THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 483 2018 Dec 30th

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    THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 483 2018 December 30

    Here is the latest round-up of news from the Society for Popular
    Astronomy. The SPA is arguably Britain's liveliest astronomical
    society, with members all over the world. We accept subscription
    payments online at our secure site and can take credit and debit
    cards. You can join or renew via a secure server or just see how
    much we have to offer by visiting http://www.popastro.com/

    OSIRIS-REx CONFIRMS WATER ON ASTEROID
    NASA

    Early data from the Origins, Spectral Interpretation, Resource
    Identification, Security-Regolith Explorer (OSIRIS-REx) mission revealed
    water locked inside Bennu. Data collected by the probe's two spectrometers,
    OVIRS and OTES, revealed the presence of hydroxyls, molecules featuring
    bonded oxygen and hydrogen atoms. Scientists believe that those hydroxyl
    groups exist across the asteroid in water-bearing clay minerals, suggesting
    that, at some point, Bennu's rocky surface interacted with water.
    OSIRIS-REx arrived at its asteroid target earlier this month. Shortly after
    its rendezvous, the probe's instruments began surveying the asteroid. In
    addition to studying the chemical composition of Bennu's surface, the
    spacecraft's instruments are helping scientists map the asteroid's shape and
    contours. OSIRIS-REx's surveying efforts will continue for the next year.
    Over the next several months, the probe will execute a series of fly-bys to
    get a closer look at some of Bennu's features. The spacecraft will swoop by
    the asteroid's equator and poles. Some of the approaches will put the probe
    within 4.4 miles of the asteroid's surface. With each fly-by, the maps of
    Bennu will become more detailed. Scientists will also use OSIRIS-REx's
    observations to refine estimates of the asteroid's mass and spin rate. The
    new data will help scientists to understand better how asteroids form and
    evolve. Updated maps will also help OSIRIS-REx to perfect its orbit around
    the asteroid, as well as to identify points of interest. The data will also
    help scientists choose where OSIRIS-REx will reach down with its robotic arm
    and scoop up regolith — rocks and dust — from Bennu's surface. The
    earliest observations show that Bennu has a balanced mix of heavily
    bouldered regions and relatively smooth areas. The third New Frontiers
    planetary science mission (following Juno and New Horizons), OSIRIS-REx is
    expected to return to Earth with a collected specimen in 2023 September.

    EVIDENCE FOR CARBON-RICH SURFACE ON CERES
    Southwest Research Institute

    Astronomers have concluded that the surface of dwarf planet Ceres is rich in
    organic matter. Data from the Dawn spacecraft indicate that Ceres's surface
    may contain several times the concentration of carbon that is present in the
    most carbon-rich primitive meteorites found on Earth. Ceres is believed to
    have originated about 4.6 billion years ago at the dawn of our Solar System.
    Dawn data previously revealed the presence of water and other volatiles,
    such as ammonium derived from ammonia, and now a high concentration of
    carbon. That chemistry suggests that Ceres formed in a cold environment,
    perhaps outside the orbit of Jupiter. An ensuing shake-up in the orbits of
    the large planets would have pushed Ceres to its current location in the
    main asteroid belt, between the orbits of Mars and Jupiter. Geophysical,
    compositional and collisional models based on Dawn data revealed that Ceres'
    partially differentiated interior has been altered by fluid processes.
    Dawn's Visible and Infrared Mapping Spectrometer has shown that the overall
    low albedo of Ceres' surface is a combination of rock–water interaction
    products such as phyllosilicates and carbonates and a significant amount of
    spectrally neutral darkening agents, such as magnetite, an iron oxide.
    Because Dawn's Gamma Ray and Neutron Detector limits magnetite to only a few per cent by mass, the data point to the presence of an additional darkening
    agent, probably amorphous carbon. Interestingly, specific organic compounds
    have also been detected near a 31-mile-wide impact crater named Ernutet,
    giving further support to the notion of widespread presence of organics in
    Ceres' shallow subsurface. The new study also finds that 50-60 per cent of
    Ceres' upper crust may have a composition similar to that of primitive
    carbonaceous chondrite meteorites. That material is compatible with contam-
    ination from infalling carbonaceous asteroids, a possibility supported by
    Ceres' battered surface.

    THE MYSTERY OF ULTIMA THULE
    Spaceweather.com

    When NASA's New Horizons spacecraft flew past Pluto three years ago, mission
    scientists watching the first close-up images were shocked. Despite being
    stuck in the deep freeze of the Solar System 6 billion km from the Sun,
    Pluto was not the frozen world that many expected it to be. It was alive
    with mountain ranges, windswept dunes, bladed terrain and much more. In one
    quick fly-by, New Horizons turned planetary science on its head. New
    Horizons is now less than 2 weeks away from a new world even less known than
    Pluto. Its name is 'Ultima Thule' (2014 MU69), which means means 'beyond
    the borders of the known world'. Indeed, the little space rock is
    profoundly unknown. Located almost a billion kilometres farther from the
    Sun than Pluto, Ultima Thule has never been much more than a faint speck of
    light in telescopes. It inhabits the distant Kuiper Belt. On New Year's
    Eve and New Year's Day, New Horizons will swoop three times closer to Ultima
    Thule than it flew past Pluto in July 2015, shattering previous records for
    the most distant body explored by a spacecraft. First images will be posted
    on a web site set up by the New Horizons' team: SeeUltimaThuleNow.com .
    We already know one thing about Ultima Thule. Its shape is elongated and
    strange. In 2017, astronomers watched a distant star pass behind Ultima
    Thule. Starlight winked in and out in a pattern suggesting two lobes with
    diameters of 20 and 18 km, respectively. Ultima Thule could be a small
    binary system. Ultima Thule is 100 times smaller than Pluto, but its
    scientific value is incalculable. From everything we know, it was formed
    4.5 or 4.6 billion years ago, 4 billion miles from the Sun. It has been
    remained at that enormous distance from the Sun, at a temperature of nearly
    absolute zero, ever since, so it probably represents the best sample of the
    ancient solar nebula ever studied.

    MOST-DISTANT SOLAR-SYSTEM OBJECT OBSERVED
    Carnegie Institution for Science

    A team of astronomers has discovered the most-distant body ever observed in
    our Solar System. It is the first known Solar-System object that has been
    detected at a distance that is more than 100 times farther than the Earth is
    from the Sun. The new object has been given the provisional designation
    2018 VG18. 2018 VG18, nicknamed 'Farout' by the discovery team for its
    extremely distant location, is at about 120 astronomical units (AU). The
    second-most-distant observed Solar-System object is Eris, at about 96 AU.
    Pluto is currently at about 34 AU, making 2018 VG18 more than three and a
    half times more distant than the Solar System's most-famous dwarf planet.
    2018 VG18 was discovered as part of the team's continuing search for
    extremely distant Solar-System objects, including the suspected Planet X,
    which is sometimes also called Planet 9. In October, the same group of
    researchers announced the discovery of another distant Solar-System object,
    called 2015 TG387 and nicknamed 'The Goblin' because it was first seen near
    Halloween. The Goblin was discovered at about 80 AU and has an orbit that
    is consistent with its being influenced by an unseen Super-Earth-sized
    Planet X on the Solar System's very distant fringes. The existence of a
    ninth major planet at the fringes of the Solar System was first proposed by
    that same research team in 2014 when they discovered 2012 VP113, nicknamed
    Biden, which is currently near 84 AU.
    2015 TG387 and 2012 VP113 never get close enough to the Solar System's giant
    planets, like Neptune and Jupiter, to have significant gravitational
    interactions with them. That means that those extremely distant objects can
    be probes of what is happening in the Solar System's outer reaches. The
    team does not know 2018 VG18's orbit very well yet, so it has not been able
    to determine if it shows signs of being shaped by Planet X. 2018 VG18 is
    much more distant and slower-moving than any other observed Solar-System
    object, so it will take a few years to determine its orbit fully. But it
    was found in a similar location in the sky to the other known extreme Solar
    System objects, suggesting that it might have the same type of orbit that
    most of them do. The orbital similarities shown by many of the known small,
    distant Solar-System bodies was the catalyst for the original assertion that
    there is a distant, massive planet at several hundred AU shepherding those
    smaller objects. All that we currently know about 2018 VG18 is its extreme
    distance from the Sun, its approximate diameter, and its colour. Because
    2018 VG18 is so distant, it orbits very slowly, probably taking more than
    1,000 years to take one trip around the Sun. The discovery images of 2018
    VG18 were taken by the Japanese Subaru 8-m telescope on Mauna Kea in Hawaii on 2018 November 10. Once 2018 VG18 was found, it needed to be re-observed to confirm its very distant nature. (It takes multiple nights of observing
    to determine an object's distance.) 2018 VG18 was seen for the second time
    in early December at the Magellan telescope at Las Campanas Observatory in
    Chile. The Magellan observations confirmed that 2018 VG18 is at around
    120 AU, making it the first Solar-System object observed beyond 100 AU.
    Its brightness suggests that it is about 500 km in diameter. It has a
    pinkish hue, a colour generally associated with ice-rich objects.

    WHERE DID ALL THE NEPTUNES GO?
    Universite de Geneve

    “But where did the hot Neptunes go?” That is a question astronomers have
    been asking for a long time, faced with the mysterious absence of planets
    the size of Neptune very close to their stars. A team of researchers has
    just discovered that one such planet is losing its atmosphere at a frantic
    pace. That observation strengthens the theory that hot Neptunes have lost
    much of their atmospheres and turned into smaller planets called
    super-Earths, which are much more numerous. Fishermen would be puzzled if
    they netted only big and little fish, but few medium-sized fish. That is
    similar to what happens to astronomers hunting exoplanets. They found a
    large number of hot planets the size of Jupiter and numerous others a little
    larger than the Earth (called super-Earths, whose diameters do not exceed
    1.5 times that of the Earth), but no planets close to their star the size of
    Neptune. The mysterious 'desert' of hot Neptunes suggests two explanations:
    either such worlds are rare, or that they were plentiful at one time, but
    have since disappeared. A few years ago, UNIGE astronomers using NASA's
    Hubble Space Telescope discovered that a warm Neptune on the edge of the
    desert, GJ 436b, was losing hydrogen from its atmosphere. The loss is not
    enough to threaten the atmosphere of GJ 436b, but suggested that Neptunes
    receiving more energy from their star could evolve more dramatically. That
    has just been confirmed by the same astronomers, members of the national
    research centre PlanetS. They observed with Hubble that another warm
    Neptune at the edge of the desert, named GJ 3470b, is losing its hydrogen
    100 times faster than GJ 436b. The two planets reside about 3.7 million
    kilometres from their star, one-tenth the distance between Mercury and the
    Sun, but the star hosting GJ 3470b is much younger and energetic. The team
    estimates that GJ 3470b has already lost more than a third of its mass.
    Observing the evaporation of two warm Neptunes is encouraging, but team
    members know that they need to study more of them to confirm their
    predictions. Unfortunately, the hydrogen that escapes from these planets
    cannot be detected if they are more than 150 light-years from Earth
    (GJ 3470b is 97 light-years away), because hydrogen is then hidden by
    interstellar gas. Researchers thus plan to use Hubble to look for other
    traces of atmospheric escape, because hydrogen could drag upwards heavier
    elements such as carbon. The solution could also come from helium, whose
    infrared radiation is not blocked by the interstellar medium.

    DID SUPERNOVAE KILL OFF LARGE OCEAN ANIMALS?
    University of Kansas

    About 2.6 million years ago, an oddly bright light arrived in the pre-
    historic sky and lingered there for weeks or months. It was a supernova
    some 150 light-years away. Within a few hundred years, long after the
    strange light in the sky had dwindled, a tsunami of cosmic energy from that
    same shattering star explosion could have reached our planet and pummelled
    the atmosphere, touching off climate change and triggering mass extinctions
    of large ocean animals, including a shark species that was the size of a
    school bus. Recent papers revealing ancient seabed deposits of iron-60
    isotopes provided the compelling evidence of the timing and distance of
    supernovae. Because iron-60 is radioactive, if it had formed with the Earth
    it would be long gone by now. So it had to have been rained down on us.
    There is some debate about whether there was only one supernova really
    nearby or a whole chain of them. Studies of iron-60 residue reveal that
    there is a huge spike 2.6 million years ago, but there is excess scattered
    clear back 10 million years. According to astronomers, other evidence for a
    series of supernovae is found in the very architecture of the local
    Universe. We have the Local Bubble in the interstellar medium and we are
    right on its edge. It is a giant region about 300 light-years long. It is
    basically very hot, very low-density gas — nearly all the gas clouds have
    been swept out of it. The best way to manufacture a bubble like that is a
    number of supernovae that blow it bigger and bigger, and that seems to fit
    well with idea of a chain. Calculations are based on the idea that one
    supernova that goes off, and its energy sweeps by Earth, and it's over.
    But with the Local Bubble, the cosmic rays bounce off the sides and the
    cosmic-ray bath would last 10,000 to 100,000 years. That way, one could
    imagine a whole series of these things feeding more and more cosmic rays
    into the Local Bubble and giving us cosmic rays for millions of years.
    Whether or not there was one supernova or a series of them, the supernova
    energy that spread layers of iron-60 all over the world also caused
    penetrating particles called muons to shower the Earth, causing cancers and
    mutations — especially to larger animals. The best description of a muon
    would be a very heavy electron — but muons are a couple of hundred times
    more massive than electrons. They are very penetrating. Even normally,
    there are lots of them passing through us. Nearly all of them pass through
    harmlessly, yet about one-fifth of our radiation dose comes by muons. But
    when the wave of cosmic rays hits, multiply those muons by a few hundred.
    Only a small fraction of them will interact in any way, but when the number
    is so large and their energy so high, you get increased mutations and cancer
    — those would be the main biological effects. Scientists have estimated
    that the cancer rate would go up about 50% for something the size of a human
    — and the bigger you are, the worse it is. For an elephant or a whale, the
    radiation dose is much larger. A supernova 2.6 million years ago may be
    related to a marine megafaunal extinction at the Pliocene-Pleistocene
    boundary where 36 per cent of the genera were estimated to have become
    extinct. The extinction was concentrated in coastal waters, where larger
    organisms would catch a greater radiation dose from the muons. Indeed, one
    of the extinctions that happened 2.6 million years ago was Megalodon, a
    famously large and fierce marine animal inhabiting shallow waters. Damage
    from muons would extend down hundreds of metres into ocean waters, becoming
    less severe at greater depths. High-energy muons can reach deeper in the
    oceans, being the more relevant agent of biological damage as depth
    increases.

    LARGE POPULATION OF YOUNG PLANETS
    University of Nevada, Las Vegas

    Astronomers have catalogued nearly 4,000 exoplanets in orbit around distant
    stars. Though the discovery of those new-found worlds has taught us much,
    there is still a great deal that we do not know about the birth of planets
    and the precise cosmic recipes that spawn the wide array of planetary bodies
    that we have already uncovered, including so-called hot Jupiters, massive
    rocky worlds, icy dwarf planets, and — hopefully some day soon — distant
    analogues of the Earth. To help answer those and other intriguing
    questions, a team of astronomers has conducted the first large-sample,
    high-resolution survey of protoplanetary discs, the belts of dust and gas
    around young stars. Using the Atacama Large Millimetre/submillimetre Array
    (ALMA) telescope, researchers have obtained high-resolution images of 20
    nearby protoplanetary discs and given astronomers new insights into the
    variety of features they contain and the speed with which planets can
    emerge. It appears that in other parts of our Milky Way there is
    potentially a large population of young planets — similar in mass to
    Neptune or Jupiter — in wide orbits, that are not detectable by other
    current planet-searching techniques. That implies that many extra-solar
    systems may be similar to our Solar System in the sense that they also have
    planets like Uranus and Neptune at the outer disc.
    Understanding how the Earth was formed 4 billion years ago in our Solar
    System is difficult because the Solar System finished the planet-formation
    processes long ago. On the other hand, we can observe young stars in other
    parts of the Milky Way where young stars and young planets are currently
    being assembled. Since the young stars are far away from us, we need
    powerful telescopes, like ALMA, to study those systems. When stars are
    young, they are surrounded by flat discs made of gas and dust. Those discs,
    called protoplanetary discs, are where young planets are born (that is also
    why planetary orbits in the Solar System are coplanar, lying in a common
    plane around our Sun). It is very challenging, but, when we drop a pebble
    into a pond, it will lead to ripples in the pond, which are more visible.
    Similarly, when a young planet is present in its water pond (the proto-
    planetary disc), it will excite waves too. If the planet is massive enough,
    the waves become a tsunami and cause damage to the disc, forming a gap along
    the planet's orbit in the disc. ALMA can detect tiny ripples and gaps in
    protoplanetary discs.

    FOSSIL FROM THE BIG BANG
    W. M. Keck Observatory

    A relic cloud of gas, orphaned after the Big Bang, has been discovered in
    the distant Universe by astronomers using the world's most powerful optical
    telescope, the W. M. Keck Observatory on Mauna Kea. The discovery of such a
    rare fossil offers new information about how the first galaxies in the
    Universe formed. Everywhere we look, the gas in the Universe is polluted by
    waste heavy elements from exploding stars, but this particular cloud seems
    pristine, unpolluted by stars even 1.5 billion years after the Big Bang. If
    it has any heavy elements at all, it must be less than 1/10,000th of the
    proportion we see in the Sun. That is extremely low; the most compelling
    explanation is that it is a true relic of the Big Bang. The team used two
    of Keck Observatory's instruments — the Echellette Spectrograph and Imager
    (ESI) and the High-Resolution Echelle Spectrometer (HIRES) — to observe the
    spectrum of a quasar behind the gas cloud. The quasar, which emits a bright
    glow of material falling into a super-massive black hole, provides a light
    source against which the spectral shadows of the hydrogen in the gas cloud
    can be seen. The team targeted quasars where previous researchers had only
    seen shadows from hydrogen and not from heavy elements in lower-quality
    spectra. That allowed astronomers to discover such a rare fossil quickly
    with the precious time on the Keck Observatory's twin telescopes. The only
    two other fossil clouds known were discovered in 2011. The first two were
    serendipitous discoveries but until now no one has discovered anything
    similar — they are clearly very rare and difficult to see.

    Bulletin compiled by Clive Down (c) 2018 The Society for Popular Astronomy
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