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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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      Signs of a hidden Planet Nine in the solar system may not hold up

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      Planet Nine might be a mirage. What once looked like evidence for a massive planet hiding at the solar system’s edge may be an illusion, a new study suggests.
      “We can’t rule it out,” says Kevin Napier, a physicist at the University of Michigan in Ann Arbor. “But there’s not necessarily a reason to rule it in.”
      Previous work has suggested that a number of far-out objects in the solar system cluster in the sky as if they are being shepherded by an unseen giant planet, at least 10 times the mass of Earth. Astronomers dubbed the invisible world Planet Nine or Planet X.
      Now, a new analysis of 14 of those remote bodies shows no evidence for such clustering, knocking down the primary reason to believe in Planet Nine. Napier and colleagues reported the results February 10 at arXiv.org in a paper to appear in the Planetary Science Journal.

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      The idea of a distant planet lurking far beyond Neptune received a surge in interest in 2014, when astronomers Chad Trujillo of Northern Arizona University and Scott Sheppard of the Carnegie Institution for Science reported a collection of distant solar system bodies called trans-Neptunian objects with strangely bunched-up orbits (SN: 11/14/14).
      In 2016, Caltech planetary scientists Mike Brown and Konstantin Batygin used six trans-Neptunian objects to refine the possible properties of Planet Nine, pinning it to an orbit between 500 and 600 times as far from the sun as Earth’s (SN: 7/5/16).
      But those earlier studies all relied on just a handful of objects that may not have represented everything that’s out there, says Gary Bernstein, an astronomer at the University of Pennsylvania. The objects might have seemed to show up in certain parts of the sky only because that’s where astronomers happened to look.
      “It’s important to know what you couldn’t see, in addition to what you did see,” he says.
      To account for that uncertainty, Napier, Bernstein and colleagues combined observations from three surveys — the Dark Energy Survey, the Outer Solar System Origins Survey and the original survey run by Sheppard and Trujillo — to assess 14 trans-Neptunian objects, more than twice as many as in the 2016 study. These objects all reside between 233 and 1,560 times as far from the sun as Earth.
      The team then ran computer simulations of about 10 billion fake trans-Neptunian objects, distributed randomly all around the sky, and checked to see if their positions matched what the surveys should be able to see. They did.
      “It really looks like we just find things where we look,” Napier says. It’s sort of like if you lost your keys at night and searched for them under a streetlamp, not because you thought they were there, but because that’s where the light was. The new study basically points out the streetlamps.
      “Once you see where the lampposts really are, it becomes more clear that there is some serious selection bias going on with the discovery of these objects,” Napier says. That means the objects are just as likely to be distributed randomly across the sky as they are to be clumped up.
      That doesn’t necessarily mean Planet Nine is done for, he says.
      “On Twitter, people have been very into saying that this kills Planet Nine,” Napier says. “I want to be very careful to mention that this does not kill Planet Nine. But it’s not good for Planet Nine.”
      There are other mysteries of the solar system that Planet Nine would have neatly explained, says astronomer Samantha Lawler of the University of Regina in Canada, who was not involved in the new study. A distant planet could explain why some far-out solar system objects have orbits that are tilted relative to those of the larger planets or where proto-comets called centaurs come from (SN: 8/18/20). That was part of the appeal of the Planet Nine hypothesis.
      “But the entire reason for it was the clustering of these orbits,” she says. “If that clustering is not real, then there’s no reason to believe there is a giant planet in the distant solar system that we haven’t discovered yet.”
      Batygin, one of the authors of the 2016 paper, isn’t ready to give up. “I’m still quite optimistic about Planet Nine,” he says. He compares Napier’s argument to seeing a group of bears in the forest: If you see a bunch of bears to the east, you might think there was a bear cave there. “But Napier is saying the bears are all around us, because we haven’t checked everywhere,” Batygin says. “That logical jump is not one you can make.”
      Evidence for Planet Nine should show up only in the orbits of objects that are stable over billions of years, Batygin adds. But the new study, he says, is “strongly contaminated” by unstable objects — bodies that may have been nudged by Neptune and lost their position in the cluster or could be on their way to leaving the solar system entirely. “If you mix dirt with your ice cream, you’re going to mostly taste dirt,” he says.
      Lawler says there’s not a consensus among people who study trans-Neptunian objects about which ones are stable and which ones are not.
      Everyone agrees, though, that in order to prove Planet Nine’s existence or nonexistence, astronomers need to discover more trans-Neptunian objects. The Vera Rubin Observatory in Chile should find hundreds more after it begins surveying the sky in 2023 (SN: 1/10/20).
      “There always may be some gap in our understanding,” Napier says. “That’s why we keep looking.” More

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      The first black hole ever discovered is more massive than previously thought

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      The first black hole ever discovered still has a few surprises in store.
      New observations of the black hole–star pair called Cygnus X-1 indicate that the black hole weighs about 21 times as much as the sun — nearly 1.5 times heavier than past estimates. The updated mass has astronomers rethinking how some black hole–forming stars evolve. For a star-sized, or stellar, black hole that massive to exist in the Milky Way, its parent star must have shed less mass through stellar winds than expected, researchers report online February 18 in Science.
      Knowing how much mass stars lose through stellar winds over their lifetimes is important for understanding how these stars enrich their surroundings with heavy elements. It’s also key to understanding the masses and compositions of those stars when they explode and leave behind black holes.
      The updated mass measurement of Cygnus X-1 is “a big change to an old favorite,” says Tana Joseph, an astronomer at the University of Amsterdam not involved in the work. Stephen Hawking famously bet physicist Kip Thorne that the Cygnus X-1 system, discovered in 1964, did not include a black hole — and conceded the wager in 1990, when scientists had broadly accepted that Cygnus X-1 contained the first known black hole in the universe (SN: 4/10/19).

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      Astronomers got a new look at Cygnus X-1 using the Very Long Baseline Array, or VLBA. This network of 10 radio dishes stretches across the United States, from Hawaii to the Virgin Islands, collectively forming a continent-sized radio dish. In 2016, the VLBA tracked radio-bright jets of material spewing out of Cygnus X-1’s black hole for six days (the time it took for the black hole and its companion star to orbit each other once). Those observations offered a clear view of how the black hole’s position in space shifted over the course of its orbit. That, in turn, helped researchers refine the estimated distance to Cygnus X-1.
      The new observations suggest that Cygnus X-1 is about 7,200 light-years from Earth, rather than the previous estimate of about 6,000 light-years. This implies that the star in Cygnus X-1 is even brighter, and therefore bigger, than astronomers thought. The star weighs about 40.6 suns, the researchers estimate. The black hole must also be more massive in order to explain its gravitational tug on such a massive star. The black hole weighs about 21.2 suns — much heftier than its previously estimated 14.8 solar masses, the scientists say. 
      The new mass measurement for Cygnus X-1’s black hole is so big that it challenges astronomers’ understanding of the massive stars that collapse to form black holes, says study coauthor Ilya Mandel, an astrophysicist at Monash University in Melbourne, Australia.
      “Sometimes stars are born with quite high masses — there are observations of stars being born with masses of well over 100 solar masses,” Mandel says. But such enormous stars are thought to shed much of their weight through stellar winds before turning into black holes. The bigger the star and the more heavy elements it contains, the stronger its stellar winds. So in heavy element–rich galaxies such as the Milky Way, big stars — no matter their starting mass — are supposed to shrink down to about 15 solar masses before collapsing into black holes.
      Cygnus X-1’s 21-solar-mass black hole undermines that idea.
      The LIGO and Virgo gravitational wave detectors have discovered black holes weighing tens of solar masses in other galaxies (SN: 1/21/21). But that is probably because LIGO peers at distant galaxies that existed earlier in the universe, Joseph says. Back then, fewer heavy elements existed, so stellar winds were weaker. With the new Cygnus X-1 measurement, “now we have to say, hang on, we’re in a [heavy element]–rich environment compared to the early universe … but we still managed to make this really massive black hole,” she says, “so maybe we’re not losing as much mass through stellar winds as we initially thought.” More

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      Here’s how to watch NASA’s Perseverance lander touch down on Mars

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      All eyes are on Mars — and all ears, too. When NASA’s Perseverance rover touches down on the Red Planet on February 18, the landing will be recorded with sight, sound and maybe even touch.
      The rover will cap off a month of Mars arrivals from space agencies around the world (SN: 7/30/20). Perseverance joins Hope, the first interplanetary mission from the United Arab Emirates, which successfully entered Mars orbit on February 9; and Tianwen-1, China’s first Mars mission, which arrived on February 10 and will deploy a rover to the Martian surface in May.
      NASA will broadcast Perseverance’s landing on YouTube starting at 2:15 p.m. EST. The actual moment of touchdown is expected at approximately 3:55 p.m. EST. Perseverance is designed to explore an ancient river delta called Jezero crater, searching for signs of ancient life and collecting rocks for a future mission to return to Earth (SN: 7/28/20).
      The rover will use the landing system pioneered by its predecessor, Curiosity, which has been exploring Mars since 2012 (SN: 8/6/12). But in a first for Mars touchdowns, this rover will record its own landing with dedicated cameras and a microphone.
      As the craft carrying Perseverance zooms through the thin Martian atmosphere, three cameras will look up at the parachute slowing it down from supersonic speeds. When a rocket-powered “sky crane” platform lowers the rover to the ground, a fourth camera on the platform will record the rover’s descent. Another camera on the rover will look back up at the platform, and a sixth camera will look at the ground.
      Perseverance will use the “sky crane” landing system pioneered by its predecessor, Curiosity. The landing involves dangling the rover from a floating platform on cables and touching down directly on its wheels.JPL-Caltech/NASA
      Perseverance will use the “sky crane” landing system pioneered by its predecessor, Curiosity. The landing involves dangling the rover from a floating platform on cables and touching down directly on its wheels.JPL-Caltech/NASA
      “The goal is to see the video and the action of getting from high up in the atmosphere down to the surface,” says engineer David Gruel of NASA’s Jet Propulsion Laboratory in Pasadena, who was the engineering lead for that six-camera system, called EDL-Cam. He hopes every engineer on the team has an image of the rover hanging below the descent stage as their computer desktop background six months from now.
      Because it will take more than 11 minutes for signals to travel between Earth and Mars, the cameras won’t stream the landing movie in real time. And after Perseverance lands, engineers will be focused on making sure the rover is healthy and able to collect science data, so the landing videos won’t be among the first data sent back. Gruel expects to be able to share what the rover saw four days after landing, on February 22.

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      Perseverance will also carry microphones to record first-ever audio of a Mars landing. Unlike the landing cameras, the microphones will continue to work after touchdown, hopefully helping the engineering team keep track of the rover’s health. Motors sound different when they get clogged with dust, for instance, Gruel says. The team will hear the sound of the rover’s wheels crunching across the Martian surface, and maybe the sound of the wind blowing.
      “Are we going to hear a dust devil? What might a dust devil sound like? Could we hear rocks rolling down a hill?” Gruel asks. “You never know what we might stumble onto.”
      Sound will add a way to share Mars with people who have trouble seeing, Gruel notes. “It might appeal to a whole other element of the population who might not have been able to experience past missions the same way,” he says.
      [embedded content]
      Watch NASA’s live coverage of the Perseverance landing here starting at 2:15 p.m. EST.
      Elsewhere on Mars, the InSight lander will be listening to the landing too (SN: 2/24/20). The lander’s seismometer may be able to feel vibrations when two tungsten weights that Perseverance carried to Mars for stability smack into the ground before the rover lands, geophysicist Benjamin Fernando of the University of Oxford and colleagues report in a paper posted December 3 to eartharxiv.org and submitted to JGR Planets.
      “No one’s ever tried to do this before,” Fernando says.
      The ground will move by at most 0.1 nanometers per second, Fernando and colleagues calculated. “It’s incredibly small,” he says. “But the seismometer is also incredibly sensitive.”
      The team may be able to catch that tiny signal because they know exactly when and where the impact will happen. If the lander does pick up the signal, it will tell scientists something about how fast seismic waves travel through the ground, a clue to the details of Mars’ interior structure. And even if they don’t feel anything, that will put limits on the waves’ speed. “It still teaches us something,” Fernando says.
      The InSight team hopes to also feel vibrations from Tianwen-1 when its rover touches down in May. “Detecting one would be great,” Fernando says. “Detecting two would be like, amazing.” More

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      The number of Milky Way nova explosions per year has been pinned down

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      Each year, astronomers discover nova explosions in the Milky Way that cause dim stars to flare up and emit far more light than the sun before they fade again. But our galaxy is so big and dusty that no one knows how many of these eruptions occur throughout its vast domain, where they fling newly minted chemical elements into space.
      Now, by detecting the explosions’ infrared light, which penetrates dust better than visible light does, Caltech astronomer Kishalay De and his colleagues have estimated how often these outbursts occur in the Milky Way. Knowing the nova rate is vital for determining how much these explosions have contributed to the galaxy’s chemical makeup by creating new elements.
      The updated tally puts the rate at 46, give or take 13, a year, the team reports January 11 at arXiv.org. Past estimates of the nova rate have ranged from just 10 a year to 300.
      A nova arises from a binary star — two stars circling each other. One is a white dwarf, a dense star that’s about as small as Earth but approximately as massive as the sun. After the white dwarf receives gas from its companion, the gas explodes, making the dim star shine brilliantly. The nova does not destroy the star, unlike a supernova, which marks a star’s death.
      After observing the sky from Palomar Observatory in California for 17 months, De and colleagues detected 12 nova explosions. Estimating the number of missed outbursts, the astronomers deduced the yearly nova rate. Their rate is similar to, but more precise than, one reported four years ago by Allen Shafter, an astronomer at San Diego State University who pegged the annual nova rate at between 27 and 81.
      “They’re doing a wonderful job,” says Bradley Schaefer, an astrophysicist at Louisiana State University in Baton Rouge, who notes that searching at infrared wavelengths is ideal for finding distant explosions obscured by the galaxy’s dust. “They have an awful lot of really good data.”
      The more precise rate helps firm up estimates for how much these explosions have altered the galaxy’s chemical composition. In this regard, it’s hard for a mere nova to compete with a supernova explosion, which, though rare, releases far more newly produced elements than a nova does. But if the annual nova rate is around 50, then certain scarce isotopes on Earth — such as lithium-7, carbon-13, nitrogen-15 and oxygen-17 — arose partially or mostly in nova explosions, says Sumner Starrfield, an astronomer at Arizona State University in Tempe who was not involved with this study. The blasts then spirited these isotopes away before additional nuclear reactions could destroy them. More