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    A shadowy birthplace may explain Jupiter’s strange chemistry

    Jupiter may have formed in a shadow that kept the planet’s birthplace colder than Pluto. The frigid temperature could explain the giant world’s unusual abundance of certain gases, a new study suggests.

    Jupiter consists mostly of hydrogen and helium, which were the most common elements in the planet-spawning disk that spun around the newborn sun. Other elements that were gases near Jupiter’s birthplace became part of the planet, too, but in only the same proportions as they existed in the protoplanetary disk (SN: 6/12/17).

    Astronomers think the sun’s composition of elements largely reflects that of the protoplanetary disk, so Jupiter’s should resemble that solar makeup — at least for elements that were gases. But nitrogen, argon, krypton and xenon are about three times as common on Jupiter, relative to hydrogen, as they are on the sun.

    “This is the main puzzle of Jupiter’s atmosphere,” says Kazumasa Ohno, a planetary scientist at the University of California, Santa Cruz. Where did those extra elements come from?

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    If Jupiter was born at its current distance from the sun, the temperature of the planet’s birthplace would have been around 60 kelvins, or –213˚ Celsius. In the protoplanetary disk, those elements should be gases at that temperature. But they would freeze solid below about 30 kelvins, or –243˚ C. It’s easier for a planet to accrete solids than gases. So if Jupiter somehow arose in a much colder environment than its current home, the planet could have acquired solid objects laden with those extra elements as ice.

    For this reason, in 2019 two different research teams independently made the radical suggestion that Jupiter had originated in the deep freeze beyond the current orbits of Neptune and Pluto, then spiraled inward toward the sun.

    Now Ohno and astronomer Takahiro Ueda of the National Astronomical Observatory of Japan propose a different idea: Jupiter formed where it is, but a pileup of dust in between the planet’s orbit and the sun blocked sunlight, casting a long shadow that cooled Jupiter’s birthplace. The frosty temperature made nitrogen, argon, krypton and xenon freeze solid and become a greater part of the planet, the scientists suggest in a study in the July Astronomy & Astrophysics.

    The dust that cast the shadow came from rocky objects closer to the sun that collided and shattered. Farther from the sun, where the protoplanetary disk was colder, water froze, giving rise to objects that resembled snowballs. When those snowballs collided, they were more likely to stick together than shatter and thus didn’t cast much of a shadow, the researchers say.

    “I think it’s a clever fix of something that might have been difficult to rectify otherwise,” says Alex Cridland, an astrophysicist at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany.

    Cridland was one of the scientists who had suggested that Jupiter formed beyond Neptune and Pluto. But that theory, he says, means Jupiter had to move much closer to the sun after birth. The new scenario avoids that complication.

    Measuring the atmospheric composition of Saturn may pinpoint the birthplace of Jupiter.NASA, ESA, A. Simon/GSFC, M.H. Wong/UCB, the OPAL Team

    How to test the new idea? “Saturn might hold the key,” Ohno says. Saturn is nearly twice as far from the sun as Jupiter is, and the scientists calculate that the dust shadow that chilled Jupiter’s birthplace barely reached Saturn’s. If so, that means Saturn arose in a warmer region and so should not have acquired nitrogen, argon, krypton or xenon ice. In contrast, if the two gas giants really formed in the cold beyond the present orbits of Neptune and Pluto, then Saturn should have lots of those elements, like Jupiter.

    Thanks to the Galileo probe, which dove into the Jovian atmosphere in 1995, astronomers know these abundances for Jupiter. What’s needed, the researchers say, is a similar mission to Saturn. Unfortunately, while orbiting Saturn, the Cassini spacecraft (SN: 8/23/17) measured only an uncertain level of nitrogen in the Ringed Planet’s atmosphere and detected no argon, krypton or xenon, so Saturn doesn’t yet constrain where the two gas giants arose.     More

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    Richard Lewontin: Pioneering evolutionary biologist dies aged 92

    By New Scientist

    Museum of Comparative Zoology, Harvard
    Richard Lewontin, the geneticist and evolutionary biologist whose research showed that humans from different ethnic backgrounds aren’t as genetically different as appearances might suggest, has died at the age of 92.
    Lewontin’s work revealed that nearly 85 per cent of humanity’s genetic diversity is seen between individuals of a single population, such as those of a single nation. A further 8 per cent occurs between such populations that might have been put into the same racial category. Differences between ethnic groups accounted for just 7 per cent of genetic diversity. Simply put: two people are different because they are … More

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    First farmers in the Atacama Desert had a history of brutal violence

    By James Urquhart

    An aerial view of coastal area of Llanos de Challe National Park in the Atacama Desertabriendomundo/Getty Images
    When coastal hunter-gatherers settled inland to begin farming about 3000 years ago in the Atacama desert, their violence became more gruesome, often with intent to kill, according to a study of human remains from the time.
    Vivian Standen at the University of Tarapacá in Chile and her colleagues studied signs of violence in the remains of 194 adults buried between 2800 and 1400 years ago in a coastal desert valley of northern Chile.
    The team … More

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    in Space & Astronomy

    Scientists spotted an electron-capture supernova for the first time

    A long-predicted type of cosmic explosion has finally burst onto the scene.

    Researchers have found convincing evidence for an electron-capture supernova, a stellar explosion ignited when atomic nuclei sop up electrons within a star’s core. The phenomenon was first predicted in 1980, but scientists have never been sure that they have seen one. A flare that appeared in the sky in 2018, called supernova 2018zd, matches several expected hallmarks of the blasts, scientists report June 28 in Nature Astronomy.

    “These have been theorized for so long, and it’s really nice that we’ve actually seen one now,” says astrophysicist Carolyn Doherty of Konkoly Observatory in Budapest, who was not involved with the research.

    Electron-capture supernovas result from stars that sit right on the precipice of exploding. Stars with more than about 10 times the sun’s mass go supernova after nuclear fusion reactions within the core cease, and the star can no longer support itself against gravity. The core collapses inward and then rebounds, causing the star’s outer layers to explode outward (SN: 2/8/17). Smaller stars, with less than about eight solar masses, are able to resist collapse, instead forming a dense object called a white dwarf (SN: 6/30/21). But between about eight and 10 solar masses, there’s a poorly understood middle ground for stars. For some stars that fall in that range, scientists have long suspected that electron-capture supernovas should occur.

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    During this type of explosion, neon and magnesium nuclei within a star’s core capture electrons. In this reaction, an electron vanishes as a proton converts to a neutron, and the nucleus morphs into another element. That electron capture spells bad news for the star in its war against gravity because those electrons are helping the star fight collapse.

    According to quantum physics, when electrons are packed closely together, they start moving faster. Those zippy electrons exert a pressure that opposes the inward pull of gravity. But if reactions within a star chip away at the number of electrons, that support weakens. If the star’s core gives way — boom — that sets off an electron-capture supernova.

    But without an observation of such a blast, it remained theoretical. “The big question here was, ‘Does this kind of supernova even exist?’” says astrophysicist Daichi Hiramatsu of the University of California, Santa Barbara and Las Cumbres Observatory in Goleta, Calif. Potential electron-capture supernovas have been reported before, but the evidence wasn’t definitive.

    So Hiramatsu and colleagues created a list of six criteria that an electron-capture supernova should meet. For example, the explosions should be less energetic, and should forge different varieties of chemical elements, than more typical supernovas. Supernova 2018zd checked all the boxes.

    A stroke of luck helped the team clinch the case. Most of the time, when scientists spot a supernova, they have little information about the star that produced it — by time they see the explosion, the star has already been blown to bits. But in this case, the star showed up in previous images taken by NASA’s Hubble Space Telescope and Spitzer Space Telescope. Its properties matched those expected for the type of star that would produce an electron-capture supernova.

    “All together, it really is very promising,” says astrophysicist Pilar Gil-Pons of Universitat Politècnica de Catalunya in Barcelona. Reading the researchers’ results, she says, “I got pretty excited, especially about the identification of the progenitor.” 

    Finding more of these supernovas could help unveil their progenitors, misfit stars in that odd mass middle ground. It could also help scientists better nail down the divide between stars that will and won’t explode. And the observations could reveal how often these unusual supernovas occur, an important bit of information for better understanding how supernovas seed the cosmos with chemical elements. More

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    A Psalm for the Wild-Built by Becky Chambers is joyful sci-fi reading

    The relationship between a robot and a monk is at the heart of a new bookZoonar GmbH/Alamy
    A Psalm for the Wild-Built
    Becky Chambers
    Tor.comAdvertisement

    I READ a lot of sci-fi and, my, the future can be grim at times. Whether it is characters dealing with alien invasions, technology gone wrong or the ravages of climate change, most modern books in the genre are dour affairs, in stark contrast to the “golden age” sci-fi of the 1940s and 50s, when unrealistic techno-utopianism ruled.
    But it isn’t all bad. Increasingly, authors are writing “hopepunk” stories (a slightly cringeworthy term inspired by cyberpunk) that weaponise optimism, according to one Vox journalist.
    At the forefront of this subgenre is Becky Chambers, award-winning author of the Wayfarers series. But unlike the golden age stories, Chambers’s characters live complex lives and know that not all problems can be tackled with the wave of a plot-solving gizmo. Instead, they rely on relationships to succeed, picking each other up and dusting themselves down in the face of adversity.
    The Long Way to a Small, Angry Planet, the first book in the series, details the adventures of the crew of the ship Wayfarer. As the title suggests, it is much more about the journey than the destination. In a way, not a lot happens, but all the characters are changed by their interactions with one another.
    My favourite character in the book is the charming and tragic Dr Chef (yes, he is the ship’s doctor and chef), one of the last of an alien species called Grum, which resemble a kind of six-limbed otter and gradually change biological sex over their lifetime.
    This is just one example of the incredibly diverse cast of aliens that populate the Wayfarers books, which share a universe but mostly stand alone. There are Aeluons, who communicate by flashing colours on their faces, and the reptilian Aandrisk, whose society is influenced by the fact they lay eggs – children are normally the result of casual sex, and aren’t reared by their biological parents.
    There are also artificial intelligences that run ships and other hardware, but it is illegal to upload an AI to a humanoid robot. This is key in the second book, A Closed and Common Orbit, which is a fantastic examination of identity and autonomy.
    Chambers’s latest, the novella A Psalm for the Wild-Built, takes place in a new continuity outside the Wayfarers universe, but shares much of its DNA. It is set on a moon called Panga where humans realised that their sprawling, oil-burning factories were unsustainable and set up a vast rewilding project. “It was a crazy split, if you thought about it: half the land for a single species, half for the hundreds of thousands of others,” writes Chambers. “Finding a limit they’d stick to was victory enough.” Around the same time, robots became sentient and withdrew to the new wilderness, with humans promising to leave them alone.
    The book is set some time after this Transition, and follows a tea monk, Sibling Dex, who goes from settlement to settlement as a travelling salesperson-slash-roaming therapist. Despite bringing joy and comfort to those visited, Dex is unsatisfied and heads out into the wilds, looking for a new purpose – eventually making contact with a robot, Mosscap, the first time humans and robots had met in centuries.
    The heart of the book is the relationship between the two and the way they support each other. It is a joyful experience and, as with all of Chambers’s books, I was left with a warm, fuzzy feeling inside.

    Jacob also recommends…
    TV
    Legends of Tomorrow
    This show about time-travelling superheroes embraces the joy of being silly, and it is now one of my favourites. A recent episode has them meet David Bowie in 1970s London and find Spartacus on a spaceship.
    Book
    Revenger
    Alistair Reynolds
    The first novel in a trilogy sees sisters Adrana and Fura Ness join the crew of the Revenger, led by the space pirate Captain Rackamore, for swashbuckling sci-fi.

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    Don't Miss: Biohackers returns to Netflix for season 2

    Netflix
    Watch
    Biohackers returns to Netflix for a second season, following a group of students at a German university caught up in the moral and ethical issues around a powerful gene-editing technology. From 9 July.

    Read
    Our Biggest Experiment, by campaigner and science communicator Alice Bell, is the one we have been conducting on our own climate. She chronicles centuries-old attempts to acquire and manage the energy we need.Advertisement
    AIG/THE FARM 51
    Play
    Chernobylite – released early on Steam, with the complete version out later this month – is a scary survival game set in a beautiful and accurate 3D-scanned recreation of the exclusion zone around the Chernobyl nuclear power station. More

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    Jungle review: How tropical forests helped shape human evolution

    By Michael Marshall

    FOR many of the people reading this, tropical forests are remote places. A few may have visited the Amazon on holiday, or ventured into the Bornean rainforests to see orangutans, but for most, tropical forests seem far removed from everyday life.
    In Jungle, his first book for a general audience, archaeologist Patrick Roberts sets out to tear down the barriers and show us how our lives are intertwined with tropical forests, “to convince you that the history of tropical forests is your history too”.
    To do so, Roberts has written a history of the world according to the tropics and their jungles. He begins with the first land plants and the origins of trees, sketching how they affected the dinosaurs, early mammals and first primates.
    The middle third of the book is devoted to the role of tropical forests in human evolution. A key message is that tropical forests aren’t inhospitable: people have lived in them for hundreds of thousands of years. Roberts attacks the long-standing idea that our ancestors left the trees to live on grasslands. Early hominins clearly spent less time up trees than apes such as chimpanzees, but the evidence suggests that our ancestors lived in many places, from the most open savannah to dense forests. More recently, people living in tropical forests have built city-like settlements, as in the Amazon.
    Roberts moves on to document how the European empires of the past few centuries wrought havoc on the people and ecosystems of the tropics: for instance, by setting up the global trades in sugar and rubber, and exploitative labour systems such as slavery on which they relied. He brings the story up to date by outlining the multiplying threats the forests face from climate change, agriculture and wildfires, ending with pleas for their preservation. If we don’t save the tropical forests, warns Roberts, “climate change, declining food sources, economic catastrophe, political instability, mass migration and an explosion of pandemic diseases will very soon be knocking at your own door”.
    In short, Jungle is enormously ambitious for a first popular book: it spans hundreds of millions of years and ranges across many disciplines. Does Roberts pull it off? Sort of.
    On an intellectual and factual level, he unquestionably succeeds. Jungle is deeply researched, and moves with great skill from ecology and evolution to history and politics. Roberts handles them deftly, rarely putting a foot wrong.
    Where the book does fall down is its writing style. This is so dry and complicated it might as well be an academic text. Sentences routinely run over five lines and paragraphs sprawl over whole pages. Vast arrays of facts and figures are hurled at the reader, largely unleavened by humour, anecdote or anything else.
    This is compounded by a generally grim tone. Even the early chapters on evolution and dinosaurs, in which you might expect joy, thrills or awe before the serious stuff kicks in, are tough going. And the final five chapters, where Roberts outlines how modern capitalism abused tropical forests and its peoples, are an almost unbearable trudge through what feels like an endless series of atrocities.
    “Jungle is enormously ambitious for a first popular book: it spans millions of years and many disciplines”
    I am not suggesting Roberts should have dialled back his message: why should he, when he is so plainly correct? Moreover, some readers may not mind the style, while students looking for a panoramic and detailed survey of tropical forests will get a lot out of Jungle. But its difficult style and dourness will limit the appeal, which is a shame because its message should be heard.
    For me, Jungle‘s biggest problem is that while it does a superb job of conveying the factual and rational reasons why we should all care about tropical forests, it doesn’t make you feel it in your bones.

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    New fossil finds show we are far from understanding how humans evolved

    Chuang Zhao
    LAST week saw the announcement of not one but two groups of ancient humans, both new to science, and there is no reason to think the discoveries will stop any time soon.
    In Israel, a team of researchers discovered bones from a member of a population that apparently lived in the area between 420,000 and 120,000 years ago. These hominins, which the team calls Nesher Ramla Homo, looked a bit like the Neanderthals, and the team claims that members of the new-found group were the Neanderthals’ ancestors. Not everyone agrees, however, and other interpretations have already been … More