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      The dark matter mystery deepens with the demise of a reported detection

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      First of two parts

      In mystery stories, the chief suspect almost always gets exonerated before the end of the book. Typically because a key piece of evidence turned out to be wrong.

      In science, key evidence is supposed to be right. But sometimes it’s not. In the mystery of the invisible “dark matter” in space, evidence implicating one chief suspect has now been directly debunked. WIMPs, tiny particles widely regarded as prime dark matter candidates, have failed to appear in an experiment designed specifically to test the lone previous study claiming to detect them.

      For decades, physicists have realized that most of the universe’s matter is nothing like earthly matter, which is made mostly from protons and neutrons. Gravitational influences on visible matter (stars and galaxies) indicate that some dark stuff of unknown identity pervades the cosmos. Ordinary matter accounts for less than 20 percent of the cosmic matter abundance.

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      For unrelated reasons, theorists have also long suggested that nature possesses mysterious types of tiny particles predicted by a theoretical mathematical framework known as supersymmetry, or SUSY for short. Those particles would be massive by subatomic standards but would interact only weakly with other matter, and so are known as Weakly Interacting Massive particles, hence WIMPs.

      Of the many possible species of WIMPs, one (presumably the lightest one) should have the properties necessary to explain the dark matter messing with the motion of stars and galaxies (SN: 12/27/12). Way back in the last century, searches began for WIMPs in an effort to demonstrate their existence and identify which species made up the dark matter.

      In1998, one research team announced apparent success. An experiment called DAMA (for DArk MAtter, get it?), consisting of a particle detector buried under the Italian Alps, seemingly did detect particles with properties matching some physicists’ expectations for a dark matter signal.

      It was a tricky experiment to perform, relying on the premise that space is full of swarms of WIMPs. A detector containing chunks of sodium iodide should give off a flash of light when hit by a WIMP. But other particles from natural radioactive substances would also produce flashes of light even if WIMPs are a myth.

      So the experimenters adopted a clever suggestion proposed earlier by physicists Katherine Freese, David Spergel and Andrzej Drukier, known formally as an annual modulation test. But let’s just call it the June-December approach.

      As the Earth orbits the sun, the sun also moves, traveling around the Milky Way galaxy, carried by a spiral arm in the direction of the constellation Cygnus. If the galaxy really is full of WIMPs, the sun should be constantly plowing through them, generating a “WIMP wind.” (It’s like the wind you feel if you stick your head out of the window of a moving car.) In June, the Earth’s orbit moves it in the same direction as the sun’s motion around the galaxy — into the wind. But in December, the Earth moves the opposite direction, away from the wind. So more WIMPs should be striking the Earth in June than in December. It’s just like the way your car windshield smashes into more raindrops when driving forward than when going in reverse.

      As the sun moves through space, it should collide with dark matter particles called WIMPs, if they exist. When the Earth’s revolution carries it in the same direction as the sun, in summer, the resulting “WIMP wind” should appear stronger, with more WIMP collisions detected in June than in December.GEOATLAS/GRAPHI-OGRE, ADAPTED BY T. DUBÉ

      At an astrophysics conference in Paris in December 1998, Pierluigi Belli of the DAMA team reported a clear signal (or at least a strong hint) that more particles arrived in June than December. (More precisely, the results showed an annual modulation in frequency of light flashes, peaking around June with a minimum in December.) The DAMA data indicated a WIMP weighing in at 59 billion electron volts, roughly 60 times the mass of a proton.

      But some experts had concerns about the DAMA team’s data analysis. And other searches for WIMPs, with different detectors and strategies, should have found WIMPs if DAMA was right — but didn’t. Still, DAMA persisted. An advanced version of the experiment, DAMA/LIBRA, continued to find the June-December disparity.

      Perhaps DAMA was more sensitive to WIMPs than other experiments. After all, the other searches did not duplicate DAMA’s methods. Some used substances other than sodium iodide as a detecting material, or watched for slight temperature increases as a sign of a WIMP collision rather than flashes of light.

      For that matter, WIMPs might not be what theorists originally thought. DAMA initially reported 60 proton-mass WIMPs based on the belief that the WIMPs collided with iodine atoms. But later data suggested that perhaps the WIMPs were hitting sodium atoms, implying a much lighter WIMP mass — lighter than other experiments had been optimally designed to detect. Yet another possibility: Maybe trace amounts of the metallic element thallium (much heavier atoms than either iodine or sodium) had been the WIMP targets. But a recent review of that proposal found once again that the DAMA results could not be reconciled with the absence of a signal in other experiments.

      And now DAMA’s hope for vindication has been further dashed by a new underground experiment, this one in Spain. Scientists with the ANAIS collaboration have repeated the June-December method with sodium iodide, in an effort to reproduce DAMA’s results with the same method and materials. After three years of operation, the ANAIS team reports no sign of WIMPs.

      To be fair, the no-WIMP conclusion relies on a lot of seriously sophisticated technical analysis. It’s not just a matter of counting light flashes. You have to collect rigorous data on the behavior of nine different sodium iodide modules. You have to correct for the presence of rare radioactive isotopes generated by cosmic ray collisions while the modules were still under construction. And then the statistical analysis needed to discern a winter-summer signal difference is not something you should try at home (unless you’re fully versed in things like the least-square periodogram or the Lomb-Scargle technique). Plus, ANAIS it still going, with plans to collect two more years of data before issuing a final analysis. So the judgment on DAMA’s WIMPs is not necessarily final.

      Nevertheless, it doesn’t look good for WIMPs, at least for the WIMPs motivated by belief in supersymmetry.   

      Sadly for SUSY fans, searches for WIMPs from space are not the only bad news. Attempts to produce WIMPs in particle accelerators have also so far failed. Dark matter might just turn out to consist of some other kind of subatomic particle.

      If so, it would be a plot twist worthy of Agatha Christie, kind of like Poirot turning out to be the killer. For symmetry has long been physicists’ most reliable friend, guiding many great successes, from Einstein’s relativity theory to the standard model of particles and forces.

      Still, failure to find SUSY particles so far does not necessarily mean they don’t exist. Supersymmetry just might be not as simple as it first seemed. And SUSY particles might just be harder to detect than scientists originally surmised. But if supersymmetry does turn out not to be so super, scientists might need to reflect on the ways that faith in symmetry can lead them astray. More

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      Carbon-ring molecules tied to life were found in space for the first time

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      Complex carbon-bearing molecules that could help explain how life got started have been identified in space for the first time.

      These molecules, called polycyclic aromatic hydrocarbons, or PAHs, consist of several linked hexagonal rings of carbon with hydrogen atoms at the edges. Astronomers have suspected for decades that these molecules are abundant in space, but none had been directly spotted before.

      Simpler molecules with a single ring of carbon have been seen before. But “we’re now excited to see that we’re able to detect these larger PAHs for the first time in space,” says astrochemist Brett McGuire of MIT, whose team reports the discovery in the March 19 Science.

      Studying these molecules and others like them could help scientists understand how the chemical precursors to life might get started in space. “Carbon is such a fundamental part of chemical reactions, especially reactions leading to life’s essential molecules,” McGuire says. “This is our window into a huge reservoir of them.”

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      Since the 1980s, astronomers have seen a mysterious infrared glow coming from spots within our galaxy and others. Many suspected that the glow comes from PAHs, but could not identify a specific source. The signals from several different PAHs overlap too much to tease any one of them apart, like a choir blending so well, the ear can’t pick out individual voices.

      Instead of searching the infrared signals for a single voice, McGuire and colleagues turned to radio waves, where different PAHs sing different songs. The team trained the powerful Green Bank Telescope in West Virginia on TMC-1, a dark cloud about 430 light-years from Earth near the constellation Taurus.

      The interstellar cloud TMC-1 (top, black filaments) appears as a dark streak on the sky next to the bright Pleiades star cluster (right)Brett A. McGuire

      Previously, McGuire had discovered that the cloud contains benzonitrile, a molecule made of a single carbon ring (SN: 10/2/19). So he thought it was a good place to look for more complicated molecules.

      The team detected 1- and 2-cyanonaphthalene, two-ringed molecules with 10 carbons, eight hydrogens and a nitrogen atom. The concentration is fairly diffuse, McGuire says: “If you filled the inside of your average compact car with [gas from] TMC-1, you’d have less than 10 molecules of each PAH we detected.”

      But it was a lot more than the team expected. The cloud contains between 100,000 and one million times more PAHs than theoretical models predict it should. “It’s insane, that’s way too much,” McGuire says.

      There are two ways that PAHs are thought to form in space: out of the ashes of dead stars or by direct chemical reactions in interstellar space. Since TMC-1 is just beginning to form stars, McGuire expected that any PAHs it contains ought to have been built by direct chemical reactions in space. But that scenario can’t account for all the PAH molecules the team found. There’s too much to be explained easily by stellar ash, too. That means something is probably missing from astrochemists’ theories of how PAHs can form in space.

      “We’re working in uncharted territory here,” he says, “which is exciting.”

      Identifying PAHs in space is “a big thing,” says astrochemist Alessandra Ricca of the SETI Institute in Mountain View, Calif., who was not involved in the new study. The work “is the first one that has shown that these PAH molecules actually do exist in space,” she says. “Before, it was just a hypothesis.”

      Ricca’s group is working on a database of infrared PAH signals that the James Webb Space Telescope, slated to launch in October, can look for. “All this is going to be very helpful for JWST and the research on carbon in the universe,” she says. More

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      ‘Oumuamua may be a chip knocked off an icy, Pluto-like exoplanet

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      Since its discovery, the interstellar object known as ‘Oumuamua has defied explanation. First spotted in 2017, it has been called an asteroid, a comet and an alien spaceship (SN: 10/27/17). But researchers think they finally have the mystery object pegged: It could be a shard of nitrogen ice broken off a Pluto-like planet orbiting another star.

      “The idea is pretty compelling,” says Garrett Levine, an astronomer at Yale University not involved in the work. “It does a really good job of matching the observations.”

      ‘Oumuamua’s origin has been a mystery because it looks sort of like a comet, but not quite (SN: 12/18/17). After whipping by the sun, ‘Oumuamua zoomed away slightly faster than gravity alone would allow. That happens when ices on the sunlit sides of comets vaporize, giving them a little rocketlike boost in speed. But unlike comets, ‘Oumuamua didn’t appear to have a tail from typical cometary ices, such as carbon monoxide or carbon dioxide, streaming off it.

      Alan Jackson and Steven Desch, planetary scientists at Arizona State University in Tempe, set out to discover what other kind of evaporating ice could give ‘Oumuamua a big enough nudge to explain its movement. The pair reported their results March 17 at the virtual Lunar and Planetary Science Conference and in two studies published online March 16 in the Journal of Geophysical Research: Planets.

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      The amount of force that a vaporizing ice exerts on a comet depends on factors such as how much the ice heats up when it absorbs energy, the mass of its molecules and even the ice’s crystal structure. By calculating the rocketlike push on ‘Oumuamua if it were made of ices such as nitrogen, hydrogen and water, “we learned that nitrogen ice would work perfectly well,” Desch says.

      Because nitrogen ice covers outer solar system bodies such as Pluto and Neptune’s moon Triton, but not smaller objects like comets, ‘Oumuamua is probably a chip off a Pluto-like exoplanet, the researchers report.

      To determine how realistic that scenario is, Jackson and Desch calculated how many chunks of nitrogen ice could have been knocked off Pluto-like bodies in the early solar system. Back then, the Kuiper Belt of objects beyond Neptune was much more crowded than it is today, including thousands of Pluto-like bodies iced with nitrogen. But some 4 billion years ago, Neptune’s orbit expanded. That disruption caused many Kuiper Belt objects to collide with each other, and most sailed out of the solar system altogether.

      Under such chaotic conditions, collisions could have broken trillions of nitrogen ice fragments off Pluto-like bodies, Jackson and Desch estimate. If other planetary systems throw out as many shards of ice, those objects could make up about 4 percent of the bodies in interstellar space. That would make seeing an object like ‘Oumuamua mildly unusual but not exceptional, the researchers say.

      “When I first started reading it, I was skeptical … but it does tick a lot of the necessary boxes,” says Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington, D.C. not involved in the work. “It’s definitely plausible that this could be a fragment of an icy dwarf planet.” But plausible, he notes, does not necessarily mean correct.

      ‘Oumuamua is now too far away to confirm this idea with more observations. But the upcoming Vera Rubin Observatory and European Space Agency’s Comet Interceptor mission could detect more interstellar objects, says Yun Zhang, a planetary scientist at Côte d’Azur Observatory in Nice, France not involved in the research. The Vera Rubin Observatory is expected to spot, on average, one interstellar visitor per year, and the Comet Interceptor spacecraft may actually visit one.

      Getting a closer look at more of these objects could narrow down which possible explanations for ‘Oumuamua are most reasonable, she says (SN: 2/27/19). More

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      A gargantuan supernova remnant looks 40 times as big as the full moon

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      A cloud of expanding gas in space is the largest supernova remnant ever seen in the sky, a new study confirms.

      The Milky Way has some 300 known supernova remnants, each made of debris from an exploded star mixed with interstellar material swept up by the blast. This supersized one, located in the constellation Antlia, isn’t necessarily the biggest of all physically, but thanks to its proximity to us, it looks the biggest. As seen from Earth, it spans a region of sky more than 40 times the size of a full moon, astronomer Robert Fesen of Dartmouth College and his colleagues report February 25 at arXiv.org. The Antlia remnant appears about three times as large as the previous champion, the Vela supernova remnant (SN: 7/8/20).

      The star that created the Antlia supernova remnant exploded roughly 100,000 years ago. Estimates of the remnant’s distance vary, so its physical size has yet to be nailed down. But if the cloud is 1,000 light-years away, then it’s about 390 light-years across; if it’s twice as far, then it’s twice as big. Either way, it’s considerably larger than the Vela supernova remnant, which is about 100 light-years wide.

      Vela (shown) had been the largest confirmed supernova remnant as seen from Earth, but the one in Antlia looks three times larger.Robert Gendler, Roberto Colombari, Digitized Sky Survey (POSS II)

      The Antlia remnant isn’t new to astronomers. In 2002, researchers discovered the cloud and proposed that it is the nearby remains of a supernova, based on the red glow of its hydrogen atoms as well as its X-ray emission. But hardly anyone had observed the object since. “It wasn’t really firmly established as a supernova remnant,” says team member John Raymond, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

      So the astronomers studied the cloud at visible and ultraviolet wavelengths, which demonstrate that the Antlia object is indeed a supernova remnant. In particular, the visible light shows spectral signatures of shock waves, which result when high-speed gas from a supernova slams into gas around it.

      “The evidence for it being shocks in a supernova remnant seems to be very good,” says Roger Chevalier, an astronomer at the University of Virginia in Charlottesville not involved with the new work. He notes that the team detected red light from sulfur atoms that are missing one electron, a hallmark of shocks in supernova remnants.

      The astronomer who discovered the object two decades ago had little doubt it was a genuine supernova remnant. “They’ve done good work,” says Peter McCullough at the Space Telescope Science Institute in Baltimore. “This is a case where it looks like a duck, quacks like a duck, walks like a duck and now someone else 20 years later comes along and says, `Not only that, it has feathers.’” More

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      Most of Mars’ missing water may lurk in its crust

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      An ocean’s worth of water may be lurking in minerals below Mars’ surface, which could help explain why the Red Planet dried up.

      Once home to lakes and rivers, Mars is now a frigid desert (SN: 12/8/14). Scientists have typically blamed that on Mars’ water wafting out of the planet’s atmosphere into space (SN: 11/12/20). But measurements of atmospheric water loss made by spacecraft like NASA’s MAVEN orbiter are not enough to account for all of Mars’ missing water — which was once so abundant it could have covered the whole planet in a sea up to 1,500 meters deep. That’s more than half the volume of the Atlantic Ocean.

      Computer simulations of water moving through Mars’ interior, surface and atmosphere now suggest that most of the Red Planet’s water molecules may have gotten lodged inside the crystal structures of minerals in the planet’s crust, researchers report online March 16 in Science. 

      The finding “helps bring focus to a really important mechanism for water loss on Mars,” says Kirsten Siebach, a planetary geologist at Rice University in Houston who was not involved in the work. “Water getting locked up in crustal minerals may be equally important as water loss to space and could potentially be more important.”

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      Planetary scientist Eva Scheller of Caltech and colleagues simulated possible scenarios for water loss on Mars, based on observations of the Red Planet made by rovers and orbiting spacecraft, and lab analyses of Martian meteorites. These simulations accounted for possible water loss to space and into the planet’s crust through bodies of water or groundwater interacting with rock.

      In order for the simulations to match how much water was on Mars 4 billion years ago, how much is left in polar ice caps today and the observed abundance of hydrogen in Mars’ atmosphere, 30 to 99 percent of Mars’ ancient water must be stashed away inside its crust. The rest was lost to space.

      Judging by modern Martian landscapes, like this image taken by the Curiosity rover at the base of Mount Sharp, the Red Planet appears bone dry. But an entire ocean’s worth of water may be lurking underground, in the minerals of the planet’s crust.MSSS/JPL-Caltech/NASA

      Water gets locked inside minerals on Earth, too, says Scheller, who presented the results March 16 in a news conference at the virtual Lunar and Planetary Science Conference. But unlike on Mars, that underground water is eventually belched back out into the atmosphere by volcanoes. That difference is important for understanding why one rocky planet may be lush and wet and habitable, while another is an arid wasteland. 

      Mars’ underground water could be mined by future explorers, says Jack Mustard, a planetary geologist at Brown University in Providence, R.I., not involved in the work. The most easily accessible water on Mars may be at its polar ice caps (SN: 9/28/20). But “to get the ice, you’ve got to go up to [high latitudes] — kind of cold, harder to live there,” Mustard says. If water can be extracted from minerals, it could support human colonies at warmer climes closer to the equator.  More

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      Andromeda’s and the Milky Way’s black holes will collide. Here’s how it may play out

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      The supermassive black holes at the centers of the Milky Way and Andromeda galaxies are doomed to engulf each other in an ill-fated cosmological dance.
      Astronomers have long known that Andromeda is on a collision course with our galaxy (SN: 5/31/12). But not much has been known about what will happen to the gargantuan black holes each galaxy harbors at its core. New simulations reveal their ultimate fate.
      The galaxies will coalesce into one giant elliptical galaxy — dubbed “Milkomeda” — in about 10 billion years. Then, the central black holes will begin orbiting one another and finally collide less than 17 million years later, researchers propose February 22 at arXiv.org and in an earlier paper published in Astronomy & Astrophysics. Just before the black holes smash into each other, they’ll radiate gravitational waves with the power of 10 quintillion suns (SN: 2/11/16). Any civilization within 3.25 million light-years from us that has gravitational wave–sensing technology on par with our current abilities would be able to detect the collision, the researchers estimate.
      The latest data suggest Andromeda is approaching us at about 116 kilometers per second, says Riccardo Schiavi, an astrophysicist at the Sapienza University of Rome. Using computer simulations that include the gravitational pull of the two spiral galaxies on each other as well as the possible presence of sparse gas and other material between them, Schiavi and his colleagues played out how the galactic collision will unfold.
      [embedded content]
      A computer simulation shows how the Milky Way (left) and Andromeda (right) galaxies will brush past each other about 4 billion years from now before merging into a single galaxy roughly 6 billion years later. The numbers along the sides denote distance in kiloparsecs (1 kiloparsec equals 3,260 light-years).
      Previous simulations have suggested that Andromeda and the Milky Way are scheduled for a head-on collision in about 4 billion to 5 billion years. But the new study estimates that the two star groups will swoop closely past each other about 4.3 billion years from now and then fully merge about 6 billion years later.
      The team’s estimate for Milkomeda’s merger date “is a bit longer than what other teams have found,” says Roeland van der Marel, an astronomer at the Space Telescope Science Institute in Baltimore who was not involved in the research. However, he notes, that could be due in part to uncertainty in the measurement of Andromeda’s speed across the sky. More

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      Black hole visionaries push the boundaries of knowledge in a new film

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      Black holes sit on the cusp of the unknowable. Anything that crosses a black hole’s threshold is lost forever, trapped by an extreme gravitational pull. That enigmatic quality makes the behemoths an enticing subject, scientists explain in the new documentary Black Holes: The Edge of All We Know.
      The film follows two teams working over the last several years to unveil the mystery-shrouded monstrosities. Scientists with the Event Horizon Telescope attempt to make the first image of a black hole’s shadow using a global network of telescopes. Meanwhile, a small group of theoretical physicists, anchored by Stephen Hawking — who was still alive when filming began — aim to solve a theoretical quandary called the black hole information paradox (SN: 5/16/14).
      When big discoveries happen, the camera is right there — allowing us to thrill in the moment when Event Horizon Telescope scientists first lay eyes on a black hole’s visage. And we triumph as the team unveils the result in 2019, a now-familiar orange, ring-shaped image depicting the supermassive black hole in the center of galaxy M87 (SN: 4/10/19). Likewise, scenes where Hawking questions his collaborators as they explain chalkboards full of equations prove mesmerizing. Viewers witness brilliant minds playing off one another, struggling with mistakes and dead ends in their calculations, punctuated by occasional, groundbreaking progress.
      [embedded content]
      Watch the trailer for Black Holes: The Edge of All We Know.
      Stunning cinematography and skillful editing lend energy to Black Holes, directed by Harvard physicist and historian Peter Galison and available on Apple TV, Amazon Prime Video and other on-demand platforms on March 2. When the Event Horizon Telescope team begins taking data, we’re treated to a crisp montage of telescopes around the world, all swiveling to catch a glimpse of the black hole. Later, bright sunbeams slice across an office floor while scientists muddle through calculations regarding the darkest objects of the cosmos. Such scenes are punctuated by delightfully strange black-and-white animations that evoke a pensiveness appropriate for contemplating cosmic oddities.

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      There’s drama too: Event Horizon Telescope’s scientists wrestle with misbehaving equipment and curse uncooperative weather. The theoretical physicists grapple with the immense complexity of the cosmos on slow, distracted walks in the forest.
      Other research topics garner brief mentions, such as the study of gravitational waves from colliding black holes (SN: 1/21/21) and black hole analogs made using water vortices (SN 6/12/17). The film treats these varied efforts to study black holes independently; some viewers may wish the dots were better connected.
      The film Black Holes: The Edge of All We Know features this water vortex, lit by green light. Scientists used such vortices along with other techniques to re-create the physics of black holes.Giant Pictures
      Still, Black Holes successfully leads viewers through a fascinating, understandable trek across the varied frontiers of black hole knowledge. As Harvard physicist Shep Doeleman of the Event Horizon Telescope team describes it in the film, “we are chasing down something that struggles with all of its might to be unseen.” Pulling us to the very rim of this fathomless abyss, Black Holes invites us to stand with scientists peering over the edge. More

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      Watch real video of Perseverance’s Mars landing

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      This is what it looks like to land on Mars.
      NASA’s Perseverance rover took this video on February 18 as a jetpack lowered it onto the Red Planet’s surface.
      “It gives me goosebumps every time I see it,” said engineer David Gruel of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., at a news briefing on February 22.
      The movie begins with the rover’s parachute opening above it as the rover and its landing gear enter the Martian atmosphere. Seconds later, a camera on the rover’s underside shows the heat shield falling toward the ground. If you look carefully, you can see one of the springs that pushed the heat shield off the rover came loose, said NASA engineer Allen Chen, the rover’s entry, descent and landing lead.
      [embedded content]
      NASA’s Perseverance rover captured video of its own landing using a set of cameras on the back of the entry vehicle, the sky crane and the rover itself.
      “There’s no danger to the spacecraft here, but it’s something we didn’t expect, and wouldn’t have seen” without the videos, he said.
      The rover filmed the ground coming closer and closer, getting glimpses of a river delta, craters, ripples and fractured terrain. Cameras on the top and bottom of the rover captured clouds of dust billowing as the rover’s jetpack, the sky crane, lowered it down to the ground on three cables. A camera on the sky crane showed the rover swinging slightly as it descended. Finally, the sky crane disconnected the cables and flew away, leaving Perseverance to begin its mission.
      “It’s hard to express how emotional it was and how exciting it was to everybody” to see the movie for the first time, said deputy project manager Matt Wallace. “Every time we got something, people were overjoyed, giddy. They were like kids in a candy store.”
      The movie looks so much like animations of the sky crane landing technique that NASA had released in the past that it almost doesn’t look real, says imaging scientist Justin Maki. “I can attest to, it’s real,” he says. “It’s stunning and it’s real.”

      The rover also captured audio from the surface of the Red Planet for the first time, including a gust of Martian wind.
      Perseverance landed in an ancient lakebed called Jezero crater, about two kilometers from what looks like an ancient river delta feeding into the crater (SN: 2/18/21). The rover’s primary mission is to search for signs of past life and to cache rock samples for a future mission to return to Earth.
      The first images Perseverance sent back from Mars showed its wheels on a flat expanse. The ground is strewn with rocks that are shot through with holes, said deputy project scientist Katie Stack Morgan in a news briefing on February 19.
      “Depending on the origins of the rocks, these holes could mean different things,” she said. The science team thinks the holes could be from gases escaping volcanic rock as lava cooled, or from fluid moving through the rock and dissolving it away. “Both would be equally exciting for the team.”

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