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    How tiny red stars can test ideas about the origin of life

    A survey of small, cool stars is helping to narrow in on the conditions that might set the stage for life beyond our solar system.

    A look at about 200 ultracool dwarf stars shows that they lack sufficient ultraviolet light intensity to have the potential to jump-start life, researchers report December 1 in the Monthly Notices of the Royal Astronomical Society. That may initially seem to be bad news for finding signs of alien life on distant planets. But the diminutive stars could instead serve as test beds to determine what other conditions can create the chemical foundations of life.

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    Compared with our sun, the dwarf stars in the new study are minuscule, roughly the size of Jupiter and weighing about a tenth as much as the sun. They’re also among the most common types of stars. And because they’re cool and comparatively dim, it’s often easier to spot planets orbiting them than it is in the glare of large bright stars. Astronomers studying the tiny red star TRAPPIST-1, for example, found that it hosts seven Earth-sized planets, including three that may be within the star’s habitable zone, where conditions are amenable to life (SN: 2/22/17).

    For life to exist on a habitable planet, though, it must start somehow. One possibility is that UV starlight provides the energy needed to link together the hydrogen, oxygen, carbon, nitrogen, sulfur and other atoms that make up the compounds that are precursors to life.

    With that in mind, space scientist Antígona Segura and colleagues used the Transiting Exoplanet Survey Satellite to measure the amount of UV radiation — among other things — emitted from 208 comparatively nearby ultracool dwarfs within 130 light-years from Earth (SN: 4/12/18). The stars they studied do emit UV light, as our sun does, and many produce bursts of UV when they let off flares. But overall, the UV energy the small stars release is too low to forge the chemicals needed to kick-start life, the team found.

    The dearth of UV light doesn’t necessarily quash hopes of finding life around such stars. “UV is an energy source for prebiotic chemistry that we can measure, and that is why we focused on it,” says Segura, of the National Autonomous University of Mexico in Mexico City. “But there are many other energy sources, like cosmic and stellar particles, and particles, radiation and heat produced by radioactive decay, to name a few.”

    Ultracool stars might be useful to discover whether something other than UV light can get life going. “We should search for life on the planets that have the least [UV] activity, where we can know with confidence that UV-driven prebiotic chemistry cannot happen,” says Paul Rimmer, a University of Cambridge astrophysicist who was not involved in the study. “If we find evidence of life on these [types of] planets, this will show that there are other paths to life.”

    Also, Segura notes, sources of energy that could start life can also make planets less habitable for more complex life-forms. “We cannot currently say which [effects] would prevail. The best approach now is to study case by case and wait for more observational constraints, like for the case of the TRAPPIST-1 system.”

    If astronomers eventually find life on planets orbiting ultracool dwarfs, it will confirm the potential for UV-free origins of life. But, Rimmer says, if it turns out that there are no signs of habitability on planets around the many small, dim dwarf stars we see, that would lower estimates of the likelihood of finding life outside our solar system. Either way, future surveys of ultracool dwarf stars could give researchers a better handle on the possible prevalence of extraterrestrial life in the universe. More

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    Giant polygon rock patterns may be buried deep below Mars’ surface

    Enormous polygon patterns in rock lie dozens of meters below Mars’ surface, ground-penetrating radar data suggest.

    Similar patterns develop on the surface in Earth’s polar regions when icy sediments cool and contract. A comparable process long ago may have created the shapes on Mars, found near the planet’s dry equator, researchers report November 23 in Nature Astronomy.

    If so, the finding hints that the Red Planet’s equator was much wetter and icier, more like a polar region, when the polygons formed 2 billion to 3 billion years ago.

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    “Buried possible polygons at that depth have yet to be reported” on Mars, says planetary scientist Richard Soare of Dawson College in Montreal, who was not involved in the study. Searching for ancient polygonal terrain on Mars using ground-penetrating radar is a new idea that “could be powerful,” he adds, and could help scientists understand how Mars’ climate has changed in the past.

    On Earth, polygonal terrain forms in chilly climes when sharp temperature drops cause icy ground to contract and crack open. These thermal fractures are small at first. But the little cracks can fill with ice, sand, or a bit of both, forming “wedges” that prevent the cracks from healing and gradually pry open the earth as they grow. Because this wedging process requires multiple cycles of freezing and thawing, polygonal ground is a good hint that the terrain was icy when the patterns formed.

    Polygonal surface patterns on Mars — like these in western Utopia Planitia, glimpsed from orbit by the Mars Global Surveyor satellite —might have been carved by “ice wedges” that form over many cycles of freezing and thawing.JPL/NASA, Malin Space Science Systems

    But the Chinese Zhurong rover’s landing site, on a part of Mars called Utopia Planitia, is not the kind of place one would expect to find the terrain on Earth — at least not today (SN: 5/19/21). Polygons have been spotted at higher latitudes on the Martian surface from orbit, but the landing site sits near the Martian equator in a dry, sandy dune field (SN: 8/24/04).

    The polygons appear to be roughly 70 meters across and are bordered by wedges nearly 30 meters wide and tens of meters deep — about 10 times as large as typical polygons and wedges on Earth. So it’s possible, Soare says, the structures here formed a bit differently than ice-wedge polygons on Earth.Forming polygons near the Martian equator wouldn’t be possible today, says study coauthor Ross Mitchell, a geoscientist also at the Institute of Geology and Geophysics. To form polygons, the region must have been colder and wetter in the past, he says — much like a polar region.

    Changes in the tilt of Mars’ axis could explain such a shift in climate. Simulations of Mars’ orbit have suggested that the planet’s spin axis has at times been so extremely tilted that the planet essentially lay halfway on its side. This would cause the poles to receive more direct sunlight while equatorial regions froze. Finding potential polygons buried near the Martian equator, Mitchell says, is “smoking gun evidence” supporting the idea that the tilt of Mars’ axis has varied so substantially in the past.

    “We think of every planet other than Earth as dead,” Mitchell says. But if Mars’s axis does swing around often, he says, our neighboring planet’s climate would be far more dynamic than currently believed. More

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    A rare, extremely energetic cosmic ray has mysterious origins

    The “Oh-My-God” particle has a new companion.

    In 1991, physicists spotted a particle from space that crashed into Earth with so much energy that it warranted an “OMG!” With 320 quintillion electron volts, or exaelectron volts, it had the kinetic energy of a baseball zipping along at about 100 kilometers per hour.

    Now, a new particle of comparable energy has been found, researchers report in the Nov. 24 Science. Detected in 2021 by the Telescope Array experiment near Delta, Utah, the particle had an energy of about 240 exaelectron volts. And mysteriously, scientists are unable to pinpoint any cosmic source for the particle.

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    “It’s a huge, huge amount of energy but in a tiny, tiny, tiny object,” says astroparticle physicist John Matthews of the University of Utah in Salt Lake City, co-spokesperson of the Telescope Array collaboration.

    Cosmic rays consist of protons and atomic nuclei that zip through space at wide range of energies. Particles with energies over 100 exaelectron volts are exceedingly rare: On average, scientists estimate, one such particle falls on a square kilometer of Earth’s surface each century. And particles over 200 exaelectron volts are even rarer — only a few such particles have previously been detected.

    When a cosmic ray hits Earth, it collides with a nucleus of an atom in the atmosphere, creating a cascade of other particles that can be detected on Earth’s surface.

    To catch the rarest, highest-energy particles, scientists build giant arrays of detectors. The Telescope Array monitors an area of 700 square kilometers using more than 500 detectors made of plastic scintillator, material that emits light when hit by a charged particle. Additional detectors measure ultraviolet light produced in the sky by the shower of particles (although those detectors weren’t operating during the newly reported particle’s arrival). Based on the times that individual scintillator detectors were hit by the cascade of particles, scientists can determine the direction of the incoming cosmic ray and use that information to trace it back to its origins.

    Extremely high-energy cosmic rays come from outside the Milky Way, but their exact sources are unknown (SN: 9/21/17). Most scientists think they are accelerated in violent cosmic environments, such as the jets of radiation that blast out of the areas around certain supermassive black holes, or starburst galaxies that form stars at a frenetic pace. 

    Whatever their origins, the particles must come from the relatively nearby cosmic neighborhood. That’s because the highest-energy cosmic rays lose energy as they travel, by interacting with the cosmic microwave background, the afterglow of the Big Bang (SN: 7/24/18).

    Tracing back the particle’s location is complicated. “The issue is that when you detect a high-energy cosmic ray at Earth, the arrival direction that you get will not point to the source because it will be deflected by … any magnetic field that would be in the way,” says Telescope Array collaborator Noémie Globus, an astroparticle physicist at the University of California, Santa Cruz and the RIKEN research institute in Japan.  

    The magnetic fields present in the Milky Way and its environs scatter the cosmic rays like fog scatters light. To trace the particle to its home, scientists must take that scattering into account. But that backtracking pinpointed a cosmic void, a region of space with few galaxies at all, much less ones with violent processes going on. 

    That makes this particle particularly interesting, says astrophysicist Vasiliki Pavlidou of the University of Crete in Heraklion, Greece. “It’s actually pointing towards nothing at all, absolutely in the middle of nowhere.”

    That might hint that scientist are missing something. For example, researchers may need to better understand the magnetic fields of the galaxy, says Pavlidou, who was not involved with the research. 

    “Every time you have one of these very high-energy events, just because they are so rare, it’s a big deal.” More

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    A rare glimpse at a relatively nearby supernova offers clues to how stars die

    In May, a star in the Pinwheel galaxy exploded in just the right place at nearly the right time for astronomers to unravel details of its death. It was the closest supernova to go off in the last five years.

    Astronomers have long been fascinated with these stellar explosions, which signal the end of life for the universe’s biggest stars. Not only are they dramatic — a supernova can shine 5 billion times as bright as our sun — but the explosions seed the universe with gold, silver, zinc and other elements forged only in a dying star’s last moments.

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    Giant planet ‘destabilization’ may have coincided with the birth of Earth’s moon

    A long-ago reshuffling of the giant planets in our solar system may have been instrumental in giving Earth its moon.

    For decades, planetary scientists have hypothesized that Jupiter, Saturn, Uranus and Neptune were born much closer to the sun and that gravitational interactions among those planets jolted them into their contemporary trajectories (SN: 5/10/22). But the timing of that “giant planet orbital instability” has been tricky to nail down.

    Now, an analysis of meteorite data suggests that the instability took place between 60 million and 100 million years after the solar system started forming, planetary scientist Alessandro Morbidelli reported October 5 in San Antonio at a meeting of the American Astronomical Society’s Division for Planetary Sciences. That timing also roughly coincides with when Earth’s moon is thought to have formed in the wake of a Mars-sized planet running into our own.

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    The instability of the giant planets “is related to a complete reshaping of the solar system, the formation of the cometary reservoirs, the sculpting of the asteroid belt,” says Morbidelli, of the Observatoire de la Côte d’Azur in Nice, France. “Understanding when it occurred means fixing a milestone in the history of the solar system.”

    The giant planet migration, first proposed by Morbidelli and colleagues in 2005, is a widely accepted hypothesis for explaining much about the solar system. In particular, the giant planets travel along slightly elongated orbits that are askew to one another. But observations of other planetary systems and computer simulations of planet formation suggest that giant planets, in general, form on closer-in orbits that are circular and coplanar. Using simulations, Morbidelli and others showed that if the giant planets in our solar system formed like that, they wouldn’t stay that way. Gravitational interactions would eventually knock the planets into the orbits they have today.

    At first, the team thought this instability occurred about 600 million years after the birth of the solar system. That timing meant the migration of the giant planets could also explain an apparent asteroid bombardment of the terrestrial planets — Mercury, Venus, Earth and Mars — as evidenced by craters on the moon and lunar rocks brought back by Apollo astronauts. More recent work, however, has cast doubt on the reality of this “lunar cataclysm.”

    Now, Morbidelli suspects the orbital instability came a lot earlier. His reasoning starts with a rare type of meteorite called EL enstatite chondrites.

    The mix of elements in these meteorites suggests they must be the remnants of a large rocky body, a few hundred kilometers across, born near the terrestrial planets in the dusty disk that once swirled around our sun.

    Then, in 2022, Morbidelli and colleagues showed that any of these enstatites that land on Earth today must come from a collection of bits and pieces in the asteroid belt between Mars and Jupiter. Those bits all broke off Athor, one of the many asteroids there, after it collided long ago with some other object in the belt. Altogether, that family of material adds up to an asteroid roughly 60 kilometers across — much smaller than the one thought to have birthed the enstatites in the first place. That means Athor must be only one piece of that larger rocky body, left over from a collision that destroyed it much closer to the sun.

    “The question is, which dynamical mechanism can allow the implantation of Athor in the asteroid belt?” Morbidelli said at the meeting.

    He tried computer simulations of several possibilities, but so far, only the giant planet instability seems capable of sending Athor to a stable orbit in the asteroid belt.

    This couldn’t have happened earlier than 60 million years after the birth of the solar system, Morbidelli said. Radioactive elements in the enstatite chondrites indicate their parent body was slowly cooling until then, which means it was still large. It hadn’t yet collided with one of the many other planetesimals stirred around by the forming terrestrial planets.

    On the other hand, simulations suggest the instability can’t have occurred later than about 100 million years after the solar system began. A study in 2018 concluded that if the giant planets migrated later, a pair of asteroids dubbed Patroclus-Menoetius, trailing Jupiter around the sun while orbiting each other, would have been pulled apart.

    That 60-million- to 100-million-year window makes the instability a prime suspect in the diversion of a hypothesized planet that hit Earth, creating the moon (SN: 3/15/23).  The timing “seems right,” says Matthew Clement, an astrophysicist at the Johns Hopkins Applied Physics Laboratory in Laurel, Md.  “Lots of things were happening in the solar system’s early history. However, dynamically speaking, we don’t have a whole lot of reason to believe that things changed much after the moon-forming impact.”

    But he cautions that Morbidelli’s estimate is based on “one data point, of the breakup of one asteroid, pieces of which serendipitously happened to get to Earth.”

    Still, “it’s nice that [the new result] is actually based on some real data, even if it’s indirectly, rather than just computer models,” says planetary scientist John Chambers. He has questions, though. “They suggest this happened when the formation of the terrestrial planets was more or less complete, apart maybe from the giant impact that formed the moon,” says Chambers, of the Carnegie Institution for Science in Washington, D.C. “But then there’s a good chance it would have messed up the orbits of the terrestrial planets and possibly led to some of them colliding,” which the current lineup of planets suggests did not happen.

    Both Chambers and Matthews have worked on scenarios in which the orbital instability occurred even earlier, just a few million years after the solar system began. That earlier time for the instability would help explain one of the outstanding riddles of the solar system: the relatively small size of Mars compared with Earth and Venus. That’s because the instability would have removed many objects from near the orbit of Mars before it could grow to the size of Earth or larger. The new result from Morbidelli’s team seems to exclude that solution.

    “I’m prepared to rely on the evidence,” Chambers says. But he isn’t convinced yet because many facets of the solar system’s present structure must be reconciled with any date for the giant planet instability.

    Clement agrees. “There’s problems if the instability happened at 500 million years. There’s still problems that we have to resolve if it happened when they say it happened,” he says. “And there’s still problems if it happened immediately after the planets formed, in the first few million years. This story is not done being told yet.” More

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    Here’s another strike against Venus having copious lightning

    Venus has long been depicted as having a hellish atmosphere. Despite that reputation, evidence increasingly suggests that our neighbor’s cloudy shroud isn’t riddled with lightning.

    Last month, planetary scientists proposed that most if not all of the bright flashes observed in Venus’ atmosphere could be explained by meteors (SN: 9/11/23). Now, a separate team suggests that whistling electromagnetic waves often created by lightning on Earth and other planets are not sparked by lightning on Venus.

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    In 2021, the Parker Solar Probe swung past the nighttime side of Venus on its way toward the sun (SN: 12/15/21). As it did, its instruments picked up radio waves that scientists have dubbed whistler waves. Such disturbances got their name because their frequency quickly changes from high to low before they disappear, says Harriet George, a space physicist at the University of Colorado Boulder.

    Oddly, Venus’ whistler waves were traveling downward toward the planet, not up and away from it, as they would have been if they’d been caused by lightning, George and her team report in the Oct. 16 Geophysical Research Letters.

    An alternate source of energy for these whistler waves could be disturbances in Venus’ weak magnetic fields, the researchers suggest. As magnetic field lines shift and reconnect, they can release prodigious amounts of energy, George says. In other milieus, magnetic reconnections accelerate the solar wind, help heat the sun’s outer atmosphere and help trigger Earth’s auroras (SN: 6/7/23; SN: 11/14/19; SN: 7/24/08). They’ve got the right characteristics to create whistler waves on Venus too. More

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    The black hole–powered jet in galaxy M87 is making stars explode

    High-speed gas shooting from the galaxy M87 is causing stars to go nova, a study suggests, and no one knows how.

    A nova occurs after a dense star known as a white dwarf receives gas from an orbiting star (SN: 2/12/21). As the white dwarf’s intense gravity squeezes the gas, it heats up and explodes, but both stars survive the violence. In fact, over millions of years, the same star goes nova again and again. Recent observations indicate that these eruptions forged much, and perhaps most, of the universe’s supply of the valuable metal lithium (SN: 5/7/19).

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    Nova explosions erupt in our galaxy as well as others, including the giant elliptical M87, whose jet of fast-moving gas is powered by the black hole at the galaxy’s center (SN: 4/10/19). Now Hubble Space Telescope data show that there’s an excess of these explosions along M87’s jet, researchers report in a study submitted September 28 to arXiv.org.

    Alec Lessing, an undergraduate student at Stanford University, Michael Shara, an astronomer at the American Museum of Natural History in New York City, and their colleagues used the telescope to locate 135 nova outbursts in M87, whose jet is many thousands of light-years long. The galaxy itself is 54 million light-years from Earth, at the heart of the nearest galaxy cluster, named Virgo.

    The Hubble Space Telescope snapped this composite picture of the galaxy M87 and its jet of fast-moving gas, which is many thousands of light-years long.NASA, The Hubble Heritage Team/STScI/AURA

    After identifying the nova explosions, the team plotted their positions in the galaxy. “It was striking to the eye,” Shara says of the plot. “The novae appeared to be preferentially aligned with the jet.”

    By dividing the galaxy into 10 equal sectors, the astronomers found that 25 blasts occurred along the jet — versus only 10 to 16 in each of the galaxy’s other sectors. The chance that this is just a statistical fluke is only about 0.3 percent, the researchers say.

    “I was really surprised,” says Massimo Della Valle, an astronomer at the Italian National Institute for Astrophysics in Naples, who was not involved with the new study. “If these objects are novae, the jet has to be responsible for this somehow.”

    Perhaps, he says, the jet pushes interstellar gas onto white dwarf stars in nova systems, increasing the amount of material that accumulates on the stars’ surfaces. As a result, the white dwarfs explode more frequently than they otherwise would, accounting for the surplus of nova outbursts along the jet.

    The jet itself, Shara says, doesn’t seem to supply enough gas or radiation to explain the explosions. “The jet is to blame, but we just don’t know why or how,” he says. “It is somehow causing the novae to be more prevalent in that sector, but whether it’s because it’s triggering the novae somehow or birthing the novae — making more of them there — or some other process … we don’t know.”

    For additional clues, Shara hopes to use Hubble to examine other galaxies that resemble M87, to see whether their jets are also accompanied by such eruptions. More

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    In a first, astronomers spot the afterglow of an exoplanet collision

    In a solar system about 1,800 light-years from Earth, two planets smacked into one another in an impact that vaporized them both. And astronomers caught them in the act.

    An incandescent blob of leftover planet, lingering after an impact, could explain a surge of infrared light from a remote star, researchers report October 11 in Nature. And the ensuing debris field could also explain a subsequent dimming of the star, the team says. While scientists have glimpsed planetary debris in other solar systems before, no one has seen the smoldering remains of a collision between exoplanets until now (SN: 5/8/23).

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    “The possible detection of a post-impact body is really exciting,” says astrophysicist Philip Carter of the University of Bristol in England, who was not involved in the new study. “As far as I’m aware, no one’s claimed this before.”

    As is often the case for exciting astronomical discoveries, detecting the aftermath of this cosmic smackdown involved more than a little luck.

    Astronomer Matthew Kenworthy wasn’t hunting for giant impacts. “I was looking for rings” around exoplanets, he says (SN: 2/1/15). So he was scouring telescope survey data for stars that flicker or dim in unusual ways. And when the ASAS-SN survey — an ongoing project to monitor the entire sky for exploding stars — captured the sunlike star ASASSN-21qj repeatedly dimming in visible light, “I immediately jumped on it,” says Kenworthy, of Leiden Observatory in the Netherlands.

    As he was analyzing the fading star, Kenworthy stumbled upon another clue — on social media. One of his posts on Twitter (now called X) about ASASSN-21qj’s unusual behavior caught the eye of citizen scientist Arttu Sainio. “I tweeted out saying: ‘Oh, this is amazing, this star is fading!’” Kenworthy says. “Then he said: ‘Oh, by the way, did you realize the star had brightened up [in infrared]?’”

    Sainio pointed out that infrared data from NASA’s orbiting WISE telescope showed a strong uptick in infrared radiation from the star about 900 days before the dimming started. Kenworthy’s hopes for rings were dashed. But maybe he and his colleagues had found something else just as fascinating.

    “It just totally changed the story,” Kenworthy says.

    The researchers realized that a giant impact could neatly tie together the spontaneous infrared glow and the visible light dimming that followed more than two years later. Their calculations suggest that two Neptune-sized planets collided, vaporizing each other and forming a hot, donut-shaped body of vaporized rock — the source of the infrared glow. ASASSN-21qj later dimmed when impact debris smeared out around the star and blocked some of its light.

    [embedded content]
    Two exoplanets collided in a smashup that left behind a glob of hot, vaporized rock and a debris cloud. Astronomers first observed the afterglow of the collision in infrared light. Then, 900 days later, they saw the pulverized planets’ star dim as impact debris drifted in front of it, between the star and Earth.

    Alternatively, it’s possible that astronomers observed two separate events: an infrared glow from dust warmed by starlight, perhaps left behind by a collision between close-orbiting protoplanets, followed by dimming as a big disk of unrelated material passed in front of the star. But two rare events happening in close succession is “really, really, really unlikely,” Kenworthy says.

    The putative post-impact blob could one day coalesce into a planet. And as the remaining debris shears out into a disk orbiting the star, it too might eventually collect onto the new planet or form moons around it.

    How long all that might take isn’t clear, Carter says. It could happen within a few years or perhaps several thousand. “The models of these impact remnants are still in the very early stages,” he says. Either way, continuing to observe the post-impact material over the coming years will give scientists a rare chance to witness, not just simulate, what happens after a planetary collision.

    “You expect astronomical processes to take astronomical amounts of time. And it’s like: Nope! This was very fast. This happened over just a few years,” Kenworthy says. “It’ll just be fascinating to see how it evolves over time, in the next 10 or 20 years.” More