Eliana Willis

Jupiter’s icy moon Europa could give the word “moonlight” a whole new meaning. New lab experiments suggest the nightside of this moon glows in the dark.
Europa’s surface, thought to be mostly water ice laced with various salts, is continually bombarded with energetic electrons by Jupiter’s intense magnetic field (SN: 5/19/15). When researchers simulated that interaction in the lab by shooting electrons at salty ice samples, the ice glowed. The brightness of that glow depended on the kind of salt in the ice, researchers report online November 9 in Nature Astronomy.
If the same interaction on Europa creates this never-before-seen kind of moonlight, a future mission there, such as NASA’s planned Europa Clipper spacecraft, may be able to use this ice glow map Europa’s surface composition. That, in turn, could give insight into the salinity of the ocean thought to lurk under Europa’s icy crust (SN: 6/14/19).
“That has implications for the temperature of that liquid water — the freezing point; it has implications for the thickness of the ice shell; it has implications for the habitability of that liquid water,” says Jennifer Hanley, a planetary scientist at Lowell Observatory in Flagstaff, Ariz. not involved in the new work. Europa’s subsurface ocean is considered one of the most promising places to look for extraterrestrial life in the solar system (SN: 4/8/20).

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The discovery of Europa’s potential ice glow “was serendipity,” says Murthy Gudipati, who studies the physics and chemistry of ices at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Gudipati and colleagues originally set out to investigate how electron bombardment might change the chemistry of Europa’s surface ice. But in video footage of their initial experiments, the team noticed that ice samples pelted with electrons gave off an unexpected glow.
Intrigued, the researchers turned their electron beam on samples of pure water ice, as well as water ice mixed with different salts. Each ice core was cooled to the surface temperature of Europa (about –173° Celsius) and showered with electrons that had the same energies as those that strike Europa. Over 20 seconds of irradiation, a spectrometer measured the wavelengths of light, or spectrum, given off by the ice.
The ice samples all gave off a whitish glow, because they emitted light at many different wavelengths. But the brightness of each ice sample depended on its composition. Ice containing sodium chloride, also known as table salt, or sodium carbonate appeared dimmer than pure water ice. Ice mixed with magnesium sulfate, on the other hand, was brighter.

“I was doing some back of the envelope calculations [of] what would be the brightness of Europa, if we were to be standing on it in the dark,” Gudipati says. “It’s approximately … as bright as me walking on the beach in full moonlight.”
Based on the specs proposed for a camera to fly on the Europa Clipper mission, Gudipati and colleagues estimate that the spacecraft could see Europa’s ice glow during a flyby of the dark side of the moon. Dark patches of Europa could reveal sodium-rich regions, while brighter areas may be rich in magnesium.
But seeing ice glow in the lab does not necessarily mean it happens the same way on Europa, Hanley cautions. Jupiter’s icy moon has been barraged by high-energy electrons for a lot longer than 20 seconds. “Is there ever a point where you might break down the salts, and this glow stops happening?” she wonders.
Other planetary scientists, meanwhile, are not convinced that Europa’s surface is highly salted. These researchers, including Roger Clark of the Planetary Science Institute in Lakewood, Colo., think the apparent hints of salts on Europa are actually created by acids, such as sulfuric acid. Europa’s surface may be coated in both salts and acids, Clark says. “What [the researchers] need to do next is irradiate acids … to see if they can tell the difference between salt with water ice and acids with water ice.” More

Jupiter may be the first planet besides Earth known to host atmospheric light shows called “sprites” or “elves.”
Sprites (SN: 6/14/02) and elves (SN: 12/23/95) are two kinds of atmospheric glows that form when lightning alters the electromagnetic environment in the atmosphere above a storm. On Earth, these electromagnetic upsets cause nitrogen molecules in the upper atmosphere to emit a brief, reddish glow. Sprites can brighten a region of the sky tens of kilometers across, while elves can span hundreds of kilometers (SN: 12/21/96).
Scientists suspected these atmospheric phenomena might appear on other planets that crackle with lightning (SN: 6/19/18). But until now, no one had seen hints of sprites or elves on another world.
From 2016 to 2020, the ultraviolet spectrograph on NASA’s Juno spacecraft, in orbit around Jupiter, caught 11 superfast flashes of light across the giant planet. Those flares, reported online October 27 in the Journal of Geophysical Research: Planets, lasted an average 1.4 milliseconds, which is about as fleeting as sprites and elves on Earth. The ultraviolet light was at wavelengths emitted by molecular hydrogen — the type of glow expected of sprites or elves on Jupiter, whose atmosphere is made mostly of hydrogen, rather than nitrogen.
Juno would need to spot a lightning strike at the same place as one of these bright flares to confirm that they actually are sprites or elves, says study coauthor Rohini Giles, a planetary scientist at the Southwest Research Institute in San Antonio, Texas. “But there is reasonably good circumstantial evidence,” she says. The flashes originated a few hundred kilometers above Jupiter’s layer of water clouds, where lightning typically forms, and several appeared in known stormy regions.
Observations of these events when Juno is closer to Jupiter may reveal their size, and help determine whether it is sprites or elves (or both) lighting up Jupiter’s atmosphere. More

Past observations have suggested that there’s water on the moon. New telescope observations conclude that those findings hold water.
Spacecraft have seen evidence of water ice in permanently shadowed craters at the lunar poles (SN: 5/9/16), as well as hints of water molecules on the sunlit surface (SN: 9/23/09). But water sightings in sunlit regions have relied on detection of infrared light at a wavelength that could also be emitted by other hydroxyl compounds, which contain hydrogen and oxygen. 
Now, the Stratospheric Observatory for Infrared Astronomy, or SOFIA, has detected an infrared signal unique to water near the lunar south pole, researchers report online October 26 in Nature Astronomy. “This is the first unambiguous detection of molecular water on the sunlit moon,” says study coauthor Casey Honniball, a lunar scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “This shows that water is not just in the permanently shadowed regions — that there are other places on the moon that we could potentially find it.”
These observations could inform future missions to the moon that will scout out lunar water as a potential resource for human visitors (SN: 12/16/19).

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SOFIA, operated by NASA and the German Aerospace Center, is a 2.5-meter telescope that rides aboard a jumbo jet to get clear views of the sky (SN: 2/17/16). During a flight in August 2018, the telescope detected 6-micrometer infrared light emanating from a region near the moon’s southern Clavius crater. This wavelength of light is generated by the vibrations of sunlight-heated water molecules, but not other compounds containing hydroxyl, which consists of an oxygen atom bound to a hydrogen atom.
“I thought it was really brilliant” to confirm the presence of water on the moon with observations at this wavelength, says Jessica Sunshine, a planetary scientist at the University of Maryland in College Park. Sunshine was involved in past observations that spotted hints of water on the moon, but was not involved in the new study.
Based on the brightness of the observed infrared light, Honniball’s team calculated a water concentration of about 100 to 400 parts per million around the Clavius crater. That’s less than half a liter of water per metric ton of lunar soil. This concentration was about what the researchers expected, based on past spacecraft observations.
These water molecules are not frozen in ice, like the water in permanently shadowed regions of the moon. Nor is it liquid, Sunshine says. “There’s no moon puddles.” Instead, the water molecules are thought to be bound inside some other material on the lunar surface.
“The only way for us to be seeing water on the [sunlit] moon is if it is sheltered from this harsh environment,” Honniball says. These water molecules could be encased in glass forged by micrometeorite impacts, or wedged between soil grains that shield the water from blistering solar radiation.
Water could have formed on the moon itself, from hydrogen ions in the continual outward flow of charged particles from the sun reacting with oxygen on the surface (SN: 10/6/14). Or, if the water is stored in impact glass, it could have been delivered to the moon by micrometeorites. More

NASA’s OSIRIS-REx spacecraft is a cosmic rock collector. Cheers erupted from mission control at 6:12 p.m. EDT on October 20 as scientists on Earth got word that the spacecraft had gently nudged a near-Earth asteroid called Bennu, and grabbed some of its rocks to return to Earth.
“The spacecraft did everything it was supposed to do,” said mission principal investigator Dante Lauretta of the University of Arizona in Tucson on a NASA TV webcast. “I can’t believe we actually pulled this off.”
OSIRIS-REx arrived at Bennu in December 2018, and spent almost two years making detailed maps of the 500-meter-wide asteroid’s surface features and composition (SN: 10/8/20). Observations from Earth suggested Bennu should be smooth and sandy, but when OSIRIS-REx arrived, it found a treacherous, rocky landscape.
The team selected a relatively smooth patch in a crater named Nightingale. The spot was not without hazards, though — the team was so worried about a particularly large rock nearby that they named it “Mount Doom” (SN: 12/12/19).

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Luckily, the spacecraft did not need to fully land in the crater to complete its mission. As it hovered just above the surface, OSIRIS-REx reached out a robotic arm with an instrument called TAGSAM at the end, for Touch-And-Go Sample Acquisition Mechanism. The instrument tapped the asteroid lightly for several seconds, and released a burst of nitrogen gas to disturb the surface dust and pebbles. Once those small rocks were lofted, some hopefully were blown into the sample collector.
Because signals from Earth took 18½ minutes to reach Bennu, the spacecraft performed the sampling sequence autonomously. When the mission team got the signal that the spacecraft had finished its job and retreated to a safe distance from Bennu, team members pumped their arms in the air, cheered and sent each other socially distant high-fives and hugs.
OSIRIS-REx is not the first spacecraft to grab samples from an asteroid. That distinction goes to Japan’s Hayabusa mission, which brought back grains of asteroid Itokawa in 2010 (SN: 6/14/10). An encore to that mission, Hayabusa2, collected samples of asteroid Ryugu last year, and is on track to land in Australia in December (SN: 2/22/19).
But OSIRIS-REx attempted to collect much more material than Hayabusa2 did. Hayabusa2 hoped to collect 100 milligrams; OSIRIS-REx is aiming for a minimum of 60 grams, or a little more than two ounces.
Hayabusa2’s scientists have no way to know how much material it actually collected until the spacecraft returns to Earth. But OSIRIS-REx’s team plans to find out using the spacecraft itself. On October 24, the spacecraft will extend its arm and spin its whole body. The difference in the way it spins before and after the sample collection will reveal the mass of the sample.
OSIRIS-REx will return to Earth in 2023, where scientists will analyze the rocks in hopes of unlocking details of the history of the solar system and the origins of water and life on Earth (SN: 1/15/19). More

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

A two-month stint on the moon would expose astronauts to roughly the same amount of radiation as they would get living on the International Space Station for five months, according to new measurements from the lunar surface.
Detectors on China’s lunar lander Chang’e-4 measured radiation from galactic cosmic rays at the moon’s surface in 2019, from January 3 to 12 — just after landing on the farside of the moon — and again from January 31 to February 10. An astronaut would be exposed to an average daily dose of 1,369 microsieverts of radiation, researchers report online September 25 in Science Advances.
That’s about 2.6 times as high as the average daily radiation exposure of 523 microsieverts recorded inside the ISS, the scientists say. Being on the moon “for two months would be OK. That is about the same amount of radiation astronauts receive at the ISS [over five months] and wouldn’t be incredibly dangerous,” says coauthor Robert Wimmer-Schweingruber, a physicist at Christian Albrechts University in Kiel, Germany.
The new study is perhaps the first to measure cosmic radiation at the moon’s surface, says Jeffery Chancellor, a physicist at Louisiana State University in Baton Rouge. “This is [a] pretty cool bit of data.” He cautions that radiation levels on other parts of the space station could be higher, so the authors may have overprojected the exposure difference between the moon’s surface and the ISS.
Galactic cosmic rays, high-energy charged particles that zip through space, come from outside the solar system. Earth’s magnetic field protects humans from these rays, but in space, it’s a whole different story.
Long exposure to such radiation can cause cellular and DNA damage resulting in cancers, cataracts, cardiac problems, neurodegenerative diseases and behavioral impairments, animal studies have shown (SN: 7/15/20). So far, it’s unclear exactly what impact such exposure might have on human health. The effects of spending a large amount of time in space may show many years after someone has been exposed, says Marjan Boerma, a radiation biologist at the University of Arkansas for Medical Sciences in Little Rock. 
The findings come at a time when United States and other nations are making plans to land humans on moon for the first time in decades (SN: 12/16/19). NASA has announced its plans to land the first U.S. woman and a man on the moon’s surface by 2024. More