Radiation-tolerant microbes might be able to live beneath Mars’ surface for hundreds of millions of years and may yet persist today, thanks in part — counterintuitively — to the Red Planet’s frigid, arid conditions.

In addition to being cold and dry, the Martian surface is constantly bombarded by cosmic rays, charged particles and other radiation from space. Previous studies have shown that desiccation vastly extends a microbe’s potential for surviving by limiting the production of highly reactive oxygen-bearing chemicals that can damage proteins and DNA, among other vital molecules within its tissues. To see how long microbes might survive such an onslaught on Mars, researchers desiccated five species of bacteria and one type of yeast, stored them at −80° Celsius and then irradiated them.  

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Some of the microbes might remain viable for only a few tens of thousands of years, experiments showed. But one species — Deinococcus radiodurans, a particularly radiation-hardy greebly that some scientists have nicknamed “Conan the bacterium” — might survive for as long as 280 million years if protected from radiation at soil depths of 10 meters or more, physical chemist Brian Hoffman and colleagues report online October 25 in Astrobiology.

D. radiodurans resists radiation damage by having multiple copies of chromosomes and other genetic material in each cell, as well as high levels of manganese-bearing antioxidants that help remove DNA-damaging chemicals (SN: 9/3/10). If similar microbes evolved on Mars, they too could persist for lengthy intervals, even possibly until now — which is “improbable but not impossible,” says Hoffman, of Northwestern University in Evanston, Ill.

Even if microbes that evolved on Mars ultimately succumbed to the harsh conditions, remnants of their proteins or other macromolecules may remain — offering hope that future missions, if equipped with the proper equipment, might be able to detect those signs of former life.     More

Maybe hold off on that Martian ice fishing trip. Two new studies splash cold water on the idea that potentially habitable lakes of liquid water exist deep under the Red Planet’s southern polar ice cap.

The possibility of a lake roughly 20 kilometers across was first raised in 2018, when the European Space Agency’s Mars Express spacecraft probed the planet’s southern polar cap with its Mars Advanced Radar for Subsurface and Ionosphere Sounding, or MARSIS, instrument. The orbiter detected bright spots on radar measurements, hinting at a large body of liquid water beneath 1.5 kilometers of solid ice that could be an abode to living organisms (SN: 7/25/18). Subsequent work found hints of additional pools surrounding the main lake basin (SN: 9/28/20).

But the planetary science community has always held some skepticism over the lakes’ existence, which would require some kind of continuous geothermal heating to maintain subglacial conditions (SN: 2/19/19). Below the ice, temperatures average –68° Celsius, far past the freezing point of water, even if the lakes are a brine containing a healthy amount of salt, which lowers water’s freezing point. An underground magma pool would be needed to keep the area liquid — an unlikely scenario given Mars’ lack of present-day volcanism.

“If it’s not liquid water, is there something else that could explain the bright radar reflections we’re seeing?” asks planetary scientist Carver Bierson of Arizona State University in Tempe.

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In a study published in the July 16 Geophysical Research Letters, Bierson and colleagues describe a couple other substances that could explain the reflections. Radar’s reflectivity depends on the electrical conductivity of the material the radar signal moves through. Liquid water has a fairly distinctive radar signature, but examining the electrical properties of both clay minerals and frozen brine revealed those materials could mimic this signal.

Adding weight to the non-lake explanation is a study from an independent team, published in the same issue of Geophysical Research Letters. The initial 2018 watery findings were based on MARSIS data focused on a small section of the southern ice cap, but the instrument has now built up three-dimensional maps of the entire south pole, where hundreds to thousands of additional bright spots appear.

“We find them literally all over the region,” says planetary scientist Aditya Khuller, also of Arizona State University. “These signatures aren’t unique. We see them in places where we expect it to be really cold.”

Creating plausible scenarios to maintain liquid water in all of these locations would be a tough exercise. Both Khuller and Bierson think it is far more likely that MARSIS is pointing to some kind of widespread geophysical process that created minerals or frozen brines.

While previous work had already raised doubts about the lake interpretation, these additional data points might represent the pools’ death knell. “Putting these two papers together with the other existing literature, I would say this puts us at 85 percent confidence that this is not a lake,” says Edgard Rivera-Valentín, a planetary scientist at the Lunar and Planetary Institute in Houston who was not involved in either study.

The lakes, if they do exist, would likely be extremely cold and contain as much as 50 percent salt — conditions in which no known organisms on Earth can survive. Given that, the pools wouldn’t make particularly strong astrobiological targets anyway, Rivera-Valentín says. (SN: 5/11/20).

Lab work exploring how substances react to conditions at Mars’ southern polar ice cap could help further constrain what generates the bright radar spots, Bierson says.

In the meantime, Khuller already has his eye on other areas of potential habitability on the Red Planet, such as warmer midlatitude regions where satellites have seen evidence of ice melting in the sun. “I think there are places where liquid water could be on Mars today,” he says. “But I don’t think it’s at the south pole.”  More

Neptune’s atmospheric temperature is on an unexpected roller-coaster ride, and it could take decades for scientists to piece together what’s happening at the distant planet.

The ice giant’s global temperature dropped about 8 degrees Celsius between 2003 and 2012 at the start of Neptune’s summer, researchers report April 11 in Planetary Sciences Journal. Then from 2018 to 2020, thermal images show that the planet’s south pole brightened dramatically, indicating a spike of 11 degrees C (SN: 10/2/07).

Naomi Rowe-Gurney, a planetary scientist at NASA Goddard Space Flight Center in Greenbelt, Md., and colleagues looked at 17 years of mid-infrared data from ground-based telescopes and the no-longer-functioning Spitzer Space Telescope (SN: 7/18/18; SN: 1/28/20). The researchers used infrared light to pierce Neptune’s top cloud layer and peer at its stratosphere, where the planet’s atmospheric chemistry comes into view.

Each Neptune year lasts 165 Earth years, so the time period analyzed — from 2003 to 2020 — is essentially equivalent to five weeks on Earth. The wildest temperature shift occurred from 2018 to 2020, when the atmospheric temperature at Neptune’s south pole rose from –121° C to –110° C.

“We weren’t expecting any seasonal changes to happen in this short time period, because we’re not even seeing a full season,” says Rowe-Gurney. “It’s all very strange and interesting.”

The researchers don’t yet know what’s causing the temperature changes. The sun’s ultraviolet rays break up methane molecules in the stratosphere, so that chemistry or even the sun’s activity cycle could be a trigger. Nailing down specifics requires more observations. “We need to keep observing over the next 20 years to see a full season and see if something else changes,” says Rowe-Gurney.

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Scientists have coaxed one of the universe’s most stubborn elements into a new compound.

Formed under intense pressures, the newly discovered compound packs helium atoms into crystalline iron, researchers report February 25 in Physical Review Letters. The compound joins a short list of materials that incorporate the normally unreactive element and suggests that helium from the early solar system could be stored in the iron that makes up Earth’s core.

Helium is one of the least reactive elements on the periodic table. Like the other noble gases, helium doesn’t gain or lose electrons easily and so does not normally form chemical compounds. But under extremely high pressures, helium can interact with a few other elements, including nitrogen and sodium — and now iron, research shows.

An iron-helium compound, shown here in artificial color using a technique called secondary ion mass spectrometry, forms under high temperature and pressure. Blue and black areas mark the background, while the orange and red area represents the sample. ©2025 Hirose et al. CC-BY-ND

To make the new iron compound, physicist Kei Hirose of the University of Tokyo and his colleagues squeezed iron and helium together in a diamond anvil cell, a high-pressure device that subjected the elements to pressures greater than 50,000 Earth atmospheres and temperatures above 1,000 degrees Celsius. This compression formed crystals containing both iron and helium.

The volume of the crystal formed was larger than that of a crystal of pure iron at the same pressure, the team found. The researchers attributed this increase to helium ions packing into interstitial sites, the tiny spaces between iron atoms in the crystal. But the helium atoms don’t bond directly to iron — they’re too unreactive, even at extreme conditions. More

Astronomers have spotted a bright gamma-ray burst that upends previous theories of how these energetic cosmic eruptions occur.

For decades, astronomers thought that GRBs came in two flavors, long and short — that is, lasting longer than two seconds or winking out more quickly. Each type has been linked to different cosmic events. But about a year ago, two NASA space telescopes caught a short GRB in long GRB’s clothing: It lasted a long time but originated from a short GRB source.

“We had this black-and-white vision of the universe,” says astrophysicist Eleonora Troja of the Tor Vergata University of Rome. “This is the red flag that tells us, nope, it’s not. Surprise!”

This burst, called GRB 211211A, is the first that unambiguously breaks the binary, Troja and others report December 7 in five papers in Nature and Nature Astronomy.

Prior to the discovery of this burst, astronomers mostly thought that there were just two ways to produce a GRB. The collapse of a massive star just before it explodes in a supernova could make a long gamma-ray burst, lasting more than two seconds (SN: 10/28/22). Or a pair of dense stellar corpses called neutron stars could collide, merge and form a new black hole, releasing a short gamma-ray burst of two seconds or less.

But there had been some outliers. A surprisingly short GRB in 2020 seemed to come from a massive star’s implosion (SN: 8/2/21). And some long-duration GRBs dating back to 2006 lacked a supernova after the fact, raising questions about their origins.

“We always knew there was an overlap,” says astrophysicist Chryssa Kouveliotou of George Washington University in Washington, D.C., who wrote the 1993 paper that introduced the two GRB categories, but was not involved in the new work. “There were some outliers which we did not know how to interpret.”

There’s no such mystery about GRB 211211A: The burst lasted more than 50 seconds and was clearly accompanied by a kilonova, the characteristic glow of new elements being forged after a neutron star smashup.

This shows the glow of a kilonova that followed the oddball gamma-ray burst called GRB 211211A, in images from the Gemini North telescope and the Hubble Space Telescope.M. Zamani/International Gemini Observatory/NOIRLab/NSF/AURA, NASA, ESA

“Although we suspected it was possible that extended emission GRBs were mergers … this is the first confirmation,” says astrophysicist Benjamin Gompertz of the University of Birmingham in England, who describes observations of the burst in Nature Astronomy. “It has the kilonova, which is the smoking gun.”

NASA’s Swift and Fermi space telescopes detected the explosion on December 11, 2021, in a galaxy about 1.1 billion light-years away. “We thought it was a run-of-the-mill long gamma-ray burst,” says astrophysicist Wen-fai Fong of Northwestern University in Evanston, Ill.

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It was relatively close by, as GRBs go. So that allowed Fong’s and Troja’s research groups to independently continue closely observing the burst in great detail using telescopes on the ground, the teams report in Nature.

As the weeks wore on and no supernova appeared, the researchers grew confused. Their observations revealed that whatever had made the GRB had also emitted much more optical and infrared light than is typical for the source of a long GRB.

After ruling out other explanations, Troja and colleagues compared the burst’s aftereffects with the first kilonova ever observed in concert with ripples in spacetime called gravitational waves (SN: 10/16/17). The match was nearly perfect. “That’s when many people got convinced we were talking about a kilonova,” she says.

In retrospect, it feels obvious that it was a kilonova, Troja says. But in the moment, it felt as impossible as seeing a lion in the Arctic. “It looks like a lion, it roars like a lion, but it shouldn’t be here, so it cannot be,” she says. “That’s exactly what we felt.”

Now the question is, what happened? Typically, merging neutron stars collapse into a black hole almost immediately. The gamma rays come from material that is superheated as it falls into the black hole, but the material is scant, and the black hole gobbles it up within two seconds. So how did GRB 211211A keep its light going for almost a minute?

It’s possible that the neutron stars first merged into a single, larger neutron star, which briefly resisted the pressure to collapse into a black hole. That has implications for the fundamental physics that describes how difficult it is to crush neutrons into a black hole, Gompertz says.

Another possibility is that a neutron star collided with a small black hole, about five times the mass of the sun, instead of another neutron star. And the process of the black hole eating the neutron star took longer.

Or it could have been something else entirely: a neutron star merging with a white dwarf, astrophysicist Bing Zhang of the University of Nevada, Las Vegas and colleagues suggest in Nature. “We suggest a third type of progenitor, something very different from the previous two types,” he says.

White dwarfs are the remnants of smaller stars like the sun, and are not as dense or compact as neutron stars. A collision between a white dwarf and a neutron star could still produce a kilonova if the white dwarf is very heavy.

The resulting object could be a highly magnetized neutron star called a magnetar (SN: 12/1/20). The magnetar could have continued pumping energy into gamma rays and other wavelengths of light, extending the life of the burst, Zhang says.

Whatever its origins, GRB 211211A is a big deal for physics. “It is important because we wanted to understand, what on Earth are these events?” Kouveliotou says.

Figuring out what caused it could illuminate how heavy elements in the universe form. And some previously seen long GRBs that scientists thought were from supernovas might actually be actually from mergers.

To learn more, scientists need to find more of these binary-busting GRBs, plus observations of gravitational waves at the same time. Trejo thinks they’ll be able to get that when the Laser Interferometer Gravitational-Wave Observatory, or LIGO, comes back online in 2023.

“I hope that LIGO will produce some evidence,” Kouveliotou says. “Nature might be graceful and give us a couple of these events with gravitational wave counterparts, and maybe [help us] understand what’s going on.” More