Eliana Willis

Samples of the asteroid Ryugu are the most pristine pieces of the solar system that scientists have in their possession.

A new analysis of Ryugu material confirms the porous rubble-pile asteroid is rich in carbon and finds it is extraordinarily primitive (SN: 3/16/20). It is also a member of a rare class of space rocks known as CI-type, researchers report online June 9 in Science. 

Their analysis looked at material from the Japanese mission Hayabusa2, which collected 5.4 grams of dust and small rocks from multiple locations on the surface of Ryugu and brought that material to Earth in December 2020 (SN: 7/11/19; SN: 12/7/20). Using 95 milligrams of the asteroid’s debris, the researchers measured dozens of chemical elements in the sample and then compared abundances of several of those elements to those measured in rare meteorites classified as CI-type chondrites. Fewer than 10 meteorites found on Earth are CI chondrites.

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This comparison confirmed Ryugu is a CI-type chondrite. But it also showed that unlike Ryugu, the meteorites appear to have been altered, or contaminated, by Earth’s atmosphere or even human handling over time. “The Ryugu sample is a much more fresh sample,” says Hisayoshi Yurimoto, a geochemist at Hokkaido University in Sapporo, Japan.

The researchers also measured the abundances of manganese-53 and chromium-53 in the asteroid and determined that melted water ice reacted with most of the minerals around 5 million years after the solar system’s start, altering those minerals, says Yurimoto. That water has since evaporated, but those altered minerals are still present in the samples. By studying them, the researchers can learn more about the asteroid’s history.   More

Four billion years ago, lava spilled onto the moon’s crust, etching the man in the moon we see today. But the volcanoes may have also left a much colder legacy: ice.

Two billion years of volcanic eruptions on the moon may have led to the creation of many short-lived atmospheres, which contained water vapor, a new study suggests. That vapor could have been transported through the atmosphere before settling as ice at the poles, researchers report in the May Planetary Science Journal.

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Since the existence of lunar ice was confirmed in 2009, scientists have debated the possible origins of water on the moon, which include asteroids, comets or electrically charged atoms carried by the solar wind (SN: 11/13/09). Or, possibly, the water originated on the moon itself, as vapor belched by the rash of volcanic eruptions from 4 billion to 2 billion years ago.

“It’s a really interesting question how those volatiles [such as water] got there,” says Andrew Wilcoski, a planetary scientist at the University of Colorado Boulder. “We still don’t really have a good handle on how much are there and where exactly they are.”

Wilcoski and his colleagues decided to start by tackling volcanism’s viability as a lunar ice source. During the heyday of lunar volcanism, eruptions happened about once every 22,000 years. Assuming that H2O constituted about a third of volcano-spit gasses — based on samples of ancient lunar magma — the researchers calculate that the eruptions released upward of 20 quadrillion kilograms of water vapor in total, or the volume of approximately 25 Lake Superiors.

Some of this vapor would have been lost to space, as sunlight broke down water molecules or the solar wind blew the molecules off the moon. But at the frigid poles, some could have stuck to the surface as ice.

For that to happen, though, the rate at which the water vapor condensed into ice would have needed to surpass the rate at which the vapor escaped the moon. The team used a computer simulation to calculate and compare these rates. The simulation accounted for factors such as surface temperature, gas pressure and the loss of some vapor to mere frost.

About 40 percent of the total erupted water vapor could have accumulated as ice, with most of that ice at the poles, the team found. Over billions of years, some of that ice would have converted back to vapor and escaped to space. The team’s simulation predicts the amount and distribution of ice that remains. And it’s no small amount: Deposits could reach hundreds of meters at their thickest point, with the south pole being about twice as icy as the north pole.

The results align with a long-standing assumption that ice dominates at the poles because it gets stuck in cold traps that are so cold that ice will stay frozen for billions of years.

“There are some places at the lunar poles that are as cold as Pluto,” says planetary scientist Margaret Landis of the University of Colorado Boulder.

Volcanically sourced water vapor traveling to the poles, though, probably depends on the presence of an atmosphere, say Landis, Wilcoski and their colleague Paul Hayne, also a planetary scientist at the University of Colorado Boulder. An atmospheric transit system would have allowed water molecules to travel around the moon while also making it more difficult for them to flee into space. Each eruption triggered a new atmosphere, the new calculations indicate, which then lingered for about 2,500 years before disappearing until the next eruption some 20,000 years later.

This part of the story is most captivating to Parvathy Prem, a planetary scientist at Johns Hopkins Applied Physics Laboratory in Laurel, Md., who wasn’t involved in the research. “It’s a really interesting act of imagination.… How do you create atmospheres from scratch? And why do they sometimes go away?” she says. “The polar ices are one way to find out.”

If lunar ice was belched out of volcanoes as water vapor, the ice may retain a memory of that long-ago time. Sulfur in the polar ice, for example, would indicate that it came from a volcano as opposed to, say, an asteroid. Future moon missions plan to drill for ice cores that could confirm the ice’s origin.

Looking for sulfur will be important when thinking about lunar resources. These water reserves could someday be harvested by astronauts for water or rocket fuel, the researchers say. But if all the lunar water is contaminated with sulfur, Landis says, “that’s a pretty critical thing to know if you plan on bringing a straw with you to the moon.” More

Any Martians out there should learn to duck and cover.

On May 4, the Red Planet was rocked by a roughly magnitude 5 temblor, the largest Marsquake detected to date, NASA’s Jet Propulsion Laboratory in Pasadena, Calif., reports. The shaking lasted for more than six hours and released more than 10 times the energy of the previous record-holding quake.

The U.S. space agency’s InSight lander, which has been studying Mars’ deep interior since touching down on the planet in 2018 (SN: 11/26/18), recorded the event. The quake probably originated near the Cerberus Fossae region, which is more than 1,000 kilometers from the lander.

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Cerberus Fossae is known for its fractured surface and frequent rockfalls. It makes sense that the ground would be shifting there, says geophysicist Philippe Lognonné, principal investigator of the Seismic Experiment for Interior Structure, InSight’s seismometer. “It’s an ancient volcanic bulge.”

Just like earthquakes reveal information about our planet’s interior structure, Marsquakes can be used to probe what lies beneath Mars’ surface (SN: 7/22/21). And a lot can be learned from studying this whopper of a quake, says Lognonné, of the Institut de Physique du Globe de Paris. “The signal is so good, we’ll be able to work on the details.” More

On Jupiter’s moon Io, lava creeping beneath frost may give rise to fields of towering dunes.

That finding, described April 19 in Nature Communications, suggests that dunes may be more common on other worlds than previously thought, though the lumps may form in odd ways.  

“In some sense, these [other worlds] are looking more familiar,” says George McDonald, a planetary scientist at Rutgers University in Piscataway, N.J. “But the more you think about it, they feel more and more exotic.”

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Io is a world crowded with erupting volcanoes, created when the gravitational forces of Jupiter and some of its other moons pull on Io and generate heat (SN: 8/6/14). Around 20 years ago, scientists reported another type of feature on Io’s dynamic surface — hummocky ridges. The features resemble dunes, but that couldn’t be the case, scientists reasoned, because Io’s atmosphere is too thin for winds to whip up a dunescape.

But in recent years, dunelike features have been discovered on comet 67P (SN: 9/21/20) and Pluto (SN: 8/24/21), planetary bodies that also lack thick atmospheres. Inspired by those alien dunescapes, McDonald and his colleagues revisited the matter of Io’s mysterious lumps. All they needed was some type of airborne force to sculpt the moon’s dunes.

On Earth, powerful explosions of steam occur when flows of molten rock encounter bodies of water. While water isn’t found on Io, sulfur dioxide frost is pervasive. So the scientists hypothesize that when lava slowly flows into and just under a frost layer, jets of sulfur dioxide gas could burst from the frost. Those jets could send grains of rock and other material flying and forming dunes.

The researchers calculate that an advancing lava flow, buried under at least 10 centimeters of frost, could sublimate some of the frost into pockets of hot vapor. When enough vapor accumulates and the pressure becomes high enough to match or overcome the weight of the overlying frost, the vapor could burst out at velocities over 70 kilometers per hour. These bursts could propel grains with diameters from 20 micrometers to 1 centimeter in size, the team estimates.  

Analyzing images of Io’s surface, collected by NASA’s now-defunct Galileo probe, revealed highly reflective streaks of material radiating outward over dunes in front of lava flows — possibly material newly deposited at the time by vapor jets.

This image, taken by NASA’s now-defunct Galileo spacecraft, shows dunelike lumps on Jupiter’s third-largest moon Io. The dark area (lower left) is a lava flow, and the bright streaks that radiate outward may be evidence of material strewn by jets of vapor that burst from frost heated by the lava.JPL-Caltech/NASA, Rutgers Univ.

What’s more, using the images to measure the hummocky features showed that their dimensions align with those of dunes on other planetary bodies. Some of the Ionian dunes are over 30 meters high, the team estimates.

“I think a lot of [scientists] looked at those and thought, hey, these really could be dunes,” says Jani Radebaugh, a planetary scientist at Brigham Young University in Provo, Utah, who was not involved in the study. “But what’s exciting about it is that they’ve come up with a good physical mechanism to explain how it’s possible.”

Io is typically thought of as a world of volcanoes. The possibility of dunes suggests that there might be more going on there than scientists thought, McDonald says. “It certainly adds a layer of complexity.” More

The continuing search for life beyond Earth is driving many of the priorities for what’s next when it comes to U.S. planetary exploration. In a new report that could shape the next 10 years of planetary missions, Mars, Uranus and Saturn’s moon Enceladus have come out on top.

This report is the latest decadal survey for planetary science and astrobiology. Every 10 years, experts convened by the National Academies of Sciences, Engineering and Medicine compile a look at the state of the field and pull together a list of recommended priorities for the next decade of exploration. The new survey, which covers 2023 to 2032, will be used by NASA, the National Science Foundation and others to help guide which projects are pursued and funded.

The survey is meant in part “to identify the key scientific questions that are the most important” to pursue in the next decade and assess how best to answer them, astrophysicist Robin Canup said April 19 during a news conference after the report was released. Canup, of the Southwest Research Institute in Boulder, Colo., is a cochair of the steering committee for the decadal survey.

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At the top of the list, the report recommends continuing the Mars sample-return effort by developing a mission that will retrieve, as soon as possible, the rock and soil samples that NASA’s Perseverance rover is collecting and storing (SN: 9/10/21). This multipart sample-return mission was also the top priority of the previous decadal survey, released in 2011 (SN: 3/7/11). Those samples could hold hints of past signs of life on the Red Planet.

The report also suggests that the next Mars mission, after the sample-return one, should look for signs of life in the ice as well as gaseous biosignatures in the atmosphere. That one is farther down the priority list, though.

Next in the line after the Mars sample-return mission is a large, several-billion-dollar mission to send an orbiter and probe to Uranus to explore the planet, its ring system and its moons. Uranus and the solar system’s other ice giant, Neptune, were visited once, in the late 1980s, when Voyager 2 flew by each.

The time has come to go back, scientists say (SN: 2/10/16). “I’m really thrilled to see that they picked a mission to go back and follow up on those incredible discoveries and those wonderful images that Voyager took,” says planetary scientist Linda Spilker of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., who was not involved in the decadal survey. Spilker began her career with Voyager.

What’s more, better understanding the ice giants in our solar system could help scientists decipher the mysteries of faraway worlds. In the hunt for planets outside our solar system, the most common type of known exoplanets are those like Neptune and Uranus.

A mission to Uranus “will be transformative,” says planetary scientist Amy Simon of NASA Goddard Space Flight Center in Greenbelt, Md., and a member of the decadal steering committee. “We’re sure there’s going to be fantastic discoveries.”  

This mission could launch in June 2031 or April 2032, the report suggests. After swinging by Jupiter to use the giant planet’s gravity to fling it faster, the spacecraft would arrive at Uranus 13 years after its launch. Once there, the orbiter would drop a probe in the atmosphere, sampling its composition as never before.

The next highest priority is sending an “orbilander” to Saturn’s moon Enceladus, a world known to have easily accessible liquid water (SN: 5/2/06). NASA’s now-defunct Cassini mission discovered in 2005 that this small moon spews geysers of water into space, and more recent research suggests that water coming from subsurface locales has salts, possibly indicating warm pockets of water interacting with rock — and brewing an environment that may host life (SN: 8/4/14).

Does Enceladus (shown) harbor life? A new planetary science report recommends planning a mission to the Saturnian moon to try to answer that question.JPL-Caltech/NASA, Space Science Institute

This proposed spacecraft would arrive at the moon in the early 2050s, where it would first spend 1.5 years orbiting Enceladus, flying through its watery plumes to sample the liquid. Then the spacecraft would land on the surface for a two-year mission.

“If you want to go and look for life, Enceladus is a very good place to do it,” says planetary scientist Francis Nimmo of the University of California, Santa Cruz, and a member of the decadal steering committee.

Life on other planets isn’t the only thing on planetary scientists’ minds. The report also recommends continuing work on a mission to find and characterize near-Earth objects, like asteroids and comets, in an effort to protect life on the only planet where it’s known to exist.

Two medium-sized missions should be funded in the next decade too, the report recommends. While the survey doesn’t specify targets for these missions, nine higher-priority locales are singled out, including Venus, Saturn’s moon Titan and Neptune’s moon Triton.

The decadal survey also considered the state of the fields of planetary science and astrobiology — namely decreasing funding opportunities and how to improve diversity, equity, inclusion and accessibility efforts. For the latter, the committee looked at whether the community has diverse representation through their members.

“The thing that became abundantly clear is that NASA has done a terrible job of collecting those kinds of statistics,” Nimmo says of demographics in planetary science. For now, the recommendation is to better survey the scientific community, he says.  “We’re not going to be able to solve anything until we actually have better statistics.” More

Europa’s frozen surface is covered with distinctive pairs of ridges that straddle troughs of ice. These double ridges are the most common features on the Jovian moon. But scientists don’t yet have a clear idea of how the oddities are created.

Now, an analysis of images of a similar set of ridges on Greenland’s ice sheet suggests that relatively shallow water within Europa’s thick icy shell may be behind their formation, scientists report April 19 in Nature Communications. If so, that could mean that Europa has much more shallow liquid water than scientists have thought.

Europa’s double ridge systems, which can stretch for hundreds of kilometers, include some of the oldest features on the moon, says Riley Culberg, a geophysicist at Stanford University. Some researchers have proposed that the flexing of the moon’s icy shell due to tides in an underlying liquid water ocean plays a role in the ridges’ formation (SN: 8/6/20). Yet others have suggested that water erupted from deep within the icy moon — a process known as cryovolcanism — to create the ridges. Without a closer look, though, it’s been hard to nail down a more solid explanation.

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But Culberg and his colleagues seem to have caught a break. Data gathered by NASA’s ICESat-2 satellite in March 2016 showed an 800-meter-long double ridge system in northwestern Greenland. So the team looked back at other images to see when the ridge system first appeared and to assess how it grew. The researchers found that the ridges appeared in images taken as early as July 2013 and are still there today.

When the ridges — which lie on either side of a trough, like those on Europa — reached full size, they averaged only 2.1 meters high. That’s a lot smaller than the ridges on Europa, which can rise 300 meters or more from the moon’s surface. But surface gravity is much lower on Europa, so ridges can grow much larger there, Culberg says. When he and his colleagues considered the difference between Earth’s gravity and Europa’s in their calculations, they found that the proportions of the two ridge systems are consistent.

Double ridge systems are common on Europa. The largest pair seen in this composite image from NASA’s Galileo spacecraft in the 1990s is about 2.6 kilometers wide and 300 meters tall.JPL-Caltech/NASA, ASU

Scientists will never get a perfect analog of Europa on Earth, but the ridges in Greenland “look just like the Europan ridges,” says Laurent Montési, a geophysicist at the University of Maryland in College Park who was not involved in the study.

Data from airplane-mounted radar gathered in March 2016 show that a water-filled layer of snow about 10 to 15 meters below the surface underlies the Greenland ridges, Culberg and his team say. That water comes from surface meltwater that sinks into and is then collected in the buried snow, which in turn sits atop an impermeable layer of ice.

Repeated freeze-thaw cycles of water in that layer of snow would squeeze water toward the surface, the researchers propose. In the first phase of refreezing, a solid plug of ice forms. Then, as more water freezes, it expands and is forced toward the surface on either side of that plug, pushing material upward and producing the double ridges at the surface.

On Europa, the process works the same way, the researchers suggest. But because there is no known meltwater or precipitation at the moon’s surface, near-surface water there probably would have to come from the ocean thought to be trapped beneath the moon’s icy shell (5/14/18). Once that water rose toward the surface through cracks, it could pool in thick layers of ice shattered by tidal flexing or the impacts of meteorites.

“There’s a general consensus that these ridges grow from cracks in the ice,” says William McKinnon, a planetary scientist at Washington University in Saint Louis who was not involved in the study. “But how do they do it is the question.”

The answer to that question may not be long in coming, McKinnon says. NASA’s Europa Clipper mission is scheduled to launch in late 2024. If all goes well, the orbiter will arrive at Jupiter in April 2030. “If there’s anything like what has happened in Greenland going on at Europa, we’ll be able to see it,” he says.

Researchers will also be interested to see if the mission can ascertain what sort of materials might have been brought to Europa’s surface from the ocean deep below, because the moon is considered to be one of the best places in the solar system to look for extraterrestrial life (SN: 4/8/20). More