Fresh intel from Mars is sure to stir debate about whether liquid water lurks beneath the planet’s polar ice.
New data from a probe orbiting Mars appear to bolster a claim from 2018 that a lake sits roughly 1.5 kilometers beneath ice near the south pole (SN: 8/18/18). An analysis of the additional data, by some of the same researchers who reported the lake’s discovery, also hint at several more pools encircling the main reservoir, a study released online September 28 in Nature Astronomy claims.
If it exists, the central lake spans roughly 600 square kilometers. To keep from freezing, the water would have to be extremely salty, possibly making it similar to subglacial lakes in Antarctica. “This area is the closest thing to ‘habitable’ on Mars that has been found so far,” says Roberto Orosei, a planetary scientist at the National Institute for Astrophysics in Bologna, Italy, who also led the 2018 report.
Ali Bramson, a planetary scientist at Purdue University in West Lafayette, Ind., agrees “something funky is going on at this location.” But, she says, “there are some limitations to the instrument and the data…. I don’t know if it’s totally a slam dunk yet.”

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Orosei and colleagues probed the ice using radar on board the European Space Agency’s Mars Express orbiter. Short bursts of radio waves reflect off the ice, but some penetrate deeper and bounce off the bottom of the ice, sending back a second echo. The brightness and sharpness of that second reflection can reveal details about the underlying terrain.
The possible lake was originally found using radar data collected from May 2012 to December 2015. Now, in data collected from 2010 to 2019, the team once again found regions beneath the ice that are highly reflective and very flat. They say their findings not only confirm earlier hints of a large buried lake but also unearth a handful of smaller ponds encircling the main body of water and separated by strips of dry land.
“On Earth, there would be no debate” that a bright, flat radar reflection would be liquid water, Orosei says. These same analysis techniques have been used closer to home to map subglacial lakes in Antarctica and Greenland.
While much about these putative ponds remains unknown, one thing is certain: This new report is bound to spark controversy. “The community is very polarized,” says Isaac Smith, a planetary scientist with the Planetary Science Institute who is based in Ontario, Canada. “I’m in the camp that leans towards believing it,” he adds. “They’ve done their homework.”
One question centers on how water could stay liquid. “There’s no way to get liquid water warm enough even with throwing in a bunch of salts,” says planetary scientist Michael Sori, also at Purdue.
In 2019, he and Bramson calculated that the ice temperature — about –70° Celsius — is too cold even for salts to melt. They argue some local source of geothermal heat is needed, such as a magma chamber beneath the surface, to maintain a lake. That in turn has led to other questions about whether contemporary Mars could supply the necessary heat.
Smith — as well as the paper’s authors — thinks this isn’t a problem. As recently as 50,000 years ago, Smith says, the Martian south pole was warmer because the planet’s tilt (and hence its seasons) is constantly changing. Warmer temperatures could have propagated through the ice to create pockets of salty liquid. Alternatively, the ponds may have been there before the ice cap formed. Either way, at very high salt concentrations, once water has melted, it’s hard to get it to freeze again. “The melting temperature is different than the freezing temperature,” he says.
Even so, such liquid may be unlike any that most earthlings are familiar with. “Some supercooled brines at these cold temperatures are still considered liquid but turn into some weird glass,” Bramson says.
Resolving these questions will probably require more than radar. Multiple factors, such as the composition and physical properties of the ice, can alter the fate of the second echo from the bottom of the ice, says Bramson. Seismology, gravity and topography data could go a long way to revealing what lurks beneath the ice.
Whether anything could survive in such water is an open question. “We don’t know exactly what is in this water,” Orosei says.  “We don’t know the concentration of salts, which could be deadly to life.” But if life did evolve on Mars, he speculates, “these lakes could have been providing a Noah’s Ark that could have allowed life to survive even in in present conditions.“ More

Particles raining down from space offer 3-D views inside swirling tropical storms.

Muons created from cosmic rays that smash into Earth’s upper atmosphere have revealed the inner workings of cyclones over Japan, researchers report October 6 in Scientific Reports. The new imaging approach could lead to a better understanding of storms, the researchers say, and offer another tool to help meteorologists forecast the weather.

“Cosmic rays are sustainable natural resources that can be used everywhere on this planet for 24 hours [a day],” says geophysicist Hiroyuki Tanaka of the University of Tokyo, so it’s just a matter of taking advantage of them.

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Muons offer a glimpse inside storms because variations in air pressure and density change the number of particles that make it through a tempest. By counting how many muons arrived at a detector on the ground in Kagoshima, Japan as cyclones moved past, Tanaka and colleagues produced rough 3-D maps of the density of air inside the storms. The approach gave the team an inside look at the low-pressure regions at the centers rotating storm systems.

Muons, which are similar to electrons but roughly 200 times as massive, can scatter off molecules in the air. They’re also unstable, which means they break down into electrons and other particles called neutrinos given enough time. As air pressure increases, so does its density. That, in turn, increases the chances that a muon born from a cosmic ray will be bumped off its path on the way toward a detector or get slowed enough that it breaks down before it makes it all the way through the atmosphere.

For every 1 percent increase in air pressure, Tanaka and colleagues say, the number of muons that survive passage from the upper atmosphere to the ground decreases by about 2 percent.

Fewer muons make it through the high-pressure portions at the edges of a swirling cyclone (yellow and green in this muograph) than through the low-pressure regions in the center (red), providing a map of conditions inside the storm (illustrated outline). The darkened portion was outside the viewing angle of the muon detector.©2022 H.K.M. Tanaka

Tanaka has previously used muons from cosmic rays to look inside volcanoes, and he suspects that others have used the particles to study weather (SN: 4/22/22). But, he says, this appears to be the first time that anyone has made 3-D muon scans of the insides of a storm.

“It is an interesting approach,” says meteorologist Frank Marks of the National Oceanic and Atmospheric Administration’s Atlantic Oceanographic and Meteorological Laboratory in Miami, who wasn’t involved in the research.

He doesn’t expect muon imaging to replace conventional meteorological measurements, but it’s another tool that scientists could use. “[It] would be complementary to our existing techniques to provide 3-D mapping of the storms with our other traditional observing systems, like satellites and radar.” More

When NASA’s OSIRIS-REx arrived at near-Earth asteroid Bennu, scientists were dismayed to find a surface covered with hazardous-looking boulders.
But new research suggests that those boulders are surprisingly brittle. That’s potentially good news for the spacecraft, which is charged with grabbing a piece of Bennu on October 20 and returning it to Earth in 2023 (SN: 1/15/19). If the rocks are crumbly, that could lower the risk of damaging the spacecraft’s equipment.
That kind of rock also may be too fragile to survive the trip through Earth’s atmosphere without burning up. If so, scientists may be close to getting their hands on a never-before-seen kind of space rock, researchers report in a collection of papers published October 8 in Science and Science Advances.
Data taken from Earth before OSIRIS-REx launched suggested that Bennu’s surface would be sandy. So it was a shock to find a rough landscape strewn with boulders when the spacecraft arrived in 2018 (SN: 12/3/18).
“We had really convinced ourselves that Bennu was a smooth object,” says Daniella DellaGiustina, a planetary scientist at the University of Arizona in Tucson and member of the OSIRIS-REx team. “As everyone saw from the first pictures, that was not the case.”
The team found a relatively clear crater, nicknamed Nightingale, from which to retrieve a sample of the space rock (SN: 12/12/19). Still, the worry remains that the boulders might pose a safety hazard for the sampling system, which was designed to handle pebbles only a few centimeters across.
From late April through early June 2019, planetary scientist Ben Rozitis of the Open University in Milton Keynes, England, and colleagues mapped the way Bennu’s boulders retain heat, a clue to the rocks’ structure. Denser materials hold heat better than finer-grained ones, like how a sandy beach cools quickly after sundown, but single large rocks remain warm.
This map shows where carbon-bearing minerals (represented by redder colors) are located on Bennu’s surface. The opportunity to analyze those minerals could help scientists figure out how carbon got to the early Earth.A. Simon et al/Science 2020
Based on those maps — and maps of other surface properties, described in the series of papers released October 8 — Bennu’s boulders seem to come in two flavors: darker-colored rocks that are weaker and more porous and lighter-colored, denser rocks that are stronger and less porous. Even the denser rocks are much more porous and brittle than meteorites from similar asteroids that have been found on Earth. The least dense meteorites are about 15 percent porous; Bennu’s rocks seem to be between 30 and 50 percent porous, Rozitis and colleagues found.
“This is exciting,” says DellaGiustina, a coauthor of the new papers. The spacecraft and its instruments might “encounter some boulders at the sample site that might otherwise be difficult to ingest,” she says, but “if they’re porous and weak, then they might just break down,” making them easier to collect.
The lighter, denser rocks also appear to be shot through with veins of carbonate, which suggests that they were in the presence of flowing water at some point in their past (SN: 12/10/18). NASA chose Bennu as an asteroid to visit partly because it resembles carbonaceous chondrite meteorites, which scientists think are time capsules of the early solar system. Similar space rocks could have delivered water and organic materials to Earth billions of years ago.
But Bennu’s more porous rocks appear to be unlike anything in scientists’ current assortment of meteorites, Rozitis says. “This is one of the cool things about OSIRIS-REx — it’s quite likely it will pick up new material that isn’t in our meteorite collection,” he says.

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That’s believable, says meteor scientist Bill Cooke of NASA’s Marshall Space Flight Center in Huntsville, Ala. Observations of meteors have shown that low-density space rocks and dust burn up higher in Earth’s atmosphere than higher-density rocks.
“The old conventional wisdom was that the low-density stuff was from comets, and the high-density stuff was from asteroids,” he says. But recent observations show that some of the low-density rocks come from the orbits of asteroids. “So it is very plausible that low-density stuff from Bennu … would ablate higher in the atmosphere and not have a chance to create meteorites at all.”
If Bennu represents a missing piece in our understanding of the solar system’s history, studying that material in labs on Earth “will help us fill in an additional piece of the jigsaw,” Rozitis says. More

Bright, artificial lights are drowning out the night sky’s natural glow. Now, an exhibition is highlighting some of the consequences of a fading starry night — and how people can help restore it.

“Lights Out,” open through 2025 at the Smithsonian National Museum of Natural History in Washington, D.C., illuminates how light pollution is affecting astronomy, natural ecosystems and human cultures around the world. “We want people to understand that it’s a global problem, and it’s having broad impact,” says Jill Johnson, an exhibit developer at the museum.

Upon entering the exhibition, the dimly lit space resets the mood for nighttime exploration. The exhibition spans a long hallway that can be entered from either end. One entrance quickly draws in visitors with a personal connection. An interactive display invites you to experience your own night sky, whether in a city, suburb or remote location. Three tactile panels feature raised elements, including dots representing light pollution and crosses indicating visible stars. The more populated a place, the more dots are smattered across the panel.

Visitors can also listen to the artificial light and starlight in each sky through data that have been translated into sound. The multisensory experience is especially engaging for visitors who may not be able to experience the exhibition visually.

The other entrance offers a more didactic introduction to the exhibition. A timeline presents a brief history of human-made light, from fire-lit torches to today’s LEDs, and then segues to astronomy (SN: 1/19/23). Space scientists rely on light, both visible and not, to understand celestial bodies. And their views of the universe have become increasingly obstructed by artificial light.

“Astronomers were some of the first folks to sound the alarm on light pollution,” says Ryan Lavery, a public affairs specialist at the museum.

Astronomers aren’t the only scientists who have noticed the repercussions. Biologists have observed light pollution’s toll on plants and animals, whether harming corals’ moonlight-triggered reproduction or bats’ ability to pollinate flowers. Here, much of the evidence on display is visual. Photographs and specimens demonstrate the variety of critters that are active at night, while a glass case of preserved birds presents the grim consequences of light pollution. All of these birds died from striking buildings in Washington, D.C., or Baltimore after being disoriented by the bright cityscapes.

Losing dark, starry nights also affects human cultures. Another area of the exhibition presents people’s ancient and modern-day connections to the night sky through photographs, stories and cultural items. A glistening beadwork depicting the Milky Way was crafted specially for “Lights Out” by Gwich’in artist Margaret Nazon, who grew up staring at the stars in Canada’s Northwest Territories.

Our connections under a shared sky are emphasized in the exhibition’s small central theater. It replicates a starry night over Coudersport, Pa., through speckled lighting and walls bearing illustrations of trees and hills. A short film describes the star cluster Messier 45, also known as the Pleiades, and explains the stars’ origins according to tales from three cultures — the ancient Greeks, the Ainu in Japan and the Māori in New Zealand.

“Cultures all over the world have a deep relationship to the night sky,” says Stephen Loring, cocurator of the exhibition and an archaeologist at the museum. “If we lose the night sky, we lose an avenue to our understanding of what it is to be a human being.”

But the exhibition isn’t all bleak. Sprinkled throughout it are success stories of how people are reducing light pollution, from France’s outdoor lighting curfews to beach communities that have altered their lighting systems to avoid drawing hatchling sea turtles away from the ocean. And visitors may be heartened to learn about simple but meaningful actions that they can take, such as aiming outdoor lights downward and using the dimmest settings.

Overall, “Lights Out” instills a sense of hope and a desire to reconnect with the night sky. “This is an optimistic exhibition,” Loring says. “We can solve this problem.” More

On Mars, the speed of sound depends on its pitch.

All sound travels slower through Mars’ air compared with Earth’s. But the higher-pitched clacks of a laser zapping rocks travels slightly faster in the thin Martian atmosphere than the lower-pitched hum of the Ingenuity helicopter, researchers report April 1 in Nature.

These sound speed measurements from NASA’s Perseverance rover are part of a broader effort to monitor minute-by-minute changes in atmospheric pressure and temperature, like during wind gusts, on the Red Planet.

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“The wind is the sound of science for us,” says astrophysicist Baptiste Chide of Los Alamos National Laboratory in New Mexico.

To listen to the wind, Perseverance carries two microphones. One was meant to record audio during the mission’s complex entry, descent and landing, and while it didn’t work as hoped, it is now turned on occasionally to listen to the rover’s vitals (SN: 2/22/21; SN: 2/17/21). The other microphone is part of the rover’s SuperCam instrument, a mast-mounted mishmash of cameras and other sensors used to understand the properties of materials on the planet’s surface.

But these microphones also pick up other sounds, such as those made by the rover itself as its wheels crunch the surface, and by Perseverance’s flying companion, the robotic helicopter Ingenuity. The SuperCam instrument, for example, has a laser, which Perseverance fires at interesting rocks for further analysis (SN: 7/28/20). The microphone on SuperCam captures sounds from those laser shots, which helps researchers learn about the hardness of the target material, says planetary scientist Naomi Murdoch of the Institut Supérieur de l’Aéronautique et de l’Espace in Toulouse, France.

Murdoch, Chide and their colleagues listened to the laser’s clack-clack when zapping rocks. (“It doesn’t do, really, ‘pew pew,’” Murdoch says). When the laser hits a target, that blast creates a sound wave. Because scientists know when the laser fires and how far away a target is, they can measure the speed at which that sound wave travels through the air toward the SuperCam microphone.

The speed of this sound is about 250 meters per second, the team reports. That’s slower than on Earth, where sound travels through the air at about 340 m/s.

The slower speed isn’t surprising. What we hear as sound is actually pressure waves traveling through a medium like air, and the speed of those waves depends on the medium’s density and composition (SN: 10/9/20). Our planet’s atmosphere is 160 times as dense as the Martian atmosphere, and Earth’s air is mostly nitrogen and oxygen, whereas the Martian air is predominately carbon dioxide. So sound on Mars travels slower in that different air.

The team also used the SuperCam microphone to listen to the lower-pitch whirl of Ingenuity’s helicopter blades (SN: 12/10/21). From this lower-pitched sound, the researchers learned that there is a second speed of sound at the Martian surface at frequencies below 240 hertz, or slightly deeper than middle C on a piano: 240 m/s.

In contrast, at Earth’s surface, sound moves through the air at only one speed, no matter the pitch. The two speeds on Mars, the researchers say, are because of its carbon dioxide–rich atmosphere. Carbon dioxide molecules behave differently with one another when sound waves with frequencies above 240 hertz move through the air compared with those below 240 hertz, affecting the waves’ speed.

“We’ve proved that we can do science with a microphone on Mars,” Chide says. “We can do good science.”

The SuperCam microphone captures thousands of sound snippets per second. Those sounds are affected by air pressures, so the researchers can use that acoustic data to track detailed changes in air pressures over short timescales, and, in doing so, learn more about the Martian climate. While other Mars rovers have had wind, temperature and pressure sensors, those could sense changes only over longer periods.

“Listening to sounds on another planet is another way that helps all of us place ourselves as if we were there,” says Melissa Trainer, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., who was not part of this work.

The team is focusing on next collecting acoustic data at different times of day and different seasons on Mars.

“The pressure changes a lot on Mars throughout the year with the seasons,” Trainer says. “I’m really excited to see how the data might change as it gets collected through proceeding seasons.” More