THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 469 2018 May 20

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    THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 469 2018 May 20
    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/

    LOST ASTEROID RETURNS TO EARTH
    Spaceweather.com

    Last Monday the near-Earth asteroid 2010 WC9 moved across the constellation
    Hercules. On May 15, it flew through the Earth-Moon system, splitting the
    distance between our planet and the Moon. At its closest approach to us
    (203,000 km), the asteroid shone like an 11th-magnitude star as it raced
    through the southern constellation Pavo. 2010 WC9 is known as the 'lost
    asteroid' because astronomers lost track of it soon after it was discovered
    in 2010 November. The asteroid receded from the Earth and did not return
    for nearly 8 years … until now. Estimates of 2010 WC9's size range from
    60 to 130 m. That puts it in the same class as the Tunguska impactor, which
    levelled a forest in Siberia in 1908. And it is at least 3 times as large
    as the Chelyabinsk meteoroid, which exploded in the morning sky over Russia
    on 2013 Feb. 15, shattering windows and knocking people to the ground.
    There was no danger of a collision this time, though. Analysts are certain
    2010 WC9 will not hit the Earth in the foreseeable future. New observations
    of the asteroid in recent days have extended our knowledge of its orbit and
    eliminated the threat of collision for at least the next 100 years.

    NEW MAGNETIC PROCESS IN TURBULENT SPACE
    NASA/Goddard Space Flight Center

    Though close to home, the space immediately around Earth is full of hidden
    secrets and invisible processes. Scientists working with the Magnetospheric
    Multiscale spacecraft — MMS — have uncovered a new type of magnetic event
    in our near-Earth environment by using an innovative technique to squeeze
    extra information out of the data. Magnetic reconnection is one of the most
    important processes in the space — filled with charged particles known as
    plasma — around the Earth. That fundamental process dissipates magnetic
    energy and propels charged particles, both of which contribute to a dynamic
    space-weather system that scientists want to understand better, and even one
    day predict, as we do terrestrial weather. Reconnection occurs when crossed
    magnetic-field lines snap, explosively flinging away nearby particles at
    high speeds. The new discovery found reconnection where it has never been
    seen before — in turbulent plasma. Magnetic reconnection has been observed
    innumerable times in the magnetosphere — the magnetic environment around
    the Earth — but usually under calm conditions. The new event occurred in a
    region called the magnetosheath, just outside the outer boundary of the
    magnetosphere, where the solar wind is extremely turbulent. Previously,
    scientists did not even know whether reconnection could occur there, as the
    plasma is highly chaotic in that region. MMS found that it does, but on
    scales much smaller than previous spacecraft could probe.
    Even though the instruments aboard MMS are incredibly fast, they are still
    too slow to capture turbulent reconnection in action, which requires
    observing narrow layers of fast-moving particles hurled by the recoiling
    field lines. Compared to standard reconnection, in which broad jets of ions
    stream out from the site of reconnection, turbulent reconnection ejects
    narrow jets of electrons only a couple of miles wide. Magnetic reconnection
    occurs throughout the Universe, so that when we learn about it around our
    planet — where of course it is easiest for us to examine it — we can apply
    that information to other processes farther away. The finding of reconnec-
    tion in turbulence has implications, for example, for studies of the Sun.
    It may help scientists understand the role magnetic reconnection plays in
    heating the inexplicably hot solar corona — the Sun's outer atmosphere —
    and accelerating the supersonic solar wind. NASA's upcoming Parker Solar
    Probe mission is to be launched directly to the Sun in the summer of 2018 to
    investigate exactly those questions — and that research is all the better
    armed the more we understand about magnetic reconnection nearer home.

    WHAT WILL HAPPEN WHEN THE SUN DIES?
    University of Manchester

    Scientists agree that the Sun will die in approximately 10 billion
    years, but they were not sure what would happen next … until now.
    A team of international astronomers predicts that it will turn into a
    massive ring of luminous, interstellar gas and dust, known as a planetary
    nebula.
    Such nebulae mark the ends of 90% of all stars' active lives and trace a
    star's transition from a red giant to a degenerate white dwarf. But for
    years, scientists were not sure whether the Sun would follow that fate:
    it was thought to have too low mass to create a visible planetary nebula.
    To find out, the team developed a new stellar model that predicts the life
    cycle of stars. The model was used to predict the brightness (or lumin-
    osity) of the ejected envelope, for stars of different masses and ages.
    When a star dies it ejects a mass of gas and dust — known as its envelope
    — into space. The envelope can be as much as half the star's mass. That
    reveals the star's core, which by that point in the star's life is running
    out of fuel, eventually turning off before finally dying. It is only then
    that the hot core makes the ejected envelope shine brightly for around
    10,000 years — a brief period in astronomy. That is what makes the
    planetary nebula visible. Some are so bright that they can be seen from
    extremely large distances, tens of millions of light-years, whereas the
    star itself would be much too faint to see.
    The model also solves another problem that has been perplexing astronomers
    for a quarter of a century. Approximately 25 years ago astronomers
    discovered that if you look at planetary nebulae in another galaxy, the
    brightest ones always have the same brightness. It was found that it was
    possible estimate the distance of a galaxy just from the appearance of its
    brightest planetary nebulae. In theory it worked in any of type of galaxy.
    But while the data suggested that that was correct, the scientific models
    claimed otherwise. Old, low-mass stars should make much fainter planetary
    nebulae than young, more massive ones. The data said you could get bright
    planetary nebulae from low-mass stars like the Sun, but the models said that
    that was not possible, anything less than about twice the mass of the Sun
    would give a planetary nebula too faint to see. The new models show that
    after the ejection of the envelope, the stars heat up three times faster
    than was found by older models. That makes it much easier for a low-mass
    star, such as the Sun, to form a bright planetary nebula. The team found
    that in the new models, the Sun is almost exactly the lowest-mass star that
    still produces a visible, though faint, planetary nebula. Stars even a
    few per cent smaller do not. The team found that stars with masses less
    than 1.1 times the mass of the Sun produce fainter nebulae, and stars more
    massive than 3 solar masses brighter nebulae, but for the rest the
    predicted brightness is very close to what had been observed. Problem
    solved, after 25 years! Not only do we now have a way to measure the
    presence of stars of ages a few billion years in distant galaxies, which
    is a range that is remarkably difficult to measure, we have even found out
    what the Sun will do when it dies!

    WATER PLUMES ON EUROPA?
    NASA/Jet Propulsion Laboratory

    Scientists re-examining data from an old mission bring new insights to the
    tantalizing question of whether Jupiter's moon Europa has the ingredients
    to support life. The data provide independent evidence that the moon's
    sub-surface liquid-water reservoir may be venting plumes of water vapour
    above its icy shell. Data collected by the Galileo spacecraft in 1997 were
    put through new and advanced computer models to disentangle a mystery — a
    brief, localized bend in the magnetic field — that had gone unexplained
    until now. Previous ultraviolet images from the Hubble Space Telescope in
    2012 suggested the presence of plumes, but this new analysis used data
    collected much closer to the source and is considered strong, corroborating
    support for plumes. At the time of the 1997 fly-by, about 200 km above
    Europa's surface, the Galileo team did not suspect that the spacecraft
    might be grazing a plume erupting from the icy moon. When they re-examined
    the information gathered during that fly-by 21 years ago, sure enough, high-
    resolution magnetometer data showed something strange. Drawing on what
    scientists learned from exploring plumes on Saturn's moon Enceladus — that
    material in plumes becomes ionized and leaves a characteristic blip in the
    magnetic field — they knew what to look for. And there it was on Europa —
    a brief, localized bend in the magnetic field that had never been explained.
    Galileo carried a powerful Plasma Wave Spectrometer to measure plasma waves
    caused by charged particles in the gases of Europa's atmosphere. The team
    studied those data as well, and they also appeared to back the theory of a
    plume. But numbers alone could not paint the whole picture. The team
    layered the magnetometry and plasma-wave signatures into new 3D modelling
    which simulated the interactions of plasma with Solar-System bodies. The
    final ingredient was the data from Hubble that suggested the dimensions of
    potential plumes. The result that emerged, with a simulated plume, was a
    match to the magnetic field and plasma signatures that the team pulled
    from the Galileo data. There now seem to be too many lines of evidence to
    dismiss plumes at Europa. The findings are good news for the Europa
    Clipper mission, which may be launched as 'soon' as 2022 June. From its
    orbit of Jupiter, Europa Clipper will sail close by the moon in rapid,
    low-altitude fly-bys. If plumes are indeed spewing vapour from Europa's
    ocean or sub-surface lakes, Europa Clipper could sample the frozen liquid
    and dust particles. The mission team is gearing up now to look at potential
    orbital paths, and the new research will play into those discussions. If
    plumes exist, and we can directly sample what's coming from the interior of
    Europa, then we can more easily get at whether Europa has the ingredients
    for life.

    UNUSUAL ASTEROID DISCOVERED IN OUTER SOLAR SYSTEM
    ESO

    Astronomers have found that the Kuiper-Belt object 2004 EW95 is a carbon-
    rich asteroid, the first of its kind to be confirmed in the cold outer
    reaches of the Solar System. That curious object probably formed in the
    asteroid belt between Mars and Jupiter and has been flung billions of
    kilometres from its origin to its current home in the Kuiper Belt. The
    early days of our Solar System were a tempestuous time. Theoretical models
    of that period suggest that, after the gas giants formed, they rampaged
    through the Solar System, ejecting small rocky bodies from the inner Solar
    System to far-flung orbits at great distances from the Sun. In particular,
    those models suggest that the Kuiper Belt — a cold region beyond the orbit
    of Neptune — should contain a small fraction of rocky bodies from the inner
    Solar System, such as carbon-rich asteroids, referred to as carbonaceous
    asteroids. Now, a recent paper has presented evidence for the first
    reliably-observed carbonaceous asteroid in the Kuiper Belt, providing
    support for the theoretical models of our Solar System's troubled youth.
    After taking measurements from multiple instruments at the Very Large
    Telescope (VLT), a small team of astronomers was able to measure the
    composition of the anomalous Kuiper-Belt object 2004 EW95, and thus
    determined that it is a carbonaceous asteroid. That suggests that it
    originally formed in the inner Solar System and must since have migrated
    outwards. The peculiar nature of 2004 EW95 first came to light during
    routine observations with the Hubble Space Telescope. The asteroid's
    reflectance spectrum was different from that of similar small Kuiper-Belt
    objects (KBOs), which typically have uninteresting, featureless spectra
    that reveal little about their composition.
    The team observed 2004 EW95 with the X-Shooter and FORS2 instruments on the VLT. The sensitivity of those spectrographs allowed the team to obtain more
    detailed spectra of light reflected from the asteroid and thus to infer its
    composition. However, even with the light-collecting power of the VLT, 2004
    EW95 was still difficult to observe. Although the object is 300 kilometres
    across, it is currently four billion kilometres from the Earth, making
    gathering data from its dark, carbon-rich surface a demanding scientific
    challenge. Two features of the object's spectra were particularly eye-
    catching and corresponded to the presence of phyllosilicates and ferric
    oxides. The presence of those materials had never before been confirmed in
    a KBO, and they strongly suggest that 2004 EW95 formed in the inner Solar
    System. Given 2004 EW95's present-day abode in the icy outer reaches of the
    Solar System, that implies that it was flung out into its present orbit by
    a migratory planet in the early days of the Solar System. While there have
    been previous reports of other (atypical) Kuiper-Belt-object spectra, none
    was confirmed to this level of quality. The discovery of a carbonaceous
    asteroid in the Kuiper Belt is a key verification of one of the fundamental
    predictions of dynamical models of the early Solar System.

    HELIUM DETECTED IN ATMOSPHERE OF EXOPLANET
    ESA/Hubble Information Centre

    As far back as the year 2000, it was predicted that helium would be one
    of the most readily-detectable gases on giant exoplanets, but until now
    searches for it were unsuccessful. Now, astronomers using the Hubble
    telescope have detected it in the atmosphere of the exoplanet WASP-107b.
    Helium is the second-most-common element in the Universe after hydrogen.
    It is also one of the main constituents of Jupiter and Saturn in our Solar
    System. However, up till now helium had not been detected on exoplanets,
    despite searches for it. The team made the detection by analysing the
    infrared spectrum of the atmosphere of WASP-107b. Previous detections of
    extended exoplanet atmospheres have been made by studying the spectrum at
    ultraviolet and optical wavelengths; this detection therefore demonstrates
    that exoplanet atmospheres can also be studied at longer wavelengths. The
    strong signal measured from helium demonstrates a new technique to study
    upper layers of exoplanet atmospheres in a wider range of planets. Current
    methods, which use ultraviolet light, are limited to the closest exoplanets.
    We know that there is helium in the Earth's upper atmosphere, and this new
    technique may help us to detect atmospheres around Earth-sized exoplanets —
    which is otherwise very difficult with current technology. WASP-107b is one
    of the lowest-density planets known: while the planet is about the same size
    as Jupiter, it has only 12% of Jupiter's mass. It is about 200 light-years
    away and takes less than six days to orbit its host star. The amount of
    helium detected in the atmosphere of WASP-107b is so large that its upper
    atmosphere must extend tens of thousands of kilometres out into space. It
    is the first time that such an extended atmosphere has been discovered at
    infrared wavelengths. Since its atmosphere is so extended, the planet must
    be losing a significant amount of its atmospheric gases into space — from
    0.1 to 4% of its atmosphere's total mass every billion years.

    FASTEST-GROWING BLACK HOLE
    Astronomical Society of Australia

    Supermassive black holes at the centres of galaxies can get absurdly huge,
    sometimes reaching masses billions of times greater than that of the Sun.
    The rate at which black holes grow can vary, but Australian astronomers
    have detected one such object with an unusually intense appetite, making it
    the fastest-growing black hole ever detected. That bloated supermassive
    black hole has an equally bloated name, QSO SMSS J215728.21-360215.1, or
    J2157-3602 for short. As it is 12 billion light-years away, we are
    observing this bright behemoth not as it is today, but as it existed
    nearly four billion years after the Big Bang. Astronomers with the
    Australian National University (ANU) used three different instruments to
    observe the black hole, or quasi-stellar object (QSO) as it is also called:
    ESA's Gaia satellite, the ANU Siding Spring Observatory, and NASA's Wide-
    field Infrared Survey Explorer satellite. Observations show that J2157-3602
    is the size of about 20 billion suns, and is growing at a rate of 1% every
    million years. Every two days, that black hole devours a mass equivalent to
    our Sun, gobbling up dust, gas, bits of celestial debris, and whatever else
    it can suck in with its powerful gravitational influence. Astronomers have
    observed fast-growing QSOs before, but this one is a record-setter, making
    it the fastest-growing and the brightest-glowing black hole ever detected.
    The influx of gases is producing a tremendous amount of friction and heat,
    resulting in the high luminosity.
    The black hole is also shining ultraviolet light and X-rays at a rate that
    is rendering the entire galaxy sterile. If we had this monster sitting at
    the centre of our Milky Way galaxy, it would appear ten times brighter than
    the Full Moon. It would appear as an incredibly bright pinpoint star that
    would make the sky so bright as almost to wash out all the other stars.
    Supermassive black holes came into existence as early as 800 million years
    after the Big Bang, but how they grew so big and so quickly after the Big
    Bang remains a mystery. Scientists are now hoping to find black holes that
    are growing even faster than J2157-3602. Work in that area could tell us
    more about what the conditions were like in the early Universe, how elements
    were formed (especially metals), and how the early black holes may have
    ionized gases around them, making the Universe more transparent.

    Bulletin compiled by Clive Down
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