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      In a first, astronomers spotted a space rock turning into a comet

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      Like the mythical half-human, half-horse creatures, centaurs in the solar system are hybrids between asteroids and comets. Now, astronomers have caught one morphing from one type of space rock to the other, potentially giving scientists an unprecedented chance to watch a comet form in real time in the decades to come.
      “We have an opportunity here to see the birth of a comet as it starts to become active,” says planetary scientist Kat Volk of the University of Arizona in Tucson.
      The object, called P/2019 LD2, was discovered by the ATLAS telescope in Hawaii in May. Its orbit suggests that it’s a centaur, a class of rocky and icy objects with unstable orbits. Because of that mixed composition and potential to move around the solar system, astronomers have long suspected that centaurs are a missing link between small icy bodies in the Kuiper Belt beyond Neptune and comets that regularly visit the inner solar system (SN: 11/19/94).
      These “short-period” comets, which are thought to originate from icy objects in the Kuiper Belt, orbit the sun once a decade or so, and make repeat appearances in Earth’s skies. (Long-period comets, like Halley’s Comet, which visits the inner solar system once a century, probably originate even farther from the sun, in the Oort cloud (SN: 10/25/13).)

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      All previously found short-period comets were spotted only after they had transitioned into comets (SN: 8/6/14). But LD2 just came in from the Kuiper Belt recently and will become a comet in as little as 43 years, Volk and colleagues report August 10 at arXiv.org.
      “It’s weird to think that this object should be becoming a comet when I’m retiring,” Volk says.
      In 2019, she and colleagues showed that there’s a region of space just beyond Jupiter that they call the “Gateway”.  In this area, small planetary objects hang out while warming up and transitioning from outer solar system ice balls to inner solar system comets with their long tails. It’s like a comet incubator, says planetary scientist Gal Sarid of the SETI Institute, who is based in Rockville, Md.
      After hearing about LD2, Volk, Sarid and their colleagues simulated thousands of possible trajectories to see where the object had been and where it is going. LD2’s orbit probably took it near Saturn around 1850, and it entered its current orbit past Jupiter after a close encounter with the gas giant in 2017, the team found. The object will leave its present orbit and move in toward the sun in 2063, where heat from the sun will probably sublimate LD2’s volatile elements, giving it a bright cometary tail, the researchers say.
      “This will be the first ever comet that we know its history, because we’ve seen it before being a comet,” Sarid says.
      The fact that LD2 is fairly new to the inner reaches of the solar system suggests that it’s made of relatively pristine material that has been in the back of the solar system’s freezer for billions of years, unaltered by heat from the sun. That would make it a time capsule of the early solar system. Studying its composition could help planetary scientists learn what the first planets were made of.
      The orbital analysis looks “very reasonable,” says Henry Hsieh, a planetary astronomer with the Planetary Science Institute who is based in Honolulu and was not involved in the study. But studying just one transition object is not enough to open the solar system time capsule.
      “What we really need to do is study many of these,” he says. “Study this one first, and then study more of them, and figure out whether this object is an outlier or whether we see a consistent picture.” Future sky surveys, like the ones planned using the future Vera Rubin Observatory (SN: 1/10/20), should discover more balls of ice shifting into comets.
      Sarid and colleagues think LD2 could be a good target for a spacecraft to visit. NASA has considered sending spacecraft to centaurs, although no missions have been selected for development yet. But considering that LD2 will become a comet in just a few decades, scientists don’t have much time to plan, build and launch a mission to visit it. “The windows are closing,” Sarid says. “We really need to be doing this now.” More

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      Hubble watched a lunar eclipse to see Earth from an alien’s perspective

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      To practice searching for extraterrestrial life, researchers have run a dress rehearsal with the one world they know to be habitable: Earth.
      While Earth was between the sun and moon for a lunar eclipse in January 2019, the Hubble Space Telescope observed how chemicals in Earth’s atmosphere blocked certain wavelengths of sunlight from reaching the moon. That observing setup mimicked the way astronomers plan to probe the atmospheres of Earthlike exoplanets as they pass in front of their stars, filtering out some starlight.
      “We basically pretend we’re alien observers looking at our planet,” says Giada Arney, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md.
      Using Hubble, the researchers focused on spotting the effects of atmospheric ozone. Because ozone is both a chemical by-product of oxygen produced in photosynthesis and a shield that protects life from the sun’s harmful ultraviolet rays, astronomers think atmospheric ozone could be a key indicator that a distant world is habitable. During the lunar eclipse, Hubble examined sunlight that had passed through Earth’s atmosphere and reflected off of the moon for signatures of ozone.

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      “It’s safer for Hubble to observe sunlight reflected off the moon” than to look directly at the backlit Earth, explains Allison Youngblood, an astronomer at the University of Colorado Boulder. The telescope’s instruments are so sensitive and Earth is so bright that “even the nightside would fry Hubble’s detectors.” 
      Those observations revealed prominent dips in particular wavelengths of ultraviolet sunlight that had been absorbed by the ozone, Youngblood, Arney and colleagues report online August 6 in the Astronomical Journal.
      The data help confirm that chemicals in the Earth’s atmosphere filter light as expected, based on researchers’ understanding of atmospheric chemistry. That finding gives astronomers more confidence that they will be able to recognize potentially habitable exoplanets. More

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      Scientists can’t agree on how clumpy the universe is

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      The universe is surprisingly smooth.
      A new measurement reveals that the universe is less clumpy than predicted, physicists report in a series of papers posted July 30 at arXiv.org. The discrepancy could hint at something amiss with scientists’ understanding of the cosmos.
      To pin down the cosmic clumpiness, researchers studied the orientation of 21 million galaxies with the Kilo-Degree Survey at the Paranal Observatory in Chile. As light from those galaxies streams through the universe, its trajectory is bent by massive objects, a phenomenon called gravitational lensing. This lensing causes the elongated shapes of galaxies to appear slightly aligned, rather than oriented randomly.
      When combined with additional data from other sky surveys, that alignment quantifies how much the matter in the universe is clumped together. The researchers found that the universe is about 10 percent more homogenous, or smoother, than predicted based on light released just after the Big Bang, the cosmic microwave background. Previous results had hinted at the discrepancy, but the new measurement strengthens the case that the disagreement is not a fluke (SN: 7/30/19).
      If the measurement is correct, the mismatch could hint at a hole in the standard model of cosmology, the theory that describes how the universe has changed over time. When combined with a similar puzzle over how fast the universe is expanding (SN: 7/15/20), physicists are beginning to suspect that the universe is putting them­­­­­ on notice.
      “It’s a bit of a riddle,” says cosmologist Hendrik Hildebrandt of Ruhr-Universität Bochum in Germany, a coauthor of the studies. “Is [the universe] just telling us ‘You’re stupid and you didn’t do your measurement right,’ or … ‘Hey, I’m more complicated than you thought’?” More

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      Jupiter’s moons could keep each other warm by raising tidal waves

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      It takes a certain amount of heat to keep an ocean wet. For Jupiter’s largest moons, a new analysis suggests a surprising source for some of that heat: each other.
      Three of the gas giant’s four largest moons, Ganymede, Callisto and Europa, are thought to harbor oceans of liquid water beneath their icy shells (SN: 5/14/18). The fourth, the volcanic moon Io, may contain an inner magma ocean (SN: 8/6/14).
      One of the primary explanations for how these small worlds stay warm enough to harbor liquid water or magma is gravitational kneading, or tidal forces, from their giant planetary host. Jupiter’s huge mass stretches and squishes the moons as they orbit, which creates friction and generates heat.
      But no studies had seriously considered how much heat the moons could get from gravitationally squishing each other.

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      “Because [the moons are] so much smaller than Jupiter, you’d think basically the tides raised by Io on Europa are just so small that they’re not even worth thinking about,” says planetary scientist Hamish Hay of NASA’s Jet Propulsion Laboratory in Pasadena, Calif.
      Together with planetary scientists Antony Trinh and Isamu Matsuyama, both of the University of Arizona in Tucson, Hay calculated the size of the tides that Jupiter’s moons would raise on each other’s oceans. The team reported the results July 19 in Geophysical Research Letters.
      The researchers found that the significance of the tides depends on how thick the ocean is. But with the right-sized ocean, neighboring moons could push and pull tidal waves on each other at the right frequency to build resonance. It’s a similar effect to pumping your legs on a swing, or synchronized footfalls making a bridge wobble, Hay says.
      “When you get into one of these resonances, those tidal waves start to get bigger,” he says. Those waves would then rush around the moon’s interior and generate heat through friction, the researchers calculated. If the conditions are right, heat from the gushing tidal waves could exceed heat from Jupiter.
      The effect was biggest between Io and Europa, the team found.
      “Basically everyone neglected these moon-moon effects,” says planetary scientist Cynthia Phillips of NASA’s Jet Propulsion Laboratory, who was not involved in the new work. “I was just astonished … at the amount of heating” that the moons may give each other, she says.
      The extra infusion of energy into Europa’s ocean could be good news for the possibility of alien life. Europa’s subsurface ocean is thought to be one of the best places in the solar system to look for extraterrestrial life (SN: 4/8/20). But anything living needs fuel, and the sun is too far away to be useful, Phillips says.
      “You have to find other sources of energy,” she says. “Any kind of frictional or heating energy is really exciting for life.” More

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      ‘Exotic’ lightning crackles across Jupiter’s cloud tops

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      Small, frequent lightning storms zip across Jupiter’s cloud tops. NASA’s Juno spacecraft spotted the flashes for the first time, scientists report August 5 in Nature.
      “It’s a very exotic thing that doesn’t exist on Earth,” says physicist Heidi Becker of NASA’s Jet Propulsion Laboratory in Pasadena, Calif.
      Previous spacecraft have revealed high-energy “superbolts” on Jupiter. That lightning originates 50 to 65 kilometers below Jupiter’s cloud tops, where liquid water droplets form. Scientists think superbolts form like lightning on Earth does: Colliding ice crystals and water droplets charge each other up, then stretch the charge between them when they separate (SN: 6/25/20).
      Juno, which arrived at Jupiter in 2016, got much closer to the giant planet’s cloud tops than previous missions. Becker and her team turned the spacecraft’s navigation camera — which normally observes stars to track Juno’s position — on Jupiter’s nightside in February 2018. To the team’s surprise, the clouds crackled with electricity.
      Newly observed lightning showed up as bright dots (indicated with arrows) on Jupiter’s nightside, seen in this composite image from two of Juno’s cameras. The insets are pixelated representations of the events’ brightness (yellow is more bright; blue is less bright).H.N. Becker et al/Nature 2020
      Superbolts are up to 100,000 times as strong as these small flashes. But the cloud-top lightning is 10 times as frequent. Strangely, the smaller bolts appeared to come from just 18 kilometers below the cloud tops, where it’s too cold for liquid water to exist alone.
      Shallow lightning must have a different origin than the deeper lightning, Becker says. Perhaps ammonia in the upper cloud decks acts as antifreeze, creating droplets of ammonia and water combined. Juno has also seen evidence that violent storms in deeper cloud layers sometimes toss ice crystals high above where they’re normally found. When those crystals collide with the ammonia-water droplets, they may charge up and create lightning, Becker and her colleagues reason.
      Similar small lightning storms may happen on other planets, including exoplanets, Becker says (SN: 5/13/16). “Every time you have a new realization, it feeds into new theories that will be developed not only for our solar system but for other solar systems.” More

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      50 years ago, Mauna Kea opened for astronomy. Controversy continues

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      Mauna Kea opened, Science News, August 1, 1970 —
      The new Mauna Kea Observatory of the University of Hawaii has been completed and dedication ceremonies have been held. Standing at an altitude of 13,780 feet on the island of Hawaii, the new observatory is the highest in the world. Its major instrument is an 88-inch reflecting telescope that cost $3 million to build.
      Update
      More than a dozen large telescopes now dot Mauna Kea, operated by a variety of organizations. Those telescopes have revolutionized astronomy, helping to reveal the accelerating expansion of the universe and evidence for the black hole at the center of the Milky Way. But the telescopes have long sparked controversy, as the dormant volcano is sacred to Native Hawaiians. Since 2014, protests have flared in response to the attempted construction of the Thirty Meter Telescope. Opponents have kept progress stalled by blocking the only access road to the site. Some scientists have spoken out against the telescope’s location. The Thirty Meter Telescope collaboration is considering the Canary Islands as a backup site. More

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      ‘The End of Everything’ explores the ways the universe could perish

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      The End of EverythingKatie MackScribner, $26
      Eventually, the universe will end. And it won’t be pretty.
      The universe is expanding at an accelerating clip, and that evolution, physicists expect, will lead the cosmos to a conclusion. Scientists don’t know quite what that end will look like, but they have plenty of ideas. In The End of Everything, theoretical astrophysicist Katie Mack provides a tour of the admittedly bleak possibilities. But far from being depressing, Mack’s account mixes a sense of reverence for the wonders of physics with an irreverent sense of humor and a disarming dose of candor.
      Some potential finales are violent: If the universe’s expansion were to reverse, the cosmos collapsing inward in a Big Crunch, extremely energetic swells of radiation would ignite the surfaces of stars, exploding them. Another version of the end is quieter but no less terrifying: The universe’s expansion could continue forever. That end, Mack writes, “like immortality, only sounds good until you really think about it.” Endless expansion would beget a state known as “heat death” — a barren universe that has reached a uniform temperature throughout (SN: 10/2/09). Stars will have burned out, and black holes will have evaporated until no organized structures exist. Nothing meaningful will happen anymore because energy can no longer flow from one place to another. In such a universe, time ceases to have meaning.
      Perhaps more merciful than the purgatory of heat death is the possibility of a Big Rip, in which the universe’s expansion accelerates faster and faster, until stars and planets are torn apart, molecules are shredded and the very fabric of space is ripped apart.

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      These potential endings are all many billions of years into the future — or perhaps much further off. But there’s also the possibility that the universe could end abruptly at any moment. That demise would not be a result of expansion or contraction, but due to a phenomenon called vacuum decay. If the universe turns out to be fundamentally unstable, a tiny bubble of the cosmos could convert to a more stable state. Then, the edge of that bubble would expand across the cosmos at the speed of light, obliterating anything in its path with no warning. In a passage a bit reminiscent of a Kurt Vonnegut story, Mack writes, “Maybe it’s for the best that you don’t see it coming.”
      Already known for her engaging Twitter personality, public lectures and popular science writing, Mack has well-honed scientific communication chops. Her evocative writing about some of the most violent processes in the universe, mixed with her obvious glee at the unfathomable grandness of it all, should both satisfy longtime physics fans and inspire younger generations of physicists.
      Reading Mack’s prose feels like learning physics from a brilliant, quirky friend. The book is sprinkled with plenty of informal quips: “I’m not going to sugarcoat this. The universe is frickin’ weird.” Readers will find themselves good-naturedly rolling their eyes at some of the goofy footnotes and nerdy pop-culture references. At the same time, the book delves deep into gritty physics details, thoroughly explaining important concepts like the cosmic microwave background — the oldest light in the universe — and tackling esoteric topics in theoretical physics. Throughout, Mack does an excellent job of recognizing where points of confusion might trip up a reader and offers clarity instead.
      Mack continues a long-standing tradition of playfulness among physicists. That’s how we got stuck with somewhat cheesy names for certain fundamental particles, such as “charm” and “strange” quarks, for example. But she also brings an emotional openness that is uncommon among scientists. Sometimes this is conveyed by declarations in all caps about how amazing the universe is. But other times, it comes when Mack makes herself vulnerable by leveling with the reader about how unnerving this topic is: “I’m trying not to get hung up on it … the end of this great experiment of existence. It’s the journey, I repeat to myself. It’s the journey.”
      Yes, this is a dark subject. Yes, the universe will end, and everything that has ever happened, from the tiniest of human kindnesses to the grandest of cosmic explosions, will one day be erased from the record. Mack struggles with what the inevitable demise of everything means for humankind. By contemplating the end times, we can refine our understanding of the universe, but we can’t change its fate.
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