The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 432 October 25th

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    Electronic News Bulletin No. 432 2016 October 23

    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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    Planetary Science Institute

    New research shows that outbursts of comet nuclei are probably caused
    by surface avalanches rather than geyser-like eruptions from within.
    Rapid asymmetric brightening events of comets have been observed for
    decades and have long been thought to be the result of some sort of
    eruption of materials from deep within the interior of a comet.
    High-resolution images from Rosetta observations of 67P/Churyumov-
    Gerasimenko show outbursts that resemble plumes of material from
    geysers on Earth. However, there is a major problem with that model.
    There is no internal heat source on comets to power geyser-like
    eruptions. Instead, outburst plumes are to be seen as the natural
    result of avalanches. The surfaces of comets have regions at the
    bases of slopes and cliffs that are rich in icy materials, and are
    actively sublimating, with ice turning directly into gas. As the gas
    leaves the surface of the comet, it produced a weak breeze. When
    granular materials on comets slide downslope or over a cliff, they
    enter this sublimation breeze and are blown into a tightly collimated
    plume of material that leaves the surface of the nucleus. This model
    is consistent with data collected by the Rosetta spacecraft, and
    provides a physical mechanism that allows the outbursts to be studied
    to determine where on the surface they come from and how much material
    avalanched downslope.

    Royal Observatory of Belgium
    New data from the Cassini mis
    sion to Saturn reveal that a sub-surface
    ocean lies deep within Saturn's moon Dione. Two other moons of
    Saturn, Titan and Enceladus, are already known to hide global oceans
    beneath their icy crusts. In the new study, researchers of the Royal
    Observatory of Belgium show that gravity data from recent Cassini
    fly-bys can be explained if Dione's crust floats on an ocean 100 km
    below the surface. The ocean is several tens of kilometres deep and
    surrounds a large rocky core. Seen from within, Dione is very similar
    to its smaller but more famous neighbour Enceladus, whose south-polar
    region spurts huge jets of water vapour into space. Dione seems to be
    quiet now, but its broken surface bears witness to a tumultuous past.
    According to the new study, Enceladus' ocean is much closer to the
    surface, especially near the south pole where geysers erupt through a
    few kilometres of crust. These findings agree well with the discovery
    last year by Cassini that Enceladus undergoes large oscillations,
    called libration, during its orbit. Enceladus' libration would be
    much smaller if its crust were thicker. As for Dione, the new study
    finds that it harbours a deep ocean between its crust and core.
    Dione's ocean has probably survived for the whole history of the moon.

    University of Idaho

    After re-examining data acquired by the Voyager 2 spacecraft,
    astronomers have detected wavy patterns in two of Uranus's rings —
    patterns that may be indicative of two undiscovered moons. Like the
    other gas giants in the Solar System, Uranus has a ring system, though
    it is not nearly as spectacular as the one around Saturn. And like
    the other gas giants, Uranus has a lot of natural satellites — 27 are
    now known. New research suggests that that number might have to be
    revised; data collected by Voyager 2 during its historic 1986 fly-by
    hint at two undiscovered moons lurking near a pair of Uranus rings.
    The suspected new moons reside in Alpha and Beta — the 5th and 6th
    rings. Voyager 2 found 10 moons when it visited the planet in 1986,
    tripling the number of moons known to orbit the gas giant. The two
    rings exhibit a series of wavy patterns consistent with the presence
    of two tiny moons. The patterns may be wakes from small moonlets
    orbiting outside those rings. Importantly, the observations are
    consistent with how Uranus's other moons, such as Cordelia and
    Ophelia, are exerting gravitational pressure on the dust, rocks, and
    ice within the rings, herding the particles along a narrow formation.
    If the now-postulated moons exist, they are quite dark and small,
    measuring only 4 to 14 km across. That would make them smaller than
    any other known moons orbiting the planet, which explains why Voyager
    2 did not detect them directly. The researchers are now planning to
    inspect Uranus with the Hubble telescope.

    NASA/Jet Propulsion Laboratory

    The Hubble telescope has detected super-hot blobs of gas, each twice
    as massive as the planet Mars, being ejected near a dying star. The
    plasma balls are moving so fast that it would take only half an hour
    for them to travel the distance between the Earth and the Moon.
    Astronomers estimate that such stellar 'cannon fire' has taken place
    every 8.5 years for at least the past 400 years. The fireballs
    present a puzzle to astronomers, because the ejected material could
    not have been shot out by the host star, called V Hydrae. The star is
    a bloated red giant, 1,200 light-years away, which has probably shed
    at least half its mass into space during its death throes. Red giants
    are dying stars in the late stages of their existence, that are
    exhausting the nuclear fuel that makes them shine. They have expanded
    in size and are shedding their outer layers into space. The current
    best explanation suggests that the plasma balls were launched by an
    unseen companion star. According to that theory, the companion would
    have to be in an elliptical orbit that carries it close to the red
    giant's puffed-up atmosphere every 8.5 years. As the companion enters
    the bloated star's outer atmosphere, it steals material, which then
    settles into a disc around the companion and serves as the launching
    pad for blobs of plasma, which travel at roughly half a million miles
    per hour. This star system could be the archetype to explain the
    variety of glowing shapes called planetary nebulae, uncovered by
    Hubble, that are seen around dying stars. They are expanding shells
    of glowing gas expelled by stars late in their evolution..
    Hubble observations over the past two decades have revealed an
    enormous complexity and diversity of structure in planetary nebulae.
    The telescope has imaged knots of material in the glowing gas clouds
    surrounding the dying stars. Astronomers speculated that the knots
    were actually jets ejected by discs of material around companion stars
    that were not visible in the Hubble images (many stars in our Milky
    Way galaxy are members of binary systems). But the details of how the
    jets were produced remained a mystery. Astronomers want to identify
    the process that causes the transformation from a puffed-up red giant
    to a beautiful, glowing planetary nebula: dramatic changes occur over
    roughly 200 to 1,000 years, which is the blink of an eye in cosmic
    time. The team used Hubble's 'Space Telescope Imaging Spectrograph'
    (STIS) to conduct observations of V Hydrae and its surrounding region
    over an 11-year period, first from 2002 to 2004, and then from 2011 to
    2013. The data showed a string of monstrous, super-hot blobs, each
    with a temperature of more than 9,400°C — almost twice as hot as the
    surface of the Sun. The researchers compiled a detailed map of the
    blobs' locations, allowing them to trace the first clumps back to
    1986. The STIS data show blobs that have just been ejected, blobs
    that have moved a little farther away, and blobs that are even farther
    away. STIS detected the giant structures as far away as 37000 million
    miles away from V Hydrae, more than eight times further away than the
    Kuiper Belt of icy debris at the edge of our Solar System is from the
    Sun. The blobs expand and cool as they move further away, and are
    then not detectable in visible light. But observations taken at
    longer, sub-millimetre wavelengths in 2004, by the Sub-millimetre
    Array in Hawaii, revealed fuzzy, knotty structures that may be blobs
    launched 400 years ago.
    A surprise from the STIS observation was that the disc does not fire
    the monster clumps in exactly the same direction every 8.5 years. The
    direction flip-flops slightly, from side-to-side to back-and-forth,
    owing to a possible wobble in the accretion disc. Astronomers have
    noted that V Hydrae is obscured every 17 years, as if something is
    blocking its light. Astronomers suggest that owing to the back-and-
    forth wobble of the jet direction, the blobs alternate between passing
    behind and in front of V Hydrae. When a blob passes in front of the
    star, it shields the red giant from view. The team hopes to use Hubble
    to conduct further observations of the V Hydrae system, including the
    most recent blob ejected in 2011. The astronomers also plan to use
    the Atacama array (ALMA) in Chile to study blobs launched over the
    past few hundred years that are now too cool to be observed by Hubble.

    York University

    Planets that revolve around two suns may surprisingly survive the
    violent late stages of the stars' lives, according to new research.
    The finding is surprising, because planets orbiting close to a single
    sun, like Mercury and Venus in our Solar System, would be destroyed
    when the ageing star swells into a red giant. The study found that
    planets orbiting binary stars — also referred to as circum-binary
    planets or “Tatooine worlds” — often escape destruction by moving out
    to larger orbits. That is very different from what will happen in our
    own Solar System a few thousand million years from now, when the Sun
    starts to evolve and expand to such a size that it will engulf Mercury
    and Venus and possibly the Earth too, faster than they can migrate out
    to larger orbits. It seems that if we had a second star in the centre
    of our Solar System, things might go differently. Binary-star systems
    are common, and if the two stars are close enough to one another, when
    one starts evolving and expanding into a giant, they exchange material
    and spiral towards each other, resulting in their sharing a common
    atmosphere (also called a common envelope). The binary-star system
    ends up losing a large amount of mass, or might be destroyed in a
    supernova explosion. The team found that the planets will mostly
    survive the common-envelope phase — even those orbiting very close to
    their stars. In addition, the planets can migrate to larger orbits,
    analogous to what it would be like if Venus moved out to where Uranus
    orbits the Sun. In some cases, planets can even reach more than twice
    the distance to Pluto. Interestingly, when there are multiple planets
    orbiting a binary star, some can be ejected from the system, while
    others can switch places or even collide with their stars. The
    reconfiguration can be quite dramatic when there are several planets.
    Although all of the known circum-binary planets are gas giants, it is
    possible that, somewhere, there is a terrestrial circum-binary planet
    that migrates to an orbit that now makes the planet potentially
    habitable for a time.


    Astronomers using the infrared VISTA telescope have for the first time
    discovered ancient stars, of the type known as RR Lyrae, in the centre
    of the Milky Way. RR Lyrae stars typically reside in ancient stellar
    populations over 10,000 million years old. Their discovery suggests
    that the bulging centre of the Milky Way probably grew through the
    merging of primordial star clusters. The stars may even be the
    remains of the most massive and oldest surviving star cluster of the
    entire Milky Way. Our Milky Way has a densely populated centre — a
    feature common to many galaxies, but ours is the only one close enough
    to study in detail. The discovery of RR Lyrae stars provides evidence
    that helps astronomers to decide between two main competing theories
    for how nuclear bulges form. RR Lyrae stars are typically found in
    dense globular clusters. They are variable stars, and the brightness
    of each RR Lyrae star fluctuates regularly. By observing the length
    of each cycle of brightening and dimming in an RR Lyrae, and also
    measuring the star's brightness, astronomers can calculate its
    distance. Unfortunately, these excellent distance-indicator stars are
    frequently outshone by younger, brighter stars and in some regions
    they are hidden by dust. Therefore, locating RR Lyrae stars right in
    the extremely crowded heart of the Milky Way was not possible until
    the public VVV survey was carried out using infrared light. Even so,
    the team described the task of locating the RR Lyrae stars in amongst
    the crowded throng of brighter stars as 'daunting'. Its hard work was
    rewarded, however, with the identification of a dozen RR Lyrae stars.
    The discovery indicates that remnants of ancient globular clusters are
    scattered within the centre of the Milky Way's bulge. The theory that
    galactic nuclear bulges form through the merging of globular clusters
    is contested by the competing hypothesis that the bulges are actually
    due to the rapid accretion of gas.

    An international team of astronomers has found that the Universe
    contains at least two trillion galaxies, ten times more than previously
    thought. Astronomers have long sought to determine how many galaxies
    there are in the observable Universe, the part of the cosmos where
    light from distant objects has had time to reach us. Over the last 20
    years scientists have used images from the Hubble telescope to
    estimate that the Universe we can see contains around 100-200
    billion galaxies. Current astronomical technology allows us to study
    just 10% of these galaxies, and the remaining 90% will be seen only
    when bigger and better telescopes are developed (if then). The team
    began by performing the initial galaxy-counting analysis, work which
    was crucial for establishing the feasibility of the larger-scale
    study. The team then converted pencil-beam images of deep space from
    telescopes around the world, and especially from the Hubble telescope,
    into 3-D maps. Those allowed astronomers to calculate the density of
    galaxies as well as the volume of one small region of space after
    another. That enabled the team to establish how many galaxies we have
    missed — much like an intergalactic archaeological dig. The results
    of the study are based on the measurements of the number of observed
    galaxies at different epochs through the Universe's history. When the
    team examined how many galaxies there were at a given epoch it found
    that there were significantly more at earlier times.
    It appears that when the Universe was 'only' a few billion
    years old there were ten times as many galaxies in a given volume of
    space as there are within a similar volume today. Most of those
    galaxies were low-mass systems with masses similar to those of the
    satellite galaxies surrounding the Milky Way. That is very surprising
    as we know that, over the 13.7 billion years of cosmic evolution
    since the Big Bang, galaxies have been growing through star formation
    and mergers with other galaxies. Finding more galaxies in the past
    implies that significant evolution must have occurred to reduce their
    number through extensive merging of systems. We are missing the vast
    majority of galaxies because they are very faint and far away. The
    number of galaxies in the Universe is a fundamental question in
    astronomy, and it is astonishing that over 90% of the galaxies in the
    cosmos have yet to be studied.

    University of California, Irvine

    Will astronauts travelling to Mars remember much of it? Scientists
    have found that exposure to highly energetic charged particles — much
    like those found in the Galactic cosmic rays that will bombard astro-
    nauts during extended space flights — causes significant long-term
    brain damage in test rodents, resulting in cognitive impairments and
    dementia. The study follows one last year showing somewhat shorter-
    term brain effects of Galactic cosmic rays. For the new study,
    rodents were subjected to charged-particle irradiation (fully ionized
    oxygen and titanium) at the NASA Space Radiation Laboratory at New
    York's Brookhaven National Laboratory. Six months after exposure, the
    researchers still found significant levels of brain inflammation and
    damage to neurons. Imaging revealed that the brain's neural network
    was impaired through the reduction of dendrites and spines on the
    neurons, which disrupts the transmission of signals among brain cells.
    Those deficiencies were parallel to poor performance on behavioural
    tasks designed to test learning and memory. In addition, the team
    discovered that the radiation affected 'fear extinction', an active
    process in which the brain suppresses prior unpleasant and stressful
    associations, as when someone who nearly drowned learns to enjoy water
    again. Deficits in fear extinction could make one prone to anxiety,
    which could become problematic over the course of a three-year trip to
    and from Mars.
    Similar types of more severe cognitive dysfunction are common in
    brain-cancer patients who have received high-dose, photon-based
    radiation treatments. While dementia-like deficits in astronauts
    would take months to manifest, the time required for a mission to Mars
    is sufficient for such impairments to develop. People working for
    extended periods on the International Space Station, however, do not
    face the same level of bombardment with Galactic cosmic rays because
    they are still within the Earth's protective magnetosphere. Partial
    solutions are being explored. Spacecraft could be designed to include
    areas of increased shielding, such as those used for rest and sleep.
    However, the highly energetic charged particles will traverse the ship
    nonetheless and there is really no escaping them. Preventive treat-
    ments offer some hope. Researchers are working on pharmacological
    strategies involving compounds that scavenge free radicals and protect

    Bulletin compiled by Clive Down
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