SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No 435 December 20th

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    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
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    NASA/Jet Propulsion Laboratory

    Researchers using the Mars Reconnaissance Orbiter have discovered
    that, frozen beneath a region of cracked and pitted plains on Mars,
    lies about as much water as is contained in Lake Superior, largest of
    the North-American Great Lakes. Scientists examined part of Mars'
    Utopia Planitia region, in the mid-northern latitudes, with the
    orbiter's ground-penetrating Shallow Radar (SHARAD) instrument.
    Utopia Planitia is a basin with a diameter of about 3,300 km,
    resulting from a major impact early in Mars' history and subsequently
    filled. Analyses of the radar data from more than 600 overhead passes
    reveal an ice deposit more extensive in area than the British Isles.
    The deposit ranges in thickness from about 80 to 170 metres, with a
    composition that is 50 to 85% water ice, mixed with dust or larger
    rocky particles. At the latitude of the deposit — about 45 degrees
    — ice cannot persist on the surface of Mars today; it sublimes into
    water vapour in the thin, dry atmosphere. The Utopia deposit is
    shielded from the atmosphere by a covering of soil, estimated to be
    about 1 to 10 metres thick. Mars today, with an axial tilt of 25
    degrees, accumulates large amounts of water ice at the poles. In
    cycles lasting about 120,000 years, the tilt varies to nearly twice
    that much, warming the poles and driving ice to middle latitudes.
    Climate modelling and previous findings of buried mid-latitude ice
    indicate that frozen water accumulates away from the poles during the
    long high-tilt periods.
    The newly surveyed ice deposit spans latitudes from 39 to 49 degrees
    within the plains. It represents less than 1% of all known water
    ice on Mars, but it more than doubles the volume of thick, buried
    ice sheets known in the northern plains. Ice deposits close to the
    surface are being considered as a resource for potential astronauts.
    The deposit described here is probably more accessible than most water
    ice on Mars, because it is at a relatively low latitude and it lies in
    a flat, smooth area where landing a spacecraft would be less hazardous
    than in some of the other areas where there is buried ice. The
    Utopian water is all frozen now. If there were a melted layer —
    which would be significant for the possibility of life on Mars — it
    would have been evident in the radar scans. However, some melting can
    not be ruled out during different climate conditions when the planet's
    axis was more tilted.
    Liverpool John Moores University

    Astronomers have discovered a new family of stars in the core of our
    Milky Way galaxy, providing new insights into the early stages of the
    Galaxy's formation. The discovery, made from the Sloan Digital Sky
    Survey, has shed new light on the origins of globular clusters. One
    of the projects of this collaboration is APOGEE (the Apache Point
    Observatory Galactic Evolution Experiment), which collects infrared
    data for hundreds of thousands of stars in the Milky Way. It was
    through observing stars in the infrared towards the Galactic Centre
    that the discovery was made of a new population of stars, the like
    of which had been seen before only inside globular clusters. That
    intriguing new family of stars could possibly have belonged to
    globular clusters that were destroyed during the violent initial
    formation of the Galactic centre, in which case there would have been
    about 10 times more globular clusters in the Milky Way in its early
    stages than there are today. That could mean that a substantial
    fraction of the old stars inhabiting the inner parts of the Galaxy
    today may have been formed initially in globular clusters that were
    later destroyed.
    The finding helps astronomers address fascinating questions such as
    what is the nature of the stars in the inner regions of the Milky Way,
    how globular clusters formed, and what role they played in the
    formation of the early Milky Way — and by extension the formation of
    other galaxies. The centre of the Milky Way is poorly understood,
    because it is blocked from view by intervening dust. Observing in the
    infrared, which is less absorbed by dust than visible light, APOGEE
    can see the centre of the Galaxy better than other methods. From the
    observations the chemical compositions of thousands of stars could be
    determined; among them was a considerable number of stars that
    differed from the bulk of those in the inner regions of the Galaxy,
    owing to their very high abundance of nitrogen. While not certain, it
    is suspected that those stars resulted from the destruction of
    globular clusters. They could also be the by-products of the first
    episodes of star formation taking place at the beginning of the
    Galaxy's history.

    National Astronomical Observatory of Japan

    Astronomers have found an extremely faint dwarf satellite galaxy of
    the Milky Way. The satellite lies in the direction of the constellation
    Virgo and has accordingly been named Virgo I. At an absolute
    magnitude of -0.8 in the optical waveband, it may well be the faintest
    satellite galaxy yet found. Its discovery suggests the presence of a
    large number of yet-undetected dwarf satellites in the halo of the
    Milky Way, and provides important insights into galaxy formation
    through hierarchical assembly of dark matter. Currently, some 50
    satellite galaxies of the Milky Way have been identified. About 40
    of them are faint and diffuse and belong to the category of 'dwarf
    spheroidal galaxies'. Many recently discovered dwarf galaxies,
    especially those found in systematic photometric surveys such as the
    Sloan Digital Sky Survey (SDSS) and the Dark Energy Survey (DES), are
    very faint, with absolute luminosities in the optical waveband less
    than -8 magnitude. They are called 'ultra-faint dwarf galaxies'.
    However, previous searches made use of telescopes of apertures 2.5 to
    4 metres, so only satellites relatively close to the Sun or those with
    brighter magnitudes were identified.
    The combination of the large aperture of the 8.2-m Subaru Telescope
    and the large field of view of the Hyper Suprime Cam (HSC) instrument
    is very powerful for this study. It enables an efficient search to
    be made for very faint dwarf satellites over large areas of the sky.
    The first step in searching for a new dwarf galaxy is to identify an
    over-density of stars in the sky, using photometric data. Next is to
    assess that the over-dense appearance is not due to line-of-sight or
    accidental juxtapositions of unrelated dense fields, but is really a
    stellar system. The standard method for doing that is to look for a
    characteristic distribution of stars in the colour-magnitude diagram
    (analogous to the Hertzsprung-Russell diagram). Stars in a general
    field show no particular patterns in this diagram. The team examined
    the early data of the Subaru Strategic Survey with HSC and found an
    apparent over-density of stars in Virgo with very high statistical
    significance, showing a characteristic pattern of an ancient stellar
    system in the colour-magnitude diagram. It is indeed a galaxy,
    because it is spatially extended with a radius of 124 light-years —
    larger than a globular cluster with comparable luminosity. The
    faintest dwarf satellites identified so far are Segue I, discovered by
    SDSS (-1.5 mag) and Cetus II in DES (0.0 mag). Cetus II is yet to be
    confirmed, as it is too compact as a galaxy, so Virgo I may turn out
    to be the faintest one so far discovered. It lies at a distance of
    280,000 light-years from the Sun, and such a remote galaxy with such a
    low luminosity has not been identified in previous surveys. It is
    beyond the reach of SDSS, which has previously surveyed the same area
    in the direction of the constellation Virgo.

    University of California – Riverside

    Galaxies formed and grew thousands of millions of years ago by
    accumulating gas from their surroundings, or colliding and merging
    with other young galaxies. Those early stages of galaxy assembly are
    believed to be accompanied by episodes of rapid star formation, known
    as starbursts, and rapid growth of a single super-massive black hole
    in each galactic centre. A popular paradigm for such evolution has
    the black holes growing mostly in obscurity, buried deep within the
    dusty gas in the centres of the galaxies. Those are rich star-forming
    galaxies, until a blowout of gas and dust (outflow) extinguishes the
    star formation and halts further growth in the black holes. At that
    stage there is revealed the luminous material in the immediate
    vicinity of the rapidly growing black hole in the galactic nucleus.
    Such objects are known as quasars. Quasars can eject material at
    high speeds, possibly helping to drive the blowout and regulate star
    formation in their host galaxies. However, many aspects of that
    evolutionary scheme are not understood. Quasars that are partially
    obscured by dust, which reddens their light in a way that is similar
    to the apparent reddening of the Sun as it approaches sunset on
    Earth, might provide windows into galactic evolution during the brief
    transition stage when the starburst is winding down and the visibly
    luminous quasar is first being revealed in the galactic centre. New
    research describes the discovery of the new population of extremely
    red quasars detected in the Baryon Oscillation Sky Survey (BOSS) of
    the Sloan Digital Sky Survey (SDSS).
    The main goal of that study was to determine the size of the
    population of extremely red quasars, and to characterize its basic
    properties in comparison with the much larger population of quasars
    in the BOSS–SDSS survey overall. The extremely red quasars were
    selected for study because of their extreme colour, but the analysis
    reveal a number of peculiar properties consistent with a unique and
    possibly young evolutionary stage. In particular, they have an
    exceptionally high incidence of powerful quasar-driven outflows that
    could be involved in galaxy-wide blowouts of gas and dust. Overall,
    the gaseous environments around the black holes appear to be more
    extended and more energetic than the environments of normal quasars,
    which might occur at specific times when young gas-rich host galaxies
    are dumping prodigious amounts of matter into the central black holes,
    creating an extreme variety of quasars. More work is needed now to
    examine the population of extremely red quasars further and understand
    its relationship to the general phenomenon of quasars and, perhaps, to
    a particularly violent phase of quasar-galaxy evolution.

    University of California at Riverside

    A team of researchers has found a large population of distant dwarf
    galaxies that could reveal important details about a productive period
    of star formation in the Universe thousands of millions of years ago.
    The findings build on a growing body of knowledge about dwarf
    galaxies, the smallest and dimmest galaxies in the Universe. Though
    relatively diminutive, they are very important for understanding the
    history of the Universe. It is believed that dwarf galaxies played a
    significant role during the 're-ionization era', in transforming the
    early Universe from being dark, neutral and opaque to one that is
    bright, ionized and transparent. Despite their importance, distant
    dwarf galaxies remain elusive, because they are extremely faint and
    mostly beyond the reach of even the best telescopes, so the current
    picture of the early Universe is incomplete. However, gravitational
    lensing, which was predicted by Einstein from his general theory of
    relativity long before it was actually observed, causes a massive
    object such as a galaxy located along the line of sight to another
    distant object to act as a natural lens, concentrating the light
    coming from the background source. The phenomenon sometimes allows
    us to discover distant dwarf galaxies that would otherwise be too
    faint to detect.
    As a proof of concept, in 2014 the team targeted one cluster of
    galaxies that produces the gravitational-lensing effect and got a
    glimpse of what appeared to be a large population of distant dwarf
    galaxies. The team used the Wide-Field Camera 3 on the Hubble Space
    Telescope to take deep images of three clusters of galaxies. They
    found the large population of distant dwarf galaxies from a time when
    the Universe was between two and six thousand million years old.
    That cosmic time is critical, as it was the most productive time
    for star formation in the Universe. In addition, the team obtained
    spectroscopic data from the Multi-Object Spectrograph for Infrared
    Exploration (MOSFIRE) on the Keck telescope, and confirmed that the
    galaxies belonged to that important cosmic period. Those dwarf
    galaxies are 10 to 100 times fainter than galaxies that had been
    previously observed from that period of time. Though faint, the
    galaxies are far more numerous than their brighter counterparts.
    The study demonstrates that the number of dwarf galaxies changed
    during that important time period in such a way that they were
    even more abundant at earlier times. In fact, the researchers had
    unveiled a population of dwarf galaxies that were the most numerous
    galaxies in the Universe during those times. Despite their individual
    faintness, the dwarf galaxies produced more than half of all ultra-
    violet light during that era. As ultraviolet radiation is produced
    by young hot stars, dwarf galaxies evidently hosted a significant
    fraction of newly-formed stars at that period of cosmic time. Those
    results suggest that dwarf galaxies played a prominent role in the
    re-ionization era; they will be among the primary targets of the next
    generation of telescopes, particularly the James Webb Space Telescope,
    scheduled to be launched in 2018.

    BBC Online

    Europe's and Russia's new satellite at Mars has sent back its first
    images of the planet. The Trace Gas Orbiter (TGO) arrived on October
    19, putting itself into a highly eccentric elliptical parking orbit,
    which must be circularized over the coming year before the mission
    can become fully operational. Scientists have, however, taken the
    opportunity of some close passes to the planet in recent days to check
    out the TGO's instrumentation. They are delighted at the quality of
    the pictures returned from the camera system, CaSSIS (the Colour and
    Stereo Surface Imaging System). Two of TGO's sensors – NOMAD and ACS
    – also came through their early tests. Those are the sensors that
    will make a detailed inventory of Mars' atmospheric gases. In
    particular, they will go after the components that constitute less
    than 1% of the planet's air — chemical species such as methane, water
    vapour, nitrogen dioxide, and sulphur dioxide. Methane is the main
    focus. From previous measurements, its concentration seems to be low
    and sporadic in nature, but the mere fact that it is detected at all
    is really fascinating.
    Methane (CH4) is the simplest organic molecule, and ought to be
    destroyed easily in the harsh Martian environment, so its persistence
    — and the occasional spikes in its signal — indicate a source that
    replenishes the gas. The speculation is that it could be coming from
    microbial life somewhere on the planet. It will be CaSSIS's job to
    look for possible topographical forms on the surface that might tie
    into methane sources. A fourth instrument, FREND, will sense hydrogen
    in the near-surface. Those data can be used as proxy for the presence
    of water or hydrated minerals. That again is information that could
    yield answers to the methane question. TGO was the unspoken success
    on the day that ESA's Schiaparelli lander crashed onto Mars. The
    surface probe had been dropped off by TGO and was making its ill-fated
    descent just as the satellite took up its parking orbit, and the
    successful insertion went almost unnoticed in the fuss over
    Schiaparelli. TGO is the first phase in a joint venture at Mars that
    Europe is undertaking with Russia. The second step in the project,
    known as ExoMars, is to put a robot rover on the planet in 2021. It
    needs a lot of money from the European side to go forward, however —
    just over 400m Euros. Research ministers from ESA member states are
    meeting this week in Switzerland to try to resolve the budget problem.

    Bulletin compiled by Clive Down
    (c) 2016 The Society for Popular Astronomy
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