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    Samples of the asteroid Ryugu are scientists’ purest pieces of the solar system

    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

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    Ice at the moon’s poles might have come from ancient volcanoes

    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

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    NASA’s InSight lander has recorded the largest Marsquake yet

    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

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    This is the biggest known comet in our solar system

    The nucleus of a comet discovered in 2014 is the largest ever spotted.

    The “dirty snowball” at the center of comet C/2014 UN271 is about 120 kilometers across, researchers report in the April 10 Astrophysical Journal Letters. That makes this comet — also known as Bernardinelli-Bernstein, after its discoverers — about twice as wide as Rhode Island, says David Jewitt, an astronomer at UCLA.

    Though the comet is big — and vastly larger than Halley’s comet, which measures a little more than 11 kilometers across — it will never be visible to the naked eye from Earth because it’s too far away, Jewitt says (SN: 12/14/15). The object is now about 3 billion kilometers from Earth. At its closest approach in 2031, the comet will come no closer to the sun than 1.6 billion kilometers, about the same distance as Saturn.

    Jewitt and colleagues sized up the comet with the help of new images from the Hubble Space Telescope, combined with images taken by another team at far-infrared wavelengths. The analysis also revealed that the comet’s nucleus reflects only about 3 percent of the light that strikes it. That makes the object “blacker than coal,” Jewitt says.

    Comet Bernardinelli-Bernstein takes about 3 million years to circle the sun in a highly elliptical orbit. At its farthest, the comet may reach about half a light-year from the sun — about one-eighth of the distance to the next nearest star.

    The comet is likely “just the tip of the iceberg” as far as undiscovered comets of this size go, Jewitt says. And for every comet this size, he suggests, there could be tens of thousands of smaller objects circling the sun undetected.

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    New thermal maps of Neptune reveal surprising temperature swings

    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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    Mars has two speeds of sound

    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

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    Diamonds may stud Mercury’s crust

    A treasure trove of diamonds may be sown into Mercury’s cratered crust.

    Billions of years of meteorite impacts may have flash-baked much of Mercury’s surface into the glittery gemstones, planetary scientist Kevin Cannon reported March 10 at the Lunar and Planetary Science Conference in The Woodlands, Texas. His computer simulations predict that such impacts may have transformed about one-third of the little planet’s crust into a diamond stockpile many times that of Earth’s.

    Diamonds are forged under immense pressures and temperatures. On Earth, the gemstones crystallize deep underground — at least 150 kilometers down — then ride to the surface during volcanic eruptions (SN: 9/14/20). But studies of meteorites suggest diamonds can also form during impact.

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    “When those [impacts] happen, they create very high pressures and temperatures that can transform carbon into diamond,” says Cannon, of the Colorado School of Mines in Golden.

    With impact-born diamonds on his mind, Cannon turned to the closest planet to the sun. Surveys of the planet’s surface and experiments with molten rock suggest that the planet’s crust may retain fragments of an old shell of graphite — a mineral made from carbon (SN: 3/7/16). “What we think happened is that when [Mercury] first formed, it had a magma ocean, and that graphite crystallized out of that magma,” Cannon says.

    Then, the bombardment. Mercury’s surface today is heavily cratered, evidence of an impact-rich history. Much of the purported graphite crust would have been battered and transformed into diamond, Cannon hypothesized.

    Curious how pervasive this diamond forging could have been, Cannon used computers to simulate 4.5 billion years of impacts on a graphite crust. The findings show that if Mercury had possessed a skin of graphite 300 meters thick, the battering would have generated 16 quadrillion tons of diamonds — about 16 times Earth’s estimated reserves.

    “There’s no reason to doubt that diamonds could be produced in this way,” says Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colo., who was not involved with the research. But how many might have survived, that’s another story, he says. Some of the gemstones would probably have been destroyed by later impacts.

    Cannon agrees that subsequent impacts would probably obliterate some diamonds. But the losses would have been “very limited,” he says, as the ultimate melting point of diamond exceeds 4000° Celsius. Future simulations will incorporate remelting from impacts, he says, to refine the potential size of Mercury’s present day diamond reserves.

    An opportunity to scout for diamonds on Mercury may come in 2025, when the BepiColombo mission reaches the planet. Diamonds reflect a distinct signature of infrared light, Cannon says. “And potentially, this could be detected.” More

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    An ancient impact on Earth led to a cascade of cratering

    A bevy of craters formed by material blasted from the carving of another, larger crater — a process dubbed secondary cratering — have finally been spotted on Earth. Several groupings of craters in southeastern Wyoming, including dozens of pockmarks in all, have the hallmarks of secondary cratering, researchers report February 11 in GSA Bulletin.

    When an asteroid or another type of space rock smacks into a planet or moon, it blasts material from the surface and creates a crater (SN: 12/18/18). Large blocks of that material can be thrown far from the initial crater and blast out their own holes when they land, explains Thomas Kenkmann, a planetary scientist at the Albert Ludwig University of Freiburg in Germany. Astronomers have long observed secondary cratering on our moon, Mars and other orbs in the solar system, but never on Earth.

    When Kenkmann and his colleagues first investigated a series of craters near Douglas, Wyo., in 2018, they thought the pockmarks were formed by fragments of a large meteorite that had broken up in the atmosphere. But Kenkmann and his team later discovered similar groups of craters of the same age, somewhere around 280 million years old, throughout the region.

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    Altogether, the team found more than 30 impact craters that range between 10 and 70 meters in diameter at six different locales. Based on subtle but distinct differences in the alignment of elliptical craters in the groups, the researchers suggest that the impactors that blasted each set of craters struck the ground from slightly different directions.

    The impactors that created these secondary craters probably ranged between 4 and 8 meters in diameter and struck the ground at speeds between 2,520 and 3,600 kilometers per hour, Kenkmann says. Extrapolating the paths of these impactors back to their presumed sources suggests the original crater from which they flew straddles the Wyoming–Nebraska border northeast of Cheyenne.

    The team’s evidence “comes together very well to make a compelling story,” says Gareth Collins, a planetary scientist at Imperial College London who was not involved in the new study.

    The original crater was probably between 50 and 65 kilometers across and was created by an impactor 4 to 5.4 kilometers wide, Kenkmann and the team estimate. The crater is also probably buried under more than 2 kilometers of sediment that accumulated in the 280 million years since it formed. An equivalent amount of sediment eroded away to expose the secondary craters when the Rocky Mountains rose in the meantime.

    “What a fortuitous discovery that these folks have made,” says Beau Bierhaus, a planetary scientist at Lockheed Martin Space Systems in Littleton, Colo. He likens the short geological interval during which these craters could be discovered to the brief period between the time a fossil is first exposed to the elements and when it is eroded to dust.

    Scouring measurements of gravitational and magnetic fields in the region for anomalies could help reveal the buried crater, the researchers note. The team may also look for heavily fractured rock and other evidence of the ancient crater in sediment cores that have been drilled during oil and gas exploration in the region, Kenkmann says. More