[b]The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 450 Aug 13th

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    Electronic News Bulletin No. 450 2017 August 13

    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/

    University of California – Los Angeles

    The Sun's core rotates nearly four times faster than its surface,
    according to new findings by an international team of astronomers.
    Scientists had assumed that the core rotates at about the same speed
    as the surface. The most likely explanation is that the core rotation
    is left over from the period when the Sun formed, some 4.6 billion
    (U.S. billion, = 10 to the 9, throughout this Bulletin) years ago.
    The rotation of the solar core may give us a clue as to how the Sun
    formed. After the Sun formed, the solar wind probably slowed down
    the rotation of the outer layers. The rotation might also affect
    sunspots, which also rotate. Sunspots can be enormous; a single
    sunspot can be larger than the Earth. The researchers studied surface
    acoustic waves in the Sun's atmosphere, some of which penetrate to the
    Sun's core, where they interact with gravity waves that have a slosh-
    ing motion similar to how water would move in a half-filled tanker
    lorry driven on a winding mountain road. From those observations,
    they detected the sloshing motions of the solar core. By carefully
    measuring the acoustic waves, the researchers determined precisely
    the time it takes an acoustic wave to travel from the surface to the
    centre of the Sun and back again. That travel time turned out to be
    influenced slightly by the sloshing motion of the gravity waves.
    The researchers identified the sloshing motion and made the calcula-
    tions using 16 years of observations from an instrument called GOLF
    (Global Oscillations at Low Frequency) on a spacecraft called SoHO
    (the Solar and Heliospheric Observatory) — a joint project of ESA
    and NASA. The method was developed by researchers at the Observatoire
    de la Cote d'Azur in Nice. The idea that the solar core could be
    rotating more rapidly than the surface has been considered for more
    than 20 years, but has never before been measured. The core of the
    Sun differs from its surface in another way as well. The core has a
    temperature of approximately 15.7 million degrees Kelvin, whereas the
    surface is `only' 5,800 Kelvin.

    National Radio Astronomy Observatory

    Saturn's largest moon, Titan, is one of our Solar System's most
    intriguing and Earth-like bodies. It is nearly as large as Mars and
    has a hazy atmosphere made up mostly of nitrogen with a smattering of
    organic (i.e. carbon-based) molecules, including methane (CH4) and
    ethane (C2H6). Planetary scientists theorize that that chemical
    make-up is similar to the Earth's primordial atmosphere. The con-
    ditions on Titan, however, are not conducive to the formation of life
    as we know it; it is simply too cold. At ten times the distance from
    the Earth to the Sun, Titan is so cold that liquid methane rains onto
    its solid icy surface, forming rivers, lakes, and seas. The pools of
    hydrocarbons, however, create a unique environment that may help
    molecules of vinyl cyanide (C2H3CN) link together to form membranes,
    features resembling the lipid-based cell membranes of living organisms
    on Earth. Astronomers using archival data from the Atacama Large
    Millimeter/submillimeter Array (ALMA), which were collected over
    a series of observations from February to May 2014, have found
    compelling evidence that molecules of vinyl cyanide are indeed
    present on Titan in significant quantities. By reviewing the archival
    data, astronomers found three distinct signals — spikes in the
    millimetre-wavelength spectrum — that correspond to vinyl cyanide.
    Those telltale signatures originated at least 200 kilometres above
    the surface of Titan.
    Titan's atmosphere is a veritable chemical factory, harnessing the
    light of the Sun and the energy from fast-moving particles that orbit
    around Saturn to convert simple organic molecules into larger, more
    complex chemicals. As our knowledge of Titan's chemistry grows, it
    becomes increasingly apparent that complex molecules arise naturally
    in environments similar to those that existed on the early Earth, but
    there are important differences. For example, Titan is much colder
    than the Earth ever was at any period in its history. The temperature
    on Titan averages about 95°K, so water at its surface remains frozen.
    Geological evidence also suggests that the early Earth had high
    concentrations of carbon dioxide (CO2); Titan does not. The Earth's
    rocky surface was also frenetically active, with extensive vulcanism
    and routine asteroid impacts, which would have affected the evolution
    of our atmosphere. In comparison, Titan's icy crust appears quite
    docile. The team is looking for new and more complex organic
    chemicals as well as studying Titan's atmospheric circulation
    patterns. In the future, higher-resolution studies will shed more
    light on that intriguing satellite, and possibly give us new insights
    into Titan's potential for prebiotic chemistry.


    Could the next flyby target for NASA's New Horizons spacecraft
    actually be two targets? New Horizons scientists look to answer that
    question as they sort through new data gathered on the distant Kuiper-
    Belt object (KBO) 2014 MU69, which the spacecraft will fly past on
    2019 Jan. 1. That flyby will be the most distant in the history of
    space exploration, a (US-)billion miles beyond Pluto. The ancient
    KBO, which is more than 6.5 billion kilometres away, passed in front
    of a star on 2017 July 17. A number of telescopes deployed by the New
    Horizons team in a remote part of Patagonia were in the right place at
    the right time to catch the fleeting occultation, and were able to
    capture important data to help mission planners refine the spacecraft
    trajectory and understand the size, shape, orbit and environment
    around MU69.

    On the basis of those new occultation observations, team members say
    that MU69 may not be not a lone spherical object, but suspect it could
    be an `extreme prolate spheroid', or even a binary pair. The odd
    shape has scientists thinking that two bodies may be orbiting very
    close together or even touching (a system known as a close or contact
    binary), or perhaps they are observing a single body with a large
    chunk taken out of it. The size of MU69 or its components also can be
    determined from the data. It appears to be no more than 30 km long,
    (or, if it is binary, each component is about 15-20 km in diameter).
    The July 17 stellar occultation event that gathered the data was the
    third of a historic set of three ambitious occultation observations
    for New Horizons. The team used data from the Hubble telescope and
    the Gaia satellite to calculate whereabouts the shadow of MU69 would
    fall on the Earth's surface.

    NASA/Goddard Space Flight Center

    At only four light-years away, Proxima b is our closest known extra-
    solar neighbour. However, owing to the fact that it has not been seen
    crossing in front of its host star, the exoplanet eludes the usual
    method for learning about its atmosphere. Instead, scientists must
    rely on models to understand whether it is habitable. One computer
    model considered what would happen if the Earth orbited Proxima
    Centauri, our nearest stellar neighbour and Proxima b's host star, in
    an orbit analogous to that of Proxima b. The study suggests that the
    Earth's atmosphere would not survive in close proximity to the violent
    red dwarf. Just because Proxima b's orbit is in the habitable zone,
    which is the distance from its host star where water could pool on a
    planet's surface, does not mean that it is habitable. It does not
    take into account, for example, whether water actually exists on the
    planet, or whether an atmosphere could survive in that orbit.
    Atmospheres are also essential for life as we know it: having the
    right atmosphere allows for climate regulation, the maintenance of a
    water-friendly surface pressure, shielding from hazardous space
    weather, and the housing of life's chemical building blocks. The
    computer model used the Earth's atmosphere, magnetic field and gravity
    as proxies for Proxima b's. It also calculated how much radiation
    Proxima Centauri produces on average, on the basis of observations
    from the Chandra X-ray Observatory. With those data, the model
    simulates how the host star's intense radiation and frequent flaring
    affect the exoplanet's atmosphere. An active red dwarf star like
    Proxima Centauri strips away atmosphere when high-energy extreme-UV
    radiation ionizes atmospheric gases, knocking off electrons and
    producing a lot of electrically charged particles. In that process,
    the newly formed electrons gain enough energy that they can readily
    escape the planet's gravity and race out of the atmosphere. Opposite
    charges attract, so as more negatively charged electrons leave the
    atmosphere, they create a powerful charge separation that pulls
    positively charged ions along with them, out into space.
    In Proxima Centauri's habitable zone, Proxima b encounters bouts of
    extreme ultraviolet radiation hundreds of times greater than the Earth
    does from the Sun. That radiation generates enough energy to strip
    away not just the lightest molecules — hydrogen — but also, over
    time, heavier elements such as oxygen and nitrogen. The model shows
    that Proxima Centauri's powerful radiation drains the Earth-like
    atmosphere as much as 10,000 times faster than happens at the Earth.
    To understand how the process can vary, the scientists looked at two
    other factors that exacerbate atmospheric loss. First, they
    considered the temperature of the neutral atmosphere, called the
    thermosphere. They found that, as the thermosphere heats with more
    stellar radiation, atmospheric escape increases. The scientists also
    considered the size of the region over which atmospheric escape
    happens, the polar cap. Planets are most sensitive to magnetic
    effects at their magnetic poles. When magnetic field lines at the
    poles are closed, the polar cap is limited and charged particles
    remain trapped near the planet. On the other hand, greater escape
    occurs when magnetic field lines are open, providing a one-way route
    out into space. The scientists show that with the highest thermo-
    sphere temperatures and a completely open magnetic field, Proxima b
    could lose an amount equal to the whole of the Earth's atmosphere in
    100 million years — which is only a small fraction of Proxima b's
    4 billion years thus far. When the scientists assumed the lowest
    temperatures and a closed magnetic field, that much mass escapes
    over 2 billion years. Red dwarfs like Proxima Centauri or the
    TRAPPIST-1 star are often the target of exoplanet hunts, because
    they are the coolest, smallest and most common stars in the Galaxy.
    Because they are cooler and dimmer, planets have to be in small
    orbits for liquid water to be present. But unless the atmospheric
    loss is counteracted by some other process — such as a massive amount
    of volcanic activity or comet bombardment — such close proximity is
    not promising for an atmosphere's survival or sustainability.


    In a first-of-its-kind analysis, Northwestern University astrophys-
    icists have discovered that, contrary to previous supposition, up to
    half of the matter in our Milky Way galaxy may have come from distant
    galaxies. As a result, each one of us may be made in part from
    extragalactic matter. Using supercomputer simulations, the research
    team found a major and unexpected new mode for how galaxies, including
    our own Milky Way, acquired their matter: intergalactic transfer.
    The simulations show that supernova explosions eject copious amounts
    of gas from galaxies, which causes atoms to be transported from one
    galaxy to another by powerful galactic winds. Intergalactic transfer
    is a newly identified phenomenon, which simulations indicate could
    be critical for understanding how galaxies evolve. Galaxies are far
    apart from each other, so even though galactic winds propagate at
    several hundred km/s, this process occurred over several billion
    years. The research group had developed sophisticated numerical
    simulations that produced realistic 3D models of galaxies, following a
    galaxy's formation from just after the Big Bang to the present day.
    It then developed state-of-the-art algorithms to mine that wealth of
    data and quantify how galaxies acquire matter from the Universe.
    By tracking in detail the complex flows of matter in the simulations,
    the research team found that gas flows from smaller galaxies to larger
    galaxies, such as the Milky Way, where the gas forms stars. Such
    transfer of mass through galactic winds can account for up to 50% of
    matter in the larger galaxies. In a galaxy, stars are bound together:
    a large collection of stars orbits a common centre of mass. After the
    Big Bang 14 billion years ago, the Universe was filled with a uniform
    gas — no stars, no galaxies. But there were tiny perturbations in
    the gas, and they started to grow by force of gravity, eventually
    forming stars and galaxies. After galaxies formed, each had its own
    identity. The findings open a new line of research in understanding
    galaxy formation, the researchers say, and the prediction of inter-
    galactic transfer can now be tested. The Northwestern team plans to
    collaborate with observational astronomers who are working with the
    Hubble telescope and ground-based observatories to test the simulation

    Arizona State University

    Astronomers have discovered 23 young galaxies, seen as they were 800
    million years after the Big Bang. Long ago, about 300,000 years after
    the Big Bang, the Universe was dark. There were no stars or galaxies,
    and the Universe was filled with neutral hydrogen gas. In the next
    half-billion years or so the first galaxies and stars appeared. Their
    energetic radiation ionized their surroundings, illuminating and
    transforming the Universe. That dramatic transformation, known as
    re-ionization, occurred some time in the interval between 300 million
    years and one billion years after the Big Bang. Astronomers are
    trying to pinpoint that milestone more precisely, and the galaxies
    found in this study help in that determination. Before re-ionization,
    the galaxies were very hard to see, because their light is scattered
    by inter-galactic gas, like a car's headlights in fog. As enough
    galaxies turn on and 'burn off the fog' they become easier to see.
    By doing so, they help to provide a diagnostic to see how much of the
    'fog' remains at any time in the early Universe. To detect such
    galaxies, astronomers have been using the Dark Energy Camera (DECam),
    a powerful new instrument installed at the 4-m Blanco Telescope at
    CTIO in northern Chile.
    The galaxy search using the Arizona-designed filter and DECam is part
    of the ongoing `Lyman-Alpha Galaxies in the Epoch of Reionization'
    project (LAGER). It is the largest uniformly selected sample that
    goes far enough back in the history of the Universe to reach cosmic
    dawn. The combination of the large survey size and sensitivity of
    that survey enables astronomers to study galaxies that are common but
    faint, as well as those that are bright but rare, at that early stage
    in the Universe. The findings in the survey imply that a large
    fraction of the first galaxies that ionized and illuminated the
    Universe formed early, less than 800 million years after the Big Bang.
    The next steps for the team will be to build on those results. They
    plan to continue to search for distant star-forming galaxies over a
    larger volume of the Universe and to investigate further the natures
    of some of the first galaxies in the Universe.


    Humanity's most distant and longest-lived spacecraft, Voyager 1 and 2,
    achieve 40 years of operation this August and September. Despite
    their vast distance, they continue to communicate with NASA daily.
    Their story has not only informed generations of current and future
    scientists and engineers, but also the Earth's culture, including
    film, art and music. Each spacecraft carries a golden record of Earth
    sounds, pictures and messages. Since the spacecraft could last
    billions of years, those circular time capsules could one day be the
    only traces of human civilization. The Voyagers have set numerous
    records in their journeys. In 2012, Voyager 1, which was launched on
    1977 Sept. 5, became the first spacecraft that could be claimed to
    have entered interstellar space. Voyager 2, launched on 1977 Aug. 20,
    is the only spacecraft to have flown by all four outer planets —
    Jupiter, Saturn, Uranus and Neptune. The two spacecrafts' numerous
    planetary encounters include discovering the first active volcanoes
    beyond the Earth, on Jupiter's moon Io; hints of a subsurface ocean on
    Jupiter's moon Europa; the most Earth-like atmosphere in the Solar
    System, on Saturn's moon Titan; the jumbled-up, icy moon Miranda at
    Uranus; and icy-cold geysers on Neptune's moon Triton. Though the
    spacecraft have left the planets far behind — and neither will come
    remotely close to another star for 40,000 years — the two probes
    still send back observations about conditions where our Sun's
    influence diminishes and interstellar space begins.
    Voyager 1, now almost 13 billion miles from the Earth, travels through
    interstellar space northward, out of the plane of the planets. The
    probe has informed researchers that cosmic rays (atomic nuclei
    accelerated to nearly the speed of light) are as much as four times
    more abundant in interstellar space than in the vicinity of the Earth.
    That means that the heliosphere, the bubble-like volume containing our
    Solar System's planets and solar wind, effectively acts as a radiation
    shield for the planets. Voyager 1 also hinted that the magnetic field
    of the local interstellar medium is wrapped around the heliosphere.
    Voyager 2, now almost 11 billion miles from the Earth, travels south
    and is expected to enter interstellar space in the next few years.
    The difference in the locations of the two Voyagers allows scientists
    to compare already two regions of space where the heliosphere
    interacts with the surrounding interstellar medium, using instruments
    that measure charged particles, magnetic fields, low-frequency radio
    waves and solar-wind plasma. Once Voyager 2 crosses into the inter-
    stellar medium, the two spacecraft will be able to sample the medium
    from two different locations simultaneously. The twin Voyagers have
    been cosmic over-achievers, thanks to the foresight of mission
    designers. By preparing for the radiation environment at Jupiter, the
    harshest of all the planets in the Solar System, the spacecraft were
    well equipped for their subsequent journeys. Both Voyagers carry
    redundant systems that allow them to switch to backup systems
    autonomously when necessary, as well as long-lasting power supplies.
    Each Voyager has three radio-isotope thermoelectric generators,
    devices that use the heat energy generated from the decay of
    plutonium-238, which has a half-life of 88 years.
    Because the Voyagers' power supplies decrease by four watts per year,
    engineers are havng to learn how to operate the spacecraft under ever-
    tighter power constraints. And to maximize the Voyagers' lifespans,
    they also have to understand documents written decades earlier
    describing commands and software, in addition to tapping the expertise
    of former Voyager engineers. Team members estimate that they will
    have to turn off the last scientific instrument by 2030. However,
    even after the spacecraft go silent, they will continue on their
    trajectories at about their present speed of some 48,000 kph,
    completing an orbit of the Milky Way every 225 million years.

    Bulletin compiled by Clive Down
    (c) 2017 The Society for Popular Astronomy

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