionization—until now. NASA’s newly active James Webb Space Telescope offers eyes that can pierce the veil on this formative time. Astrophysicists like Robertson are already poring over JWST data looking for answers to fundamental questions about that electric cosmic dawn, and what it can tell us about the dynamics that shape the universe today.

What happened after the big bang?

The epoch of reionization wasn’t the first time that the universe was filled with electricity. Right after the big bang, the cosmos were dark and hot; there were no stars, galaxies, and planets. Instead, electrons and protons roamed free, as it was too steamy for them to pair up. 

But as the universe cooled down, the protons began to capture the electrons to form the first atoms—hydrogen, specifically—in a period called “recombination,” explains Anne Hutter, a postdoctoral researcher at the Cosmic Dawn Center, a research collaboration between the University of Copenhagen and the National Space Institute at the Technical University of Denmark. That process neutralized the charged material.

Any material held in the universe was spread out relatively evenly at that time, and there was very little structure. But there were small fluctuations in density, and over millions of years, the changes drew early atoms together to eventually form stars. The gravity of early stars drew more gases, particles, and other components to coalesce into more stars and then galaxies. 

[Related: How old is the universe? Our answer keeps getting better.]

Once the beginnings of galaxies lit up, the cosmic dark age, as astrophysicists call it, was over. These stellar bodies were especially bright, Robertson says: They were more massive than our sun and burned hot, shining in the ultraviolet spectrum. 

“Ultraviolet light, if it’s energetic enough, can actually ionize hydrogen,” Robertson says. All it takes is a single, especially energetic particle of light, called a photon, to strip away the electron on a hydrogen atom and leave it with a positive electrical charge. 

As the galaxies started coming together, they would first ionize the regions around them, leaving bubbles of charged hydrogen gas across the universe. As the light-emitting clusters grew, more stars formed to make them even brighter and full of photons. Additional new galaxies began to develop, too. As they became luminous, the ionized bubbles began to overlap. That allowed a photon from one galaxy to “travel a much larger distance because it didn’t run into a hydrogen atom as it crossed through this network,” Robertson explains.

At that point, the rest of the intergalactic medium in the universe—even in regions far from galaxies—quickly becomes ionized. That’s when the epoch of reionization ended and the universe as we know it began.

“This was the last time whole properties of the universe were changed,” Robertson says. “It also was the first time that galaxies actually had an impact beyond their local region.”

The James Webb Space Telescope’s hunt for ionized clues

With all of the hydrogen between galaxies charged the universe entered a new phase of formation. This ionization had a ripple effect on galaxy formation: Any star-studded structures that formed after the cosmic dawn were likely affected. 

“If you ionize a gas, you also heat it up,” explains Hutter. Remember, high temperatures it difficult for material to coalesce and form new stars and planets—and can even destroy gases that are already present. As a result, small galaxies forming in an ionized region might have trouble gaining enough gas to make more stars. “That really has an impact on how many stars the galaxies are forming,” Hutter says. “It affects their entire history.”

Although scientists have a sense of the broad strokes of the story of reionization, some big questions remain. For instance, while they know roughly that the epoch ended about a billion years after the big bang, they’re not quite sure when reionization—and therefore the first galaxy formation—began. 

That’s where JWST comes in. The new space telescope is designed to be able to search out the oldest bits of the universe that are invisible to human eyes, and gather data on the first glimmers of starlight that ionized the intergalactic medium. Astronomers largely detect celestial objects by the radiation they emit. The ones farther away from us tend to appear in the infrared, as the distance distorts their wavelengths to be longer. With the universe expanding, the light can take billions of years to reach JWST’s detectors. 

[Related: Astronomers are already using James Webb Space Telescope data to hunt down cryptic galaxies]

That, in a nutshell, is how scientists are using JWST to peer at the first galaxies in the process of ionizing the universe. While older tools like the Hubble Space Telescope could spot the occasional early galaxy, the new space observatory can gather finer details to place the groups of stars in time.

“Now, we can very precisely work out how many galaxies were around, you know, 900 million years after the big bang, 800, 700, 600, all the way back to 300 million years after the big bang,” Robertson says. Using that information, astrophysicists can calculate how many ionizing photons were around at each age, and how the particles might have affected their surroundings.

Painting a picture of the cosmic dawn isn’t just about understanding the large-scale structure in the universe: It also explains when the elements that made us, like carbon and oxygen, became available as they formed inside the first stars. “[The question] really is,” Hutter says, “where do we come from?” 

Correction (September 21, 2022): The fluctuations in the early universe’s density took place over millions of years, not billions as previously written. This was an editing error.

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Today, our solar system is fairly stable. There are eight planets (sorry, Pluto) that keep constant orbit around the sun, with little risk of being crushed by asteroids. But it wasn’t always that way.

Some 4.5 billion years ago, as the solar system was just forming, large chunks of rocks frequently collided with slow-growing dwarf planets. The results were often cataclysmic for both bodies, reducing them to debris that still pummels Earth today. But sometimes those violent collisions yielded the creation of something shiny and new—perhaps even diamonds.

That’s likely what happened when an asteroid smashed a dwarf planet into smithereens in those earliest days of the solar system, according to a new paper published this week in the journal Proceedings of the National Academy of Sciences. The collision was so violent, the authors say, that it triggered a chain of events that transformed graphite from the dwarf planet’s mantle into diamonds now found in meteorites.

The explosive process through which these space gems formed, the researchers say, might even inspire a method to make lab-grown diamonds that are tougher than the ones people mine.

“We always say a diamond is the hardest material. It’s natural, nothing we’ve been able to make in the lab is harder than diamond. Yet, there have been hints of research over the years that there are forms of diamond that appear to actually be harder than single-crystal diamonds. And that would be immensely useful,” says Laurence Garvie, a research scientist in the Center for Meteorite Studies at Arizona State University, who was not involved in the new research. “Here’s a hypothesis that may add a new understanding of how these materials are formed.” And such a possibility, he adds, is tantalizing for all kinds of industrial and consumer uses.  

[Related: Meteorites older than the solar system contain key ingredients for life]

On Earth, diamonds emerge when carbon deposits are subjected to high pressure and high temperatures, typically from the geo processes rumbling deep under the planet’s crust. But that explanation never made sense for a carbon-rich meteorite, called a ureilite, that’s mysteriously filled with space diamonds. It takes a fair amount of mass to exert enough pressure on the carbon, Garvie explains, much more than the dwarf planet that these ancient rocks probably came from. Instead, some meteoriticists have proposed that shock from an impact triggered the transformation. 

But shock alone doesn’t completely explain the crystals in the ureilites, says Alan Salek, a physics researcher at the Royal Melbourne Institute of Technology and one of the authors on the new paper. For example, the meteorites’ diamonds are much larger than any created in laboratory experiments that mimicked the proposed conditions, he says. 

Furthermore, scientists have found inconsistencies in the urelites’ composition. Some don’t appear to have any hints of diamonds. Others contain carbon crystals that look notably different from engagement ring stones: The structures have more folds, with atoms that appear to be hexagonal rather than cubic. Those extra sides are thought to make the material harder.

But as Andrew Tomkins, a geoscientist at Monash University who led the latest research, writes in an email to Popular Science, “of course everyone knows that diamond is very hard, so it should be impossible to fold.” 

After studying the atomic properties of the carbon in ureilites, Tomkins, Salek, and their colleagues devised a scenario they say can explain all of the gems’ quirks. The story goes that when an asteroid slammed into a dwarf planet in the active early solar system, it barreled deep into the ureilite parent body and triggered a sequence of events. 

The dwarf planet contained folded graphite in the dwarf planet. Once the asteroid hit, the violent collision released pressure from the mantle, much like when you twist the lid off a soda bottle, Tomkins explains. This rapid decompression caused a bit of the mantle to melt and release fluids and gases, which then reacted with minerals. The activity forced the folded graphite in the planet to transform into the hexagonal crystals. Later, as the pressure and temperature dropped, regular cubic diamonds formed, too. 

The hexagonal structure of the crystals are still the subject of some controversy. Some scientists argue that the shape makes them a different kind of diamond known as lonsdaleite. The gem was first identified in Crater Diablo in Arizona in 1967, and has since been found at other impact sites around the world. Others have suggested that the material is something like a snapshot of disordered diamond formation. Garvie and his colleagues have given alternate explanations, such as diamonds with graphine-like intergrowths. But Salek and Tomkins say their new research definitively proves that the ureilite-based gems are indeed hexagonal diamonds, and therefore, should be classified as lonsdaleite.

[Related: Earth has more than 10,000 kinds of minerals]

However it’s defined, scientists tend to agree that this substance could have valuable properties. One attempt to recreate lonsdaleite indirectly measured the material to be 58 percent stronger than its cubic counterpart.  If the substance can be made artificially in a laboratory, Garvie says “the possibilities are endless,” describing potential uses for protective coatings on, say, an iPhone or a camera lens. Salek suggests creating saws and other cutting implements with blades so hard that they can’t get dull. 

The crystals Salek and Tomkins found, however, are just about 2 percent of the size of a human hair. So don’t expect to profess your love with a rare ureilite diamond anytime soon. But, Salek adds, “the hope is to mimic the process [from space] and make bigger ones.”

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Astronomers typically divide the planets in our solar system into two types: Rocky worlds and gas giants. But, according to a new study of planets in other star systems in our galaxy, there’s a third kind of world, which is made up of about 50 percent water and 50 percent rock. And such a water-rich world is a tantalizing place for astronomers to test their hypotheses about what makes a planet capable of supporting life. 

“Within our lifetimes, we may, for the first time, be able to say something scientifically proven about habitability on other planets,” says Rafael Luque, a postdoctoral fellow at the University of Chicago who is the first author on the new study published Thursday in the journal Science. “And that’s a major, major step.”

In recent years, astronomers have been rapidly detecting new planets orbiting stars beyond our own, called exoplanets. To date, more than 5,000 exoplanets have been discovered and confirmed. But figuring out exactly what those worlds look like—and therefore whether or not they might be habitable—from light years away is a difficult feat. 

Most exoplanets have been discovered using what is called the transit method, which identifies a planet indirectly by observing how its star’s light dims slightly when the planet passes in front of it. Astronomers can also infer the radius of an exoplanet by how much starlight it blocks. Scientists have used that information to compare these alien worlds with the planets in our own solar system as a way of hypothesizing what they might look like. A planet with the same radius as Earth, for example, is thought to be quite rocky.

But in orbit around many red dwarf stars, which are by far the most common stars in our galaxy, there’s a kind of planet that doesn’t have an analog in our solar system. Based on their radii, these worlds fit in the gap in size between Earth and Neptune. 

[Related: Newly discovered exoplanet may be a ‘Super Earth’ covered in water]

The thinking among astronomers has long been that those small planets fit into two categories: some were thought to be “super-Earths” and some were “mini-Neptunes.” This idea was bolstered by the observation of a dearth of exoplanets that had a radius around 1.6 times that of Earth, which is called a “radius valley,” explains Ravi Kopparapu, a planetary scientist at NASA’s Goddard Space Flight Center who was not involved in the new study. The way that a star’s radiation erodes a planet’s atmosphere, he says, has been thought to explain that gap in radii.  

By that logic, “super Earths,” which were on the smaller side of that radius valley, were left with very thin atmospheres and a largely exposed rocky surface. “Mini-Neptunes,” on the other hand, had retained thick, puffy atmospheres and therefore these gassy planets had larger radii. 

But there could be other ways to build an exoplanet to have those radii. Because they have no analogues in our solar system, these worlds could be truly alien. So to figure out what materials might make up these distant planets, Luque and his collaborator Enric Pallé sought to determine their density.

Density isn’t something that can be measured directly from so far away, but with a planet’s mass and radius, it’s a simple calculation (mass divided by volume equals density). The researchers used the radius and mass measurements from 34 planets newly detected by the Transiting Exoplanet Survey Satellite (TESS), which launched in 2018, to gather a sample of densities for these mysterious small exoplanets.

[Related: We may be underestimating how many cold, giant planets are habitable]

Based on their calculations, the radius valley is not what separates the different types of planets in orbit around red dwarf stars. It’s density. And they extrapolated that those exoplanets can be one of three types of world: rocky, gaseous, or, the new type, water-rich. 

“We may think of Earth as a water-rich planet, but the water on Earth is just 0.02 percent of its total weight,” Luque says. The density of these distant water worlds, meanwhile, indicates that about half of their mass is water. 

But don’t start picturing a world with a rocky core and a deep ocean of water sloshing around on top of it, exposed to space, Luque says. “What we’ve seen in our sample is that this water cannot be on the surface,” he says. “The water may be trapped below the surface or maybe mixed with the magma, but it is not going to be in the form of deep, deep oceans–at least not at the surface.”

The closest analogues that we have in our own solar system to such water-rich worlds are the moons of Jupiter and Saturn. For example, Europa, one of Jupiter’s moons, has a deep ocean sloshing around under a global water ice shell. 

It’s unlikely that these exoplanets have a water ice shell, Luque says, because they are much closer to their star–any water on the surface would evaporate. That is, at least, on the sun-facing side of the planet. These worlds do not turn on their axis to have a day and night cycle like Earth does. Instead, there is a permanent light and dark side. However, Luque says, perhaps there is a region where the light and dark side meet, in a sort of a perpetual twilight, where the temperature on the surface might be just right for liquid water to be stable. 

In the search for habitable worlds, astronomers typically use liquid water as a guide. That’s because it is essential for life as we know it (that is, life on Earth, because it is the only life we know of so far). 

“We only have one template of life in this universe, so we use that as a template to find life elsewhere,” Kopparapu says. But stable liquid water isn’t the only thing needed to make a place habitable by that definition, and just because a place is capable of supporting life doesn’t mean that something lives there, he adds. 

To investigate the habitability of these distant worlds, astronomers will turn to tools like the newly-launched James Webb Space Telescope (JWST), which can peer into the chemistry of exoplanet atmospheres to reveal more details about their composition. With telescopes like JWST, astronomers will look for water vapor to confirm the presence of H2O as well as gases like methane, oxygen, carbon dioxide, nitrogen, and more that are found in Earth’s atmosphere. 

“We are finding more and more evidence that there are a lot of potentially habitable worlds. Our Earth is not unique,” Kopparapu says. He uses an analogy: “If you move into a new neighborhood, and you want to introduce yourself to your neighbors, you may see a lot of houses but you don’t see many people. So we are finding lots of houses. Now we just need to find people.”

The post A new class of super-watery planets may exist beyond the solar system appeared first on Popular Science.

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A trip to Mars will be difficult, to say the least. Although human spaceflight has become a regular occurrence in near-Earth space in recent decades, leaving our gravitational pull takes a lot of rocket power. And then leaving a planet like Mars to return to Earth will also take a lot of oomph. 

But NASA, other spaceflight agencies, and private companies have set their sights on putting humans on Mars—and returning them to Earth safely. So engineers and scientists are working to figure out how to make enough propellant to make such a trip possible. 

Oxygen, an essential component of rocket propulsion, is hard to come by on the Red Planet. But results from a prototype machine on Mars suggest the element can be yanked out of the air—hinting at future productions to power rocket launches, but not yet nearly enough for humans to breathe Martian air directly.

“It’s really difficult, if not impossible, to design a human Mars mission that doesn’t use in situ resources,” says Carol Stoker, a planetary scientist at NASA Ames Research Center who was not involved in the project, using the scientific term for “on site.”

Now, a lunch-box-sized device piggybacking on the Perseverance rover has opened the door to producing propellant from resources found on Mars. The Mars Oxygen In Situ Resource Utilization Experiment (MOXIE), has successfully produced oxygen on the Red Planet.

From the time that Perseverance landed in February 2021 to the end of that year, MOXIE produced about 50 grams of oxygen over seven runs, according to a report published Wednesday in the journal Science Advances. MOXIE has continued to run experiments under various conditions into 2022, says MOXIE deputy principal investigator Jeffrey Hoffman, a professor of aeronautics and astronautics at the Massachusetts Institute of Technology. 

The device can produce 6 to 10 grams per hour, depending on atmospheric conditions. It set that production maximum rate at the end of August, Hoffman says, when the Martian atmosphere was densest.

The purpose of MOXIE, Hoffman says, “is to verify that the process actually works on Mars. And that, I would say, we are well on the road to doing.”

[Related: 5 new insights about Mars from Perseverance’s rocky roving]

MOXIE uses the molecules that make up Mars’s atmosphere to create oxygen. But it’s not a simple extraction. The Martian atmosphere is 95 percent carbon dioxide (Earth’s atmosphere is mostly nitrogen with a large portion of oxygen as well). MOXIE has to split the CO2 molecules into carbon monoxide and oxygen. 

First, MOXIE draws in air through a HEPA filter, which keeps Martian dust out of the process. Then the Martian air goes through a compressor because, as Hoffman explains, it is not dense enough for the oxygen-producing process. The device compresses the Martian air, significantly increasing its density: from 100 times thinner than Earth’s atmosphere to about half as thin. 

Then, the carbon dioxide is heated up to about 1,500° F (800°C). Once heated, it’s time for the main event: A run through the electrolysis unit, which uses electricity to drive a chemical reaction. In there, the carbon dioxide encounters catalysts, like nickel, which cause the CO2 molecule to dissociate into carbon monoxide (CO) and an oxygen ion. Then electricity is used to pull oxygen ions through a filter into another chamber, where they combine into oxygen molecules. The result is pure oxygen that can be used for breathing or for rockets. 

“The nice thing about MOXIE is that, from the oxygen side of it, all you need is the atmosphere,” Hoffman says. “So it doesn’t matter where you are, you can go anywhere you want, and you’ve got atmosphere.”

[Related: This miniature rocket could be the first NASA craft launched from Mars]

MOXIE has produced oxygen throughout Mars’s nights, during the day, and in multiple seasons–even the winter. During the coldest months on Mars’s poles, the atmosphere’s density reduces because carbon dioxide deposits onto the polar surface as ice. That means there’s less CO2 available for MOXIE every six months, explains Margaret Landis, a research scientist in the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder. Still, it produced about 6 grams per hour during those times that the atmosphere thinned. 

“MOXIE can run any time on Mars,” Hoffman says. “If we get some more runs, we’re going to try running it at dawn and dusk when the conditions are changing rapidly, and we can show that MOXIE can adapt to those changing conditions.”

A rate of 6 to 10 grams an hour, however, will not produce nearly enough oxygen to be useful for a human mission to Mars. The average human breathes a little less than 1 kilogram of oxygen each day, Hoffman says, and rockets are even hungrier for O2. It will take tens or even hundreds of tons of oxygen to power a rocket that can launch people off the surface of Mars. But that oxygen can be accumulated over time. A full-scale version of a MOXIE-like system would need to produce something like 2 to 3 kilograms an hour of oxygen, Hoffman says, to have any chance of amassing enough liquid oxygen to use in the rocket launch system. 

Engineers already have a prototype of such a larger device, he says. Because MOXIE had to hitchhike on the Perseverance rover, it was kept small, but a future mission could send a larger MOXIE-like device to Mars on its own. Hoffman says that such a device might also have more features, like perhaps the ability to make the carbon monoxide product into something useful as well.

The ability to produce oxygen doesn’t mean that Mars-launching rockets are ready to go. Oxygen is only one part of the rocket-launch equation, says NASA’s Stoker. It provides half of a combustion reaction–the oxidizer–but a rocket still needs other ingredients for fuel. But, she adds, oxygen could supply more than three-quarters of the mass needed to propel a rocket, and that greatly reduces the amount of stuff that has to be carried to the Red Planet from Earth.

As a MOXIE-like technology is scaled up, Landis says, it’s worth considering the environmental impact that this process might have on Mars. “It’s something to think about because CO2 is a major component of Mars’s atmosphere, and plays a really major role in its seasonal cycle,” she says. “There’s still a lot to learn about the exact implications of what’s going to happen if you start changing this equilibrium between surface and atmospheric CO2” and the types of gases. 

“It sometimes does feel like you’re living in a science fiction future,” Landis says. “This is a testament to how much we’ve been able to do on Mars.”

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When NASA’s Saturn V rocket launched humans to the moon a half-century ago, each blast-off amazed onlookers with its power. Flames from the launch dazzled. Its explosive liftoff was thunderously loud. It captured the imaginations of many around the world, and still holds a place in spaceflight lore.

Some tales of Saturn V’s power dramatize the acoustic potency of that explosive moment. Allegedly, the sound of the launch melted concrete and set nearby grass on fire. 

Aeroacousticians have new calculations that confirm that any such effects were certainly not caused by the sound of the launch, described in a new paper published August 23 in The Journal of the Acoustical Society of America. But, they say, the roars of really big rockets like the Saturn V are increasingly important to understand. NASA’s latest rocket—its biggest ever, the Space Launch System (SLS)—will launch the Artemis I mission as early as Monday. Meanwhile, government and commercial spaceflight endeavors are rapidly expanding around the globe. 

“If you’ve been to a launch, the acoustics are enormous,” says Kent Gee, a professor of physics at Brigham Young University and lead author on the new paper. But understanding the intensity of the sound isn’t just about what you might hear nearby a rocket launch. “If you don’t understand the acoustics produced by the rocket, you can’t design payloads efficiently,” he says, because rocket launch acoustics can cause damage to everything onboard. And that could make spaceflight unnecessarily challenging as humanity pushes deeper into the cosmos.

[Related: What we learn from noisy signals from deep space]

Rocket launch noise comes from a complex combination of sources, says Caroline Lubert, a professor of mathematics and an aeroacoustician at James Madison University, who was not an author on this new paper but has collaborated previously with Gee to reassess the last half century of rocket noise, a body of work that underpinned the new Saturn V paper. Aeroacousticians are most concerned about the vibrations caused by rocket noise, which can damage the craft, its payloads, or even launchpad structures. Those structures can also magnify rocket acoustics by reflecting sounds. 

And with spaceports cropping up in new places across the globe, Lubert says, noise pollution from launches is a growing concern for surrounding communities and wildlife.

New calculations to predict how noisy a launch will be are in order. Many of the ideas about the acoustical power of rocket launches is based on noise research that was done leading up to NASA’s Apollo program in the 1960, Gee says. And some of that older information was based on observations rather than directly recorded data. Determining the actual impact of the Saturn V launch allows engineers to draw direct comparisons between that lunar launch and the upcoming ones. 

When Gee and colleagues were investigating the historical records of rocket launch acoustics, he found that the reports about Saturn V’s launch sound levels varied dramatically. Some reports suggested that the sound levels of a Saturn V launch were as low as 180 decibels, while others reported as high as 235 decibels. (For context, commercial jet engines range from about 120 to 160 decibels.) And, because that is a logarithmic measure, every 10 decibels is an order of magnitude increase.

“Putting that in the perspective of a lightbulb, that’s like saying that a 10-watt lightbulb and a mega-watt lightbulb are the same thing,” Gee says. “People really didn’t have a good understanding of what the levels were and what they were saying about those levels.”

Part of the challenge when evaluating sound, Gee explains, is that there are two different things measured in decibels: sound power and sound pressure. Sound power, he says, refers to the total amount of sound energy produced by the rocket. Sound pressure, on the other hand, is the amount of sound that reaches a given distance. The farther away from the source of a noise, the quieter it is and therefore the less sound pressure at that point. 

It’s likely that some of the reports of lower decibels emitted from a Saturn V launch come from measures of sound pressure rather than sound power, he says. 

[Related: NASA recorded a black hole’s song, and you can listen to it]

When Gee and his team made a computer model of the sound power of a Saturn V launch based on the rocket’s thrust and other characteristics, they found that it would have produced about 203 decibels of sound power. That’s really, really loud—but not loud enough to melt concrete or start a grass fire. “Mankind has not produced a sound source that would be capable of that, purely from the sound waves,” Gee says. For a comparison, he says, the acoustics of a Saturn V launch would be the same amount of sound as about 700 military aircraft flying simultaneously.

Gee and his team expect the SLS launch of Artemis I to produce a similar amount of sound power to the Saturn V, perhaps one decibel higher. “There’s a little bit more thrust and a little bit more power produced by the rocket as it launches, we would use that and the modeling that we’ve done previously,” he says, “we would take that same approach and that would suggest that the SLS will be a little bit louder than the Saturn V.”

But it’s also possible that SLS ends up being more muffled due to NASA’s modern noise-suppression system, Lubert says. “We’ve done other things to compensate [in the half a decade since the Saturn V launched],” she says. “There’s so much variability and a lot of uncertainty in predicting vibroacoustic load.”

On Monday, when the SLS is slated to launch Artemis I, Gee and his team will be nearby. They’ve set up sensors at strategic points selected based on their Saturn V research, ready to check whether NASA’s most powerful rocket yet will also be its noisiest.

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When NASA’s Artemis 1 mission launches to the moon later this month, on board the Orion space capsule will be two special passengers: Helga and Zohar. 

The pair are actually mannequin torsos, called phantoms, that are inspired by hospital training tools and are made to mimic human bones, soft tissues, and the internal organs of an adult female. They were borned out of a collaboration with the Israel Space Agency and the German Aerospace Center, and are designed with sensors that can map radiation exposure levels throughout the body. Zohar, specifically, will wear a radiation protection vest designed to protect the real astronauts slated for future Artemis missions—including the first women to go to the moon.

The last time people set foot on the moon or even traveled beyond low Earth orbit was at the end of the Apollo program in 1972. Back then, the US astronaut corps did not admit women. That changed when the first American female astronaut candidates were selected in 1978, with a young Sally Ride among them.

Today, NASA astronauts are much more diverse. But that isn’t reflected in the data informing their safety protocols because of decades of male dominance in the field. So, the agency and its collaborators are firing up new experiments to understand how different human bodies respond to the extreme environment of space—and best enable all astronauts to do their jobs safely.

[Related: A brief history of menstruating in space]

“We stand on the shoulders of giants, and we’ve made a lot of progress. But there’s a lot of progress still to be made to understand [the biological nuances between astronauts],” says Jennifer Fogarty, chief scientific officer for the Translational Research Institute for Space Health, which is supported by the NASA Human Research Program and led by the Baylor College of Medicine. The goal, she says, is to build spaceflight tools and healthcare regimens for astronauts “around the human body to give it the ability to do the job you’re expected to do, and reduce the possibility of getting into conflict with that body.”

Wear and tear in zero-g

To look for patterns, researchers like Fogarty have been collecting data on how sex differences might influence astronauts’ health in space. So far, however, the research on how female bodies respond to the extreme environment of space has been “pretty limited,” she says. To date, more than 600 people have flown in space; fewer than 100 of them have been women. Tools like Helga and Zohar can help gather data in a way that isn’t reliant on historic trends.

Scientifically, it’s difficult to extrapolate trends in sex differences or sex-specific healthcare that can be trusted based on those numbers because some characteristics could simply be from individual variation. For example, when a female astronaut developed a blood clot while on the International Space Station in 2020, it prompted an investigation into whether the use of hormonal contraceptives for menstrual cycle control increased the risk of clotting during spaceflights. A review of 38 female astronaut flights published later that year concluded that it does not. But given such a small sample size and how rare blood clots associated with hormonal contraceptives are, that question remains open.

In some ways, women have proven particularly “resilient” during spaceflight, Fogarty says. For example, male astronauts’ eyesight seems to be more affected by swelling around the optic nerve in zero gravity than female astronauts’. But according to a 2014 study, female astronauts have statistically experienced greater orthostatic intolerance (the inability to stand without fainting for a long period of time) upon returning to Earth.

Radiation poisoning from space

Beyond short-term conditions and changes to bodies, a lot of the focus on human health out in space is focused on exposure to cosmic radiation from stars and galactic explosions. Most of the data we currently have comes from laboratory research on rodents or observations on atomic bomb survivors, Fogarty says: It shows a pattern of female survivors being more susceptible to developing lung cancer than male ones. 

Because women seem to carry more side effects from radiation damage than men, NASA recently updated its standards for acceptable levels of exposure to be uniform, limiting all astronauts to what was previously the allowable dosage for a 35-year-old woman.

Galactic cosmic rays are different from nuclear weapon radiation, however. For one, in nuclear accidents or acts of war exposure is two-dimensional, which means certain organs might be hit with more radiation than others. But, in space, the radiation is “considered omnipresent,” Fogarty says—you’re exposed in every direction. Some calculations suggest that the radiation exposure rate on the moon is about 2.6 times higher than that experienced by astronauts aboard the International Space Station (ISS). Even then, in one week on the ISS, astronauts can be exposed to the same amount of radiation as humans are over one year on the ground.

With radiation coming from all angles in space, devising a physical barrier like a spacesuit or protective vest can be tricky. It makes understanding how all human organs are affected by radiation exposure important—whether they be sex-specific reproductive organs or not. 

That’s where Helga and Zohar come in. The female “phantoms” are part of the Matroshka AstroRad Radiation Experiment (MARE). Internally, they have a grid of 10,000 passive sensors and 34 active radiation detectors that will gather data for researchers on which parts of the body make the most contact with electromagnetic waves during spaceflight. Some organs may be protected by the layers of soft tissue over them, while others may not be—this will help engineers build more targeted systems to protect the most at-risk areas of the body from harmful radiation. 

“What we will get besides the difference between a man and a woman when it comes to biological effects, we will get the difference between different body organs. The difference between brain and uterus, for example,” said Ramona Gaza, MARE science team lead at NASA’s Johnson Space Center, in a press teleconference this week.

The two torsos won’t be the only Artemis 1 experiment designed to study the effects of radiation. There will also be a suite of live organisms, including yeast, fungi, algae, and plant seeds, aboard the mission. In a NASA project called BioSentinel, the Orion capsule will release a CubeSat into orbit around the moon carrying yeast cells to test on how the organisms survive the deep-space environment.

[Related: Long spaceflights could be bad for our eyes]

In total, the Artemis 1 mission will launch 10 CubeSats: The rest will study aspects of the lunar environment that will prove important to characterize for the safety of future human travel to the moon. They include tools to study space weather and bursts of solar radiation, map stores of water ice on the lunar surface, as well as a tiny lander from the Japan Aerospace Exploration Agency.

Helga and Zohar also won’t be the only “passengers” on Artemis 1. In addition to a stuffed a sheep, they will be joined by a male-bodied mannequin equipped with sensors to measure various aspects of the environment around the moon during the flight, including radiation exposure. While Helga and Zohar won’t be wearing spacesuits, Commander Moonikin Campos will be dressed in a first-generation Orion Crew Survival System, which Artemis astronauts will use when real humans return to the moon.

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Hal Levison was planning to take a nap when he got the bad news. 

NASA’s Lucy spacecraft rocketed off our planet at 5:34 a.m. on October 16, 2021, so Levison and his team had been up all night preparing. It was a spectacular, “picture perfect” launch, recalls Levison, who is the Lucy mission principal investigator from the Southwest Research Institute in Boulder, Colorado. The spacecraft would soon be on its way to the Trojan asteroids, unexplored fossils of the solar system that sit roughly the same distance from the sun as Jupiter. Those small space rocks, which are thought to have formed from the same processes that created the planets, could shed light on how our world came to be.

But then, just a few hours after launch, the team received data from Lucy that revealed that one of her two solar arrays–which power the spacecraft’s systems–hadn’t fully opened. Without both solar arrays deployed, the team wasn’t sure Lucy would make it to her intended destination.

“The basic mission was in jeopardy,” Levison says. There would be no time for a nap. “It was a very hard day.”

The team jumped into action to figure out what went wrong and to devise a solution. After months of sleuthing through the data, testing ideas on computer models and spare parts on the ground, and considering alternative trajectories for the scientific mission, the Lucy engineering team came up with a plan, which they set into action earlier this summer. Now, the spacecraft’s troublesome solar array is almost completely unfurled–enough so that the mission can continue as planned. 

“The state of the spacecraft is much, much healthier,” Levison says, calling the feat pulled off by the team’s engineers “totally amazing and brilliant.”

When the mission engineers first discovered the problem, they didn’t immediately know what had gone wrong. All the data showed them was that one of the solar arrays hadn’t completely unfurled and latched into place. The engineers couldn’t get a visual because Lucy’s cameras point outward. Everything came through data about the spacecraft’s performance.

Lucy’s solar arrays are like large folding fans. When the spacecraft launched, the arrays were folded up. To deploy them, a motor pulled on a lanyard attached to each array. Then, if it had reached full deployment, a latch would have held the edge of the array in place, keeping it from moving.

“What we think happened is somewhere along in the deployment, that lanyard got misaligned and came out of the spool that brings the lanyard toward the latching mechanism,” explains Mark Effertz, spacecraft lead engineer for Lucy at Lockheed Martin, which built the spacecraft. The team had no direct data about the lanyard being tangled, he adds, but they extrapolated that it “started to snarl on either side of the spool and create a kind of bundle of lanyard as the motor kept pulling.”

[Related: Is NASA launching too many asteroid missions?]

With the power supply in jeopardy, the engineers determined that they had two main choices, Effertz says: They could fly Lucy as-is, and change the course of the mission. Or, they could keep tugging on the lanyard. 

If the team decided to keep the solar array partly furled, Levison says, the science team would have likely had to select a new, less power-hungry trajectory for the spacecraft. And that would mean not going to the group of eight, hand-selected Trojan asteroids. 

Instead, he says, the spacecraft would travel a shorter distance to three small Trojans. Levison doesn’t mince words about that alternative plan, saying those asteroids are “much less interesting, scientifically.”

That’s because the original trajectory took Lucy by a richly diverse group of asteroids. They range in size and in color from gray to red, and are close together, making it possible for the spacecraft to study many in one trip. It’s their diversity that piqued Levison and others’ interests, because it likely means that these asteroids formed in far-flung areas of the solar system. Some probably hail from the outer solar system.

Levison likes to call the Trojan asteroids “fossils,” and even named the mission “Lucy” after the famous hominin fossil that has contributed significant insights to our current understanding of early human ancestors. This mission, he explains, aims to answer questions about our origins in other ways.

“Planets don’t form, if you’ll excuse the pun, in a vacuum,” Levison says. “Planetary systems form as part of an ecosystem where the growing planets are competing for food, they’re knocking each other around gravitationally, they move around.” The Trojan asteroids are remnants of the early parts of that evolutionary process and therefore windows into our planetary origins.

[Related: A rare gas is leaking from Earth’s core. Could it be a clue to the planet’s creation?]

So the team decided the original trajectory for the Lucy space mission was worth rescuing and devised a plan to yank the lanyard a bit harder in an attempt to fully deploy the snagged solar array. The spacecraft had a backup motor built into its system in case the primary motor to pull the lanyard failed. 

“We never really designed both motors to run at the same time. But we found that there was a way to” tell the spacecraft to do it anyway, Effertz says. Using both motors at the same time gives it more torque, or pulling power, he explains. Although this maneuver doesn’t detangle the snarled lanyard, it can wind up more of the lanyard onto the spool over the tangle, pulling the array open and holding tension on the line.

The team estimates that Lucy’s troubled solar array is now nearly fully open, though it isn’t secured in place with the latch. That configuration seems to be generating enough power to get Lucy to its original target Trojans.

The engineers are still considering pulling further on the lanyard in the hopes of getting it to latch. But there are risks associated, Effertz says. The tangle would get bigger and bigger, which could rub against the spacecraft and that might cause new problems. They have time to decide, however, as Lucy is currently flying through a region where the team can’t use the craft’s antenna to download the necessary data, Effertz says. So any further tweaks will have to wait until around November.

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NASA’s Perseverance rover is currently collecting rock and soil samples in Mars’s Jezero Crater that will one day be returned to Earth. Under the current plan, in 2030 the rover itself will deliver the sample tubes to a Mars lander for transport back home. But, if something goes wrong, a pair of small helicopters will be poised to swoop in, as NASA’s Mars Sample Return team announced in late July.

If that occurs, the Sample Recovery Helicopters will be the second and third rotorcraft ever to take flight on another planet. And their inclusion in the Mars Sample Return mission, a joint effort by NASA and the European Space Agency, could signal the beginning of a new chapter in Mars exploration—one in which small, lightweight helicopters regularly zip around the Red Planet. 

The news of adding helicopters to the Mars Sample Return mission comes just over a year after the first aircraft in history took powered flight on another planet, when NASA’s Ingenuity helicopter ascended to the Martian skies in April 2021. Since then, the experimental rotorcraft has taken 28 more flights, far surpassing expectations. 

“The whole point of Ingenuity was to be that Wright Brothers moment that leads to some future down the road of additional aerial exploration of Mars,” says Teddy Tzanetos, the Ingenuity Mars Helicopter Team Lead at NASA’s Jet Propulsion Laboratory. “Ingenuity’s goal was to make flying boring… Now we can just keep doing boring flights and doing exciting things with boring flights.”

Initially, the Mars Sample Return mission concept included a so-called fetch rover: A robot capable of collecting the samples already cached in tubes by the Perseverance rover. The fetch rover would have ferried them several hundred yards across the Martian surface to a lander near Jezero Crater, where the sample tubes would be transferred to the Mars Ascent Vehicle. The rocket-powered ascent vehicle would then launch the container with the sample tubes into orbit where a spacecraft with its sights set on returning to Earth would be waiting. 

But, says Ann Devereaux, who is the Mars Sample Return Deputy Program Manager, “getting a rover that was big enough and capable enough to go and do a reasonable job of collecting samples was problematic.” It would be costly to design and ship such a rover along with the Mars Ascent Vehicle.

The team was exploring other concepts right as Ingenuity took its first test flights. After the rotorcraft proved to be a success, the engineers began to study whether helicopters might be the best option for fetching the samples cached by Perseverance. 

[Related: This sailplane could cruise Mars for months on only wind]

Helicopters are smaller, lighter, and more nimble than rovers in many situations, Devereaux says. Although the aircraft need a secure place to land, they don’t have to worry about traversing dunes on weighty tires. 

Designs for the sample return helicopters won’t differ much from Ingenuity. “When you’re talking about robots in space, heritage is extremely important,” Tzanetos says. “We want to stick as close to Ingenuity design as we can because we know that it’s reliable, we know that it’s robust.”

Because Martian air is so thin—about 1 percent of the density of Earth’s—any aircraft on Mars has to be extremely lightweight and have large, fast-spinning rotor blades to provide sufficient lift, he explains. Ingenuity’s repeated flights confirmed NASA’s aerodynamic simulations were accurate–so much so the models will guide how engineers build the new pair of flying robots. 

The sample recovery helicopters won’t be an exact replica of Ingenuity, though. The team will have to make some tweaks, Tzanetos says, because these two rotorcraft will have to do more than just fly. They will need to travel about 2,300 feet from the lander to the cache depot site, pick up a tube, fly back to the lander, and drop it off in a designated drop-off site–and then repeat that cycle 15 times, he says. 

And that means the helicopters will have to support more weight than the 4-pound Ingenuity. The current concept design for the sample retrieval helicopters calls for additional tools, like arms to pick up samples and wheels to maneuver at the cache depot and drop sites, that could add another pound to the robots, according to Tzanetos.

“We’ve done the calculations, we figured out there’s certain changes we can make to the rotor system to get it to lift more mass,” he says. Now that the Mars Sample Return mission leaders have decided to go ahead with the fetch helicopter concept, Tzanetos and his team are focusing on making those tweaks. 

One of their first steps is to determine how much further they can push Ingenuity’s original rotor system. Just in case the Martian environment was more challenging than the team’s models predicted, the engineers designed the test helicopter to have more lift than thought necessary. 

“We’re starting to work on figuring out what is the optimal point where you trade off all of these different mass applications,” he says. “We can spin the blades slightly faster, we can demand more out of the rotor system, for example, and we can carry a heavier aircraft that allows us to accomplish the mission.”

The helicopters may not end up being needed at all, however. They will be flown to Mars just in case the Perseverance rover cannot deliver samples or the robot meets its demise before the retrieval is complete. 

But the future of helicopters on Mars may already be foretold by Ingenuity’s success. 

“This helicopter has been phenomenal,” Devereaux says, describing how Ingenuity proved it could fly in front of the Perseverance rover and scout ahead for the rover’s on-the-ground sleuthing. She adds that helicopters offer us an additional perspective of our neighboring planet. Perhaps one day a drone-like rotorcraft could swoop through canyons like those that make up Valles Marineris, revealing the geologic layers of the Red Planet up-close where rovers can’t go. 

“Rovers have now become common” for Martian exploration, Tzanetos says. “We understand how to build rovers, we understand how to operate rovers. I’m hoping that we will be saying the same thing about helicopters in the decades to come.” Perhaps fleets of aircraft, he says, with wings like planes or copter-like blades, will one day fill the Martian skies. 

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When Harvard’s Rohan Naidu saw the galaxy, the first thing he did was message his collaborator, Pascal Oesch, a cosmology professor at the University of Geneva in Switzerland. The second thing he did was call his girlfriend. 

“‘Would you like to be the second human being to see potentially the most distant galaxy ever known?’” Naidu recalls asking her. She looked, found it “a bit underwhelming,” he says, and went back to watching TV. “But she’s come around,” he says with a laugh. 

The galaxy candidate in question, GLASS-z13, doesn’t look like much to the untrained eye. Just a red splotch of light. But that unassuming visual is precisely why GLASS-z13 captured Naidu’s attention. It’s how he expects a galaxy that existed 13.5 billion years ago, one that is close to the limits of our ability to detect, to look from the vantage point of the James Webb Space Telescope (JWST). 

After the first batch of data from the JWST became public last week, Naidu, who is a postdoctoral researcher at the Center for Astrophysics | Harvard & Smithsonian, spent every waking hour filtering through the data to search for the most distant galaxies ever detected. He didn’t get a lot of sleep, but his efforts paid off. 

[Related: Hubble discovers a distant galaxy that might have closely followed the Big Bang]

On July 19, along with collaborators from around the globe, Naidu posted a paper in advance of expert review to the open access platform arXiv that describes two such candidate galaxies. He estimates one of these to be about 13.5 billion years old, making it the most distant galaxy ever detected. That would mean the system, GLASS-z13, was around perhaps as early as 300 million years after the Big Bang, which is thought to have occurred 13.8 billion years ago. As such, GLASS-z13 offers astronomers a never-seen-before view into the early days of the universe. And it is already challenging existing ideas about the earliest galaxies.

“I could not believe my eyes,” Naidu says of first seeing GLASS-z13 in the JWST data. He immediately noticed that it was bright and clear, which stood out as a bit of a surprise. “Even though the universe was so young, these things managed to have some kind of growth spurt and become so bright and so massive so quickly.” 

Naidu is careful to describe GLASS-z13 as a “candidate” galaxy, as the team’s analysis from the first batch of JWST data still needs to be validated by follow-up observations. However, on the same day that Naidu uploaded the study to arXiv, another team of researchers independently posted a report that describes the same galaxy candidates—and also places them as the most distant galaxies we’ve ever seen.

“If two independent groups see that, it gives confidence,” says Renske Smit, an astrophysicist at Liverpool John Moores University in England who was not involved in either paper. Still, she says, “I think we need unambiguous confirmation that these galaxies were formed so early in the universe.”

That confirmation, Smit says, will come from subsequent JWST observations that look more closely at the spectrum of light coming from GLASS-z13. 

Naidu and his colleagues initially determined the distance of the galaxy candidate by looking at that patch of sky in several different infrared wavelengths. As light travels through time and space, its wavelengths are stretched out to be longer. Their light, therefore, appears redder, in what is called a “redshift.” A galaxy that is far, far away will appear to us to be redder than a similar galaxy nearby. The scientists estimated how far the light from GLASS-z13 had traveled by estimating how much it had likely shifted. 

JWST, much like a pair of night goggles, is designed to pick up weak heat signatures found in the longer, infrared wavelengths of light. But that means the telescope also finds old, dead, or dying galaxies. Because these galaxies are cooler than young ones, they can also appear quite red, even when nearby, says Brooke Simmons, an associate professor of astrophysics at Lancaster University who was not involved in the new paper. But Simmons says she thinks the study authors have done “a reasonable job” trying to account for this; if the system was from the “middle-aged part of the universe,” she says, “we would be still be able to see it with the bands [of light] that are shorter wavelengths and we don’t.”

But the redness of GLASS-z13 wasn’t Naidu’s only clue indicating the galaxy candidate was extremely far away. He also noticed something missing: the bluest photons. 

In the very early universe, “oceans of neutral hydrogen” soaked up the deepest-blue photons, leaving behind only particles at redder wavelengths, Naidu explains. And the missing photons correspond to those that hydrogen absorbs, he says, suggesting that the light JWST saw from GLASS-z13 is indeed emanating from the earliest parts of the universe. 

Naidu and his colleagues are already working to get time on JWST to make the necessary follow-up observations to confirm their estimates. The next observations will look at specific parts of the spectrum of light coming from GLASS-z13. This will allow them to more precisely measure the galaxy candidate’s redshift. 

Characteristics of GLASS-z13 are already raising new questions for astrophysicists who study the early days of the cosmos. Primarily, its remarkable brightness and mass has caught the attention of scientists. They estimate that it is approximately 1 billion times the mass of our sun. 

“How do you get all the stars in there so quickly? We think it takes time to build up a galaxy that’s massive enough, that has enough stars for it to be so bright,” Smit says. “And so either stars might start forming earlier than we thought, or maybe these galaxies have somehow a way of forming stars really, really quickly. We don’t quite know yet.”

[Related: Rare ‘upside-down stars’ are shrouded in the remains of cannibalized suns]

Some scientific models also predicted that galaxies like this would be extremely rare, Naidu says. “But here, we found two of them, not too far away from each other.”

The other galaxy candidate described in Naidu’s paper, called GLASS-z11, is probably slightly less far away from Earth than GLASS-z13. It also adds a curious detail: It shows hints of moving into a spiral disk formation. 

“We didn’t expect disk galaxies to form so early,” Simmons says. “A few hundred million years is a very short time. A lot of us expected a lot of turbulence, a lot of chaos, a lot of stuff just assembling in an area that has a little bit more mass and so has a little bit stronger gravity and it just gobbles up everything around it, not necessarily in the kind of ordered structure that you would need to form a coherently rotating disk.” 

This discovery, about a week after the first data from JWST, is just the start. “These are not the very first stars or galaxies,” Smit says. “We could expect a lot more record-breaking galaxies in the years to come. I think we’re going to see stuff even much farther away, much older, that were stars that formed closer to the big bang.”

Correction (July 22, 2022): The story has been updated to reflect that Pascal Oesch is now at the University of Geneva, not Yale University.

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Gravity is everywhere. It’s the force that anchors the Earth in its orbit around the sun, stops trees from growing up forever, and keeps our breakfast cereal in its bowl. It’s also an essential component in our understanding of the universe. 

But just how strong is the force? We know that gravity acts the same whether an object is as light as a feather or as heavy as a stone, but otherwise, scientists don’t have a precise answer to that question, despite studying gravity in the cosmos for centuries. 

According to Isaac Newton’s law of universal gravitation, the gravitational force drawing two objects (or particles) together gets stronger the more massive those objects are and the closer they get to each other. For example, the gravity between two feathers that are five inches apart is weaker than two apples that are the same distance from one another. However, the exact calculation of the force relies on a universal variable called the gravitational constant, which is represented by “G” in equations. 

[Related: The standard model of particle physics might be broken]

Physicists don’t know exactly what value to assign to “G.” But a new approach from Switzerland might bring fresh insights on how to test better for gravity in the first place.

“These fundamental constants, they are basically baked into the fabric of the universe,” says Stephan Schlamminger, a physicist in the Physical Measurement Laboratory at the National Institute of Standards and Technology. “Humans can do experiments to find out their value, but we will never know the true value. We can get closer and closer to the truth, the experiments can get better and better, and we approximate the true value in the end.”

Why is “G” so difficult to measure?

Unlike counting, measuring is inherently imprecise, says Schlamminger, who serves as chair of the Working Group on the Newtonian Constant of Gravitation of the International Union of Pure and Applied Physics.

“If you take a tape measure and measure the length of a table, let’s say it falls between two ticks. Now you have to use your eye and figure out where [the number] is,” he says. “Maybe you can use a microscope or something, and the more advanced the measurement technique is, the smaller and smaller your uncertainty will become. But there’s always uncertainty.”

It’s the same challenge with the gravitational constant, Schlamminger says, as researchers will always be measuring the force between two objects in some form of increments, which requires them to include some uncertainty in their results.

On top of that, the gravitational force that can be tested between objects in a lab will always be limited by the size of the facility. So that makes it even trickier to measure a diversity of masses with sophisticated tools.

Finally, there can always be interference in readings, says Jürg Dual, a professor of mechanics and experimental dynamics at ETH Zurich, who has conducted a new experiment to redetermine the gravitational constant. That’s because any object with mass will exert a gravitational pull on everything else with mass in its vicinity, so experimenters need to be able to remove the external influence of Earth’s gravity, their own, and all other presences that hold weight from the test results.

What experiments have physicists tried?

In 1798, Henry Cavendish set the standard for laboratory experiments to measure the gravitational constant using a technique called the torsion balance. 

That technique relies on a sort of modified pendulum. A bar with two test masses on each end is suspended from its midpoint on a thin wire hanging down. Because the bar is horizontal to the Earth’s gravitational field, Cavendish was able to remove much of the planetary force from the measurements. 

Cavendish used two small lead spheres two inches in diameter as his test masses. Then he added a second set of masses, larger lead balls with a 12-inch diameter, which were hung separately from the test masses but near to each other. These are called the “source” masses. The pull of these larger lead balls causes the wire to twist. From the angle of that twist, Cavendish and his successors have been able to calculate the gravitational force acting between the test and the source masses. And because they know the mass of each object, they are able to calculate “G.” 

Similar methods have been used by experimenters in the centuries since Cavendish, but they haven’t always found the same value for “G” or the same range of uncertainty, Schlamminger says. And the disagreement in the uncertainty of the calculations is a “big enigma.”

So physicists have continued to devise new methods for measuring “G” that might one day be able to reach a more precise result. 

[Related: From the archives: The Theory of Relativity gains speed]

Just this month, a team from Switzerland, led by Dual, published a new technique in the journal Nature Physics, which may cut out noise from surroundings and produce more accurate results.

The experimental setup included two meter-long beams suspended in vacuum chambers. The researchers caused one beam to vibrate at a particular frequency; due to the gravitational force between the two beams, the other beam would then begin to move as well. Using laser sensors, the team measured the motion of the two beams and then calculated the gravitational constant based on the effect that one had on the other. 

Their initial results yielded a value for “G” that is about 2.2 percent higher than the official value recommended by the Committee on Data for Science and Technology (which is 6.67430×10⁻¹¹ m^3⋅kg⁻¹s⁻²), and holds a relatively large window of uncertainty. 

“Our results are more or less in line with previous experimental determinations of ‘G.’ This means that Newton’s law is also valid for our situation, even though Newton didn’t ever think of a situation like the one we have presented,” Dual says. “In the future, we will be more precise. But right now, it’s a new measurement.”

This is a slow-moving but globally collaborative endeavor, says Schlamminger, who was not involved in the new research. “It’s very rare to get a paper on big ‘G,’” so while their results may not be the most precise measurement of the gravitational constant, “it’s exciting” to have a new approach and another measurement added to one of the universe’s most weighty mathematical constants.

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Dante Lauretta didn’t expect the surface of the asteroid to be, as he puts it, “fluffy.”

As NASA’s OSIRIS-REx spacecraft descended toward asteroid Bennu to grab a sample of its surface materials, mission principal investigator Lauretta and his team knew the process would leave a mark–both on planetary science and on the boulder-filled surface of the rock itself. For its first-ever mission to retrieve a sample from an asteroid, the space agency selected a target that holds leftover, unchanged material from when the solar system formed.. 

“We had thought we were going to dig, at most, a little 30-centimeter pit,” says Lauretta, who is also a regents professor at the University of Arizona’s Lunar and Planetary Laboratory. Instead, he says, the material on the surface of Bennu was so loose, “we blew a hole eight meters wide on the surface.” (That’s a crater stretching more than 20 feet across.)

After examining that October 2020 touch-down in detail, planetary scientists determined that the material on the surface of Bennu must be fairly loosely packed, kind of like a dust bunny, Lauretta says. The details are described in a pair of papers published this week in the journals Science and Science Advances.

[Related on PopSci+: In its visit to Psyche, NASA hopes to glimpse the center of the Earth]

This information will be of great importance next year, when OSIRIS-REx delivers a sample of Bennu back to Earth for scientists around the world to study more closely. The goal for the sample-return mission is to shed light on the origins of our corner of the solar system, perhaps even revealing the chemistry that led to the evolution of life on Earth. The asteroid’s contents are particularly unique because they never underwent the same property-changing processes as rocks from planets like Mars.

“Any geologist worth their salt would say, ‘you can’t really understand a rock until you know where it came from.’ Where was the host rock? What was the surrounding environment?” Lauretta explains. “That’s exactly what OSIRIS-REx has done with our sample site.”

And that means figuring out just how “fluffy” the surface of Bennu might be. The team behind the mission determined the bulk density of Bennu’s surface material (the layer on rocky orbiting bodies called “regolith”) using two different approaches. Lauretta and his collaborators analyzed images taken of the sampling site before and after the spacecraft touched down, the results of which are described in the Science paper. Meanwhile, Kevin Walsh, the lead researcher for the Regolith Development Working Group on the mission and a scientist at the Southwest Research Institute, analyzed the force that the asteroid exerted against the car-sized spacecraft—in other words, just how soft of a landing did OSIRIS-REx experience. Those results are described in the Science Advances paper.

[Related: NASA is winding up to punch an asteroid]

The answer, they both found separately, was that it was a startlingly soft landing. While the average rock has a density of about 3,000 kilograms per cubic meter, Lauretta says, the surface material on Bennu has a bulk density of about 500 to 700 kilograms per cubic meter.

Another metric that the scientists looked at was the cohesion of Bennu’s regolith—how strongly different particles stick together, like clumps of flour or cocoa powder, Walsh explains. His analysis revealed “there was essentially no cohesive bonding of the surface [material].” 

When OSIRIS-REx landed on Bennu, the spacecraft was performing a maneuver new to NASA: It briefly kissed the asteroid with a robotic arm, called the “Touch-and-Go Sample Acquisition Mechanism” (TAGSAM), blasted a small amount of nitrogen gas at the surface material to stir it up, and then sucked some dust, grains, and pebbles into a sample collection vessel to be returned to Earth. 

“As soon as the gas released, there was stuff everywhere,” Walsh says, describing watching video taken of the touchdown. “It was like a hurricane,” he recalls, with loose grains and rock fragments billowing up around the TAGSAM arm.

The descent itself proved to be challenging, given that the regolith wasn’t dense enough to push back on the landing spacecraft. “If we hadn’t fired the thrusters to start backing away from the asteroid, I think we would have gone all the way in and disappeared, like quicksand,” Lauretta says.

OSIRIS-REx discovered water locked in the clays on Bennu, so Lauretta thinks it’s possible that the asteroid’s boulders themselves are porous and not fixed together. Think of it like a day-old drip castle made from dried-out sand at the beach. If disrupted by a small force (human feet or the wind), it could easily collapse into a loose pile of sediment. 

[Related: Local asteroid Bennu used to be filled with tiny rivers]

Once the samples return to Earth in September 2023, scientists will get a chance to test why Bennu’s regolith is so loose—and then some. The material will go through a “whole battery of tests,” Lauretta says; it will be studied in labs across four different continents for mineralogy and chemistry, different isotopes to determine the asteroid’s age, and organic molecules and volatiles like water that could shed life on how Earth became habitable. Perhaps an asteroid like Bennu delivered water to our planet at a critical moment in its development.

The sample from Bennu won’t be the first space rock to be studied in such fine detail. Meteorites that have broken off of other planetary bodies and hurtled to Earth’s surface have been the subject of scientific scrutiny for decades. But those rocks are contaminated and possibly even altered by our planet’s atmosphere, which makes it tough to pinpoint where they came from. “They’re random samples from space with no context,” Lauretta says. 

Pristine samples have to be obtained directly from their source and carefully protected on their trip through Earth’s atmosphere. While the OSIRIS-REx mission will be NASA’s first time bringing rocks back from an asteroid, the Japanese Aerospace Exploration Agency (JAXA) recently conducted a similar mission, Hayabusa2, on the asteroid Ryugu. A previous JAXA probe, Hayabusa, targeted Itokawa, a stonier asteroid. When the samples returned in 2010, the team thought it had failed to return any material. But after opening the collector, they found a few rocky particles. Ultimately, all three missions will provide crucial data for a model of what the early solar system might have looked like.

OSIRIS-REx also has a second destination after Bennu. When the spacecraft returns to Earth, it will drop the sample return capsule to a site in the Utah desert via parachute. The rest of the probe will continue on an extended mission called OSIRIS-APEX to orbit another near-Earth asteroid, Apophis.

OSIRIS-APEX won’t collect any samples from the space rock, but will study the asteroid for 18 months from orbit. It will also perform a maneuver similar to the sample-return one, where it will get close to Apophis’s surface and fire its thrusters to expose what’s directly underneath. That process could reveal that “fluffy” surfaces like Bennu’s are more of a rule than an exception.

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Somewhere in the universe, there may be rocky worlds perhaps twice as distant from their host stars as Earth is from the sun. So far from their stars’ warmth, these planets should be quite cold—and any water on their surfaces should be frozen. 

But planetary scientists say there could be a class of rocky exoplanets covered in thick blankets of hydrogen and helium gases. If those layers insulate the planets’ cores from the harsh chill of space, their surfaces might be just the right temperature to host liquid water. And, if that’s the case, it’s possible that these worlds are habitable.

About a decade ago, scientists proposed that such worlds might be able to support life. They sometimes refer to these planets as “cold super-Earths,” because they’re probably up to 10 times more massive than our home. But the researchers hadn’t figured out whether water could stick around on these exoplanets long enough for life to evolve. 

Now, new calculations described in a paper published Monday in the journal Nature Astronomy suggest that the surface conditions of these worlds could have been temperate for more than enough time for life—for 5 billion to 8 billion years. Earth is only about 4.5 billion years old, by comparison, and life emerged here about 3.7 billion years ago. 

“Life needs some time to evolve. So it does matter that it has been a long period,”  says Björn Benneke, a professor of astrophysics at the Institute for Research on Exoplanets at the University of Montreal who was not involved in the new study. If super-Earths only had liquid water for relatively small slices of their existence–for instance, a million years or so–it would be “discouraging” for the hypothesis that these planets may be habitable beneath hydrogen atmospheres, he says.

The new calculations bode well for the potential habitability of these cold super-Earths. Their existence is still theoretical—none have been found yet—so this adds an incentive for astrophysicists to hunt for this exoplanet class as they seek to determine whether we’re alone in the universe. 

[Related: NASA’s official exoplanet tally has passed 5,000 worlds]

“It’s important to be really open-minded, and not to expect that life has to be under conditions that are just a copy of exactly Earth,” says Marit Mol Lous, lead author on the new paper and a PhD student studying exoplanets at the University of Zurich in Switzerland. “This gives us an extra argument to keep these exotic habitats in mind.”

Based on our only model of a known-habitable world, Earth, scientists often look for a planet that also orbits its star in a region where the planet’s surface is neither too hot nor too cold for liquid water. That region is often called the habitable zone, or nicknamed the “Goldilocks zone.” So-called cold super-Earths, in contrast, lie beyond their stars’ habitable zone. But that might also, counterintuitively, be part of what makes those alien worlds habitable. 

On Earth, atmospheric greenhouse gases such as carbon dioxide and methane help maintain that “just right” temperature for water. Hydrogen can also act as a greenhouse gas, if there’s enough of the stuff around.

The trick is keeping that hydrogen gas around long enough for it to build up. It’s a particularly light element, so unless a planet is massive enough and has enough gravity to hold onto the gas, hydrogen will vanish into space.  And if the planet is close to its star, the radiation can make those particles escape more quickly. The vast distance between these cold super-Earths and their stars could protect their hydrogen gas from being torn away.

To figure out what it would take for a cold super-Earth to maintain just the right thickness of a hydrogen-helium atmosphere over an extended period of time, Mol Lous developed computer models of various sized rocky exoplanets. She placed them at multiple distances from their simulated host stars. Then, she ran a simulation of how they might evolve over time. 

Mol Lous considered factors that would affect a planet’s surface temperature such as the rate of escape, how its host star might brighten or dim over time, and the heat emanating from radioactive material in its interior. 

[Related: On this blisteringly hot metal planet, a year lasts only 8 hours]

She found that the sweet spot for long-term liquid water was if the hydrogen-helium dominated atmosphere was between 100 and 1,000 times as thick as Earth’s atmosphere, the planet’s mass was one to 10 times that of the Earth’s, and it sat at least two times as far from its star as Earth does the sun. 

That distance, while it makes these cold super-Earths intriguing to study, it also makes them extremely difficult for astronomers to spot. The technique that scientists usually use to detect an exoplanet relies on the world passing in front of its star. Such a transit makes the host star’s light dim slightly, which astrophysicists use to calculate the presence of an orbiting world. But, says Benneke, when a super-Earth-sized planet is orbiting so far out, it is much less likely to be aligned at the right moment to be detectable with current technology. 

As such, it’s still unknown whether such super-Earths exist, he says. “But … what experts have shown is that this kind of diversity of planets, the whole range of planets that can exist is actually extremely big.” And if they do exist, many questions remain about how such a chilly, wet world might come to be. Mol Lous and her colleagues are already working on new models to explore the formation of cold super-Earths. 

But the best solution to these mysteries, Benneke says, “would be to simply find these exoplanets.”

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When a star 20 times as massive as our sun dies, it can explode in a supernova and squeeze back down into a dense black hole (with gravity’s help). But that explosion is never perfectly symmetrical, so sometimes, the resulting black holes goes hurtling off into space. These wandering objects are often called “rogue black holes” because they float around freely, untethered by other celestial bodies. 

But that name might be a “misnomer,” according to Jessica Lu, associate professor of astronomy at the University of California Berkeley. She prefers the term “free-floating” to describe these black holes. “Rogue,” she says, implies that the nomads are rare or unusual—or up to no good.

That’s certainly not the case. Astronomers estimate that there are as many as 100 million such black holes that roam around our galaxy. But because they’re solitary, they’re extremely difficult to find. Until recently, these so-called rogue black holes were only known through theory and calculations. 

“They are ghosts, so to speak,” says Lu, who has made it her mission to find the Milky Way’s free-floating black holes. 

[Related: We’re still in the dark about a key black hole paradox]

Earlier this year, two teams of space researchers separately revealed detections of what just might be one of these roaming black holes. One of those teams was led by Casey Lam, a graduate student in Lu’s lab. The other was led by Kailash C. Sahu, an astronomer at the Space Telescope Science Institute. Both teams posted their papers on an open-access website without expert review.

The scientists will get more data from the Hubble Space Telescope in October that Lu says should help “resolve the mystery of whether this is a black hole or a neutron star.” “There’s still a lot of uncertainty about how stars die and the ghost remnants that they leave behind,” she notes. When stars much more massive than our sun run out of nuclear fuel, they’re thought to collapse into either a black hole or a neutron star. “But we don’t know exactly which ones die and turn into neutron stars or die and turn into black holes,” adds Lu. “We don’t know when a black hole is born and a star dies, is there a violent supernova explosion? Or does it directly collapse into a black hole and maybe just give a little burp?” 

With star stuff making up everything we know in the world, understanding the afterlife of stars is key to understanding how we, ourselves, came to be.

How to spot a black hole on the loose

Black holes are inherently invisible. They trap all light that they encounter, therefore there’s nothing for the human eye to perceive. So astronomers have to get creative to detect these dense, dark objects. 

Typically, they look for anomalies in gas, dust, stars, and other material that might be caused by the intensely strong gravity of a black hole. If a black hole is tearing material away from another celestial body, the resulting disk of debris that surrounds the black hole can be brightly visible. (That’s how astronomers took the first direct image of one in 2019 and an image of the black hole at the center of the Milky Way earlier this year.)

But if a black hole is not inflicting chaos with its gravitational force, there’s hardly anything to detect. That’s often the case with these moving black holes. So astronomers like Lu use another technique called astrometric or gravitational microlensing.

“What we do is we wait for the chance alignment of one of these free-floating black holes and a background star,” Lu explains. “When the two align, the light from the background star is warped by the gravity of the black hole [in front of it]. It shows up as a brightening of the star [in the astronomical data]. It also makes it take a little jaunt in the sky, a little wobble, so to speak.”

The background star doesn’t actually move—rather, it appears to shift off its course when the black hole or another compact object passes in front of it. That’s because the gravity of the black hole warps the fabric of spacetime, according to Albert Einstein’s General Theory of Relativity, which alters the starlight.

Astronomers use microlensing to study all kinds of temporary phenomena in the universe, from supernovae to exoplanets transiting around their stars. But it’s tricky to do with ground-based telescopes, as the Earth’s atmosphere can blur the images. 

“In astrometry, you’re trying to measure the position of something very precisely, and you need very sharp images,” Lu explains. So astronomers rely on telescopes in space, like Hubble, and a couple of ground-based instruments that have sophisticated systems to adapt for the atmospheric interference. “There are really only three facilities in the world that can make this astrometric measurement,” Lu says. “We’re working right at the cutting edge of what our technology can do today.”

The first rogue black hole? 

It was that brightening, or a “gravitational lensing event” as Lu calls it, that both her and Sahu’s teams spotted in data from the Hubble Space Telescope in 2011. Something, they surmised, must be passing in front of that star.

Figuring out what caused the wobble and change of intensity in a star’s light requires two measurements: brightness and position. Astronomers observe that same spot in the sky over time to see how the light changes as the object passes in front of the star. This gives them the data they need to calculate the mass of that object, which in turn determines whether it’s a black hole or a neutron star. 

“We know the thing that’s doing the lensing is heavy. We know it’s heavier than your typical star. And we know that it’s dark,” Lu notes. “But we’re still a little uncertain about exactly how heavy and exactly how dark.” If it’s only a little bit heavy, say, one and a half times the mass of our sun, it might actually be a neutron star. But if it’s three to 10 times as massive as our sun, then it would be a black hole, Lu explains.

As the two teams gathered data from 2011 to 2017, their analyses revealed distinctly different masses for that compact object. Sahu’s team determined that the roaming object has a mass seven times that of our sun, which would put it squarely in black hole territory. But Lam and Lu’s team calculated it to be less massive, somewhere between 1.6 and 4.4 solar masses, which spans both possibilities. 

[Related: Black holes can gobble up neutron stars whole]

The astronomers can’t be sure which calculation is correct until they get a chance to know just how bright the background star is normally and its position in the sky when something isn’t passing in front of it. They weren’t focused on that star before noticing its uncharacteristic brightness and wobble, so they’re just now getting the chance to make those baseline observations as the lensing effect has faded, Lu explains. Those observations will come from new Hubble data in the fall.

What they do know is that the object in question is in the Carina-Sagittarius spiral arm of the Milky Way galaxy, and is currently about 5,000 light years away from Earth. This detection also suggests that the nearest roaming black hole to could be less than 100 light years away, Lu says. But that’s not reason for concern.

“Black holes are a drain. If you get close enough, they will consume you,” Lu points out. “But you have to get very close, much closer than I think we typically picture.” The boundary around a black hole marking the line where light can still escape its gravity, called the event horizon, typically has a radius of under 20 miles.

The odds that a roaming black hole could pass through our celestial neighborhood and disrupt life on Earth are “astronomically small,” Lu says. “That’s the size of a city. So a black hole could pass by the solar system and we’d hardly notice.”

But she’s not ruling it out. “I’m a scientist,” she says. “I can’t say no chance.”

Regardless of whether the first teams detected a roaming black hole or a neutron star, Lu says, “the real revolution that these two papers are showing is that we can now find these black holes using a combination of brightness and position measurements.” This opens the door to discoveries of more light-capturing nomads, especially as new telescopes come online, including the Vera C. Rubin Observatory currently under construction in Chile and the Nancy Grace Roman Space Telescope scheduled to launch later this decade.

The way Lu sees it, “the next chapter of black hole studies in our galaxy has already begun.”

The post ‘Rogue black holes’ might be neither ‘rogue’ nor ‘black holes’ appeared first on Popular Science.

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A one-of-a-kind meteorite from Mars has an unexpected chemistry that could refine scientists’ models of how terrestrial planets form, according to a new study of the old space rock. 

Chemical clues from this far-flung sample hint that Mars and Earth–often viewed as would-be twins because they are rocky worlds and solar system neighbors–were birthed in very different ways: Earth formed slowly, and Mars much faster.

Current hypotheses about the creation of a rocky planet, like Mars or Earth, suggest that some elements in the planet’s interior should have the same chemical characteristics as those in the planet’s atmosphere. That’s because, in the early days of our solar system about 4.5 billion years ago, the rocky planets were covered in a magma ocean. As the planets cooled and their molten mantles solidified, the process probably released the gasses that became atmospheres. 

Those gasses weren’t just any chemicals. They were volatiles, chemical elements and compounds that vaporize very easily. Volatiles include hydrogen, carbon, oxygen, and nitrogen, as well as noble gasses, which are inert elements that don’t react with their environment. On Earth, those chemicals eventually allowed our world to develop and support life.

To look for signs of that process on Mars, Sandrine Péron, a postdoctoral fellow in the Institute of Geochemistry and Petrology at ETH Zürich compared two Martian sources of the noble gas krypton. One source was a meteorite that originated in the Martian interior. The other was  krypton isotopes sampled from Mars’ atmosphere by NASA’s Curiosity Rover. Unexpectedly, the krypton signatures did not match. And that could change the sequence of events for how Mars got its volatiles and atmosphere in the first place.

“This is kind of the opposite to the standard model of volatile accretion,” Péron says. Her results are described in a paper published Thursday in the journal Science. “Our study shows that it’s a bit more complicated.”

The planets in our solar system formed from the debris of our sun’s birth. Clumps of material coalesced in the swirling disk of gas and dust, called a solar nebula, around the new star. Some clumps, which accumulated through gravity and collisions, grew large enough to become planets and develop complex geological processes. Others remained small and inactive as primitive asteroids and comets. 

[Related: Mysterious bright spots fuel debate over whether Mars holds liquid water]

Scientists think that volatiles were first incorporated into the new worlds directly from the solar nebula in the earlier stages of planetary development. Later, as the solar nebula dissipated, more volatiles were delivered from bombardments of chondritic meteorites, small chunks of stony asteroids that remain unchanged from the earliest days of the solar system. Those meteorites then melted into the magma oceans.

If the atmosphere was delivered by space rock, planetary scientists would expect the volatiles in a planet’s atmosphere to match those from chondritic meteorites, not the solar nebula. Instead, Péron found that the krypton from the Martian interior is nearly purely chondritic, while the atmosphere is solar. 

As such, perhaps Mars was bombarded by chondritic meteorites early on and then solidified while there was still enough solar nebula to form an atmosphere around the hardened Red Planet, Péron suggests. She explains that the nebula would have dissipated around 10 million years after the sun formed, so the accretion of Mars would have had to be completed well before then, perhaps in the first 4 million years. 

“It looks like Mars acquired its atmosphere from the primordial gas that permeated the solar system as it was forming,” says Matt Clement, a postdoctoral fellow studying terrestrial planet formation at the Carnegie Institution for Science who was not involved in the study. “This generally fits in with our picture. We think Mars formed much, much faster than the Earth did.”

Scientists often look to Mars to study the early solar system precisely because of how fast it is thought to have formed. Mars, which is a tenth of the mass of Earth, is also far less geologically active, which means the Red Planet probably preserves a lot of the conditions of our planetary neighborhood’s earliest days. 

However, to study the chemistry of Mars, scientists either have to send mechanical envoys like the Curiosity Rover to the planet or examine pieces of Mars that have broken off, hurtled through space, and landed on the surface of Earth. There are only a few hundred such meteorites.

The meteorite that Péron studied is unique. In 1815, it plummeted through Earth’s atmosphere, fracturing into pieces over Chassigny, France. Since then, scientists studying the fragments of the Chassigny meteorite determined that it likely came from the Martian interior—unlike all other Mars meteorites. 

This study highlights how much there is still to learn about planetary formation, Clement says. “We still don’t really understand fully where the volatiles on our own planets and the closest couple planets to us came from,” he says. “The further we dig into the formation of the planets we can measure the best, the more complicated that process seems to be.”

Each new distinction between Earth and Mars hints at even more diversity among planets elsewhere, Clement adds. “If it’s that easy to form planets that are that different so close to each other,” he says, what weird worlds might scientists find orbiting other stars?

The post How did Mars get its gasses? A special space rock holds clues. appeared first on Popular Science.

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Emanating from deep in space, massive explosions show up in astronomers’ data as a quick surge of radio waves. Fast radio bursts (FRBs), as they’re called, can carry as much energy in a single pulse as our sun emits in 100 years. But, because the bursts often last just a few thousandths of a second, radio astronomers typically have insufficient context to make sense of these dramatic cosmic events or determine where exactly the flashes originated. As such, FRBs have been one of astronomy’s great mysteries. 

Scientists don’t know a lot about what causes these violent eruptions of radio waves. Some theorists posit that the explosions emanate from the collision of extremely dense objects like black holes or neutron stars. Others suggest FRBs come from the collapse of distant stars. 

Now, astronomers are accruing the evidence they need to put the pieces of the FRB puzzle together—a newly spotted burst has two key attributes that might help astronomers take a more sustained look at these enigmatic explosions. 

The latest FRB detection comes from the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in Guizhou, China. But this explosion was more than just one flash in astronomers’ data. It repeats sporadically, so researchers were able to locate it in follow-up observations at telescopes around the world. Described in a paper published in the journal Nature this week, FRB 20190520B is also associated with a persistent source of radio emissions between those bursts. The source sits at the edge of a dwarf galaxy roughly 3 billion light-years from Earth.

To make sense of FRBs, researchers have been searching for events like this one—that repeat. “The key question for everybody is its origin story,” says study author Di Li, the chief scientist of the FAST telescope who leads the radio division of ​​the National Astronomical Observatories of the Chinese Academy of Sciences. “We really want to know what kind of astronomical object or what kind of physics may produce such a bright thing.”  

The vast majority of FRBs that astronomers have detected since they were first discovered in 2007 have been distinct, individual events. Of more than 500 bursts that have been spotted, only about 5 percent repeat. 

The majority that don’t repeat pose an added challenge for follow-up study. “Although they are very bright, they are a one-off event,” Li says. “By the time you dig it out of the data, it could be the next day or even the next month. And then you just cannot go back … you cannot catch this cosmic explosion in the act.”

A single-time event is intriguing. But repetition is where researchers begin to puzzle out patterns for a deeper understanding of phenomena.

That’s why the latest FSB discovery offers a chance for researchers to put together the pieces of this bursting puzzle. This is only the second time that a repeating FSB has been detected with a persistent source of weaker radio waves between the pulses, following one that was initially spotted in 2012. Other repeaters have been detected since then, but no others have been associated with a persistent radio source, which offers astronomers more texture to study. 

“The first only poses more questions. It’s the second, and third, and fourth that help us get the answers to that question,” says Navin Sridhar, an astrophysics PhD candidate at Columbia University who studies FRBs and conducts simulations to determine the physics of such phenomena. He was not involved in the new study. “These are an extremely new class of events, and every single additional source and data point is just golden.”

Scientists are trying to sort out what engine drives these violent explosions–and just how many different things might cause FRBs. Part of that endeavor is identifying where in the cosmos the bursts originate, but researchers are also grouping the phenomena into different classes. Right now, they’re largely separated into repeaters and non-repeaters. The association of the persistent radio emission adds another wrinkle.

[Related: Astronomers spot repeating radio burst patterns from deep space]

With this new detection, “we can say confidently that [the FRB discovered in 2012] is not an outlier,” Sridhar says. But the parallel FRBs might represent an entire, distinct category of explosions. “So we cannot really put all FRBs into one basket and say, ‘Okay, all FRBs behave this way.’ This indicates the birth of a new class of FRBs.” 

Perhaps there might be another explanation, Li suggests. These two repeaters might be younger FRBs, he says. The idea centers around what you would expect to see right after an explosion. The debris doesn’t immediately dissipate. It takes a little while for that material to expand out into the cosmos. If astronomers spot the bursts early on, that denser cloud of ejecta could be the source of those persistent radio emissions. That would also explain why it’s so active, Li says. 

Although the new FRB detection has key similarities to the first repeating FRB detected in 2012, it is not precisely the same, Sridhar says. Furthermore, he says, that theory about these bursts being particularly young relies on assumptions about what is driving them. If a magnetar (a neutron star with an extremely strong magnetic field) is responsible, he says, that would make sense. But if the source was, say, a class of blackhole binaries that accrete matter from nearby stars, it could also reveal this radio signature—and it would get stronger over time.

“We really need to know what the environment of a FRB is in order to pin down the engine that is powering it,” Sridhar says. 

After all, explosions of radio waves aren’t rare. Scientists have calculated that hundreds of FRBs occur every day in the universe that are detectable on Earth. But researchers are only just beginning to scratch the surface in understanding this enigmatic phenomenon. And FRBs aren’t the only cosmic mystery.

“We live in this very dynamic universe,” Li says. “We keep finding these weird, sometimes hard to understand, mysterious things. There are way more things in the universe that are unknown than what has already been known.”

Correction (June 27, 2022): The story previously stated that the fast radio burst recently detected in China repeats at regular intervals, when it actually repeats sporadically. It has been corrected.

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