The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 454 2017 Oct 8

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    The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 454 2017 October 8
    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
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    Europlanet Media Centre

    Lava tubes –underground caves created by volcanic activity — could
    provide protected habitats large enough to house streets on Mars or
    even towns on the Moon, according to research presented at the
    European Planetary Science Congress (EPSC) 2017 in Riga. A further
    study shows how the next generation of lunar orbiters will be able to
    use radar to locate such structures under the Moon's surface. Lava
    tubes can form in two ways. 'Overcrusted' tubes form when low-
    viscosity lava flows fairly close to the surface, developing a hard
    crust that thickens to create a roof above the moving lava stream.
    When the eruptions end, the conduit is drained, leaving a tunnel a few
    metres beneath the surface. 'Inflated' tubes are complex and deep
    structures that form when lava is injected into existing fissures
    between layers of rock or cavities from previous flows. The lava
    expands and leaves a huge network of connected galleries as it forces
    its way to the surface. Lava tubes are found in many volcanic areas
    on Earth, including Lanzarote, Hawaii, Iceland, North Queensland in
    Australia, Sicily, and the Galapagos islands. Underground networks of
    tubes can span up to 65 kilometres. Space missions have also observed
    chains of collapsed pits and 'skylights' on the Moon and Mars that
    have been interpreted as evidence of lava tubes. Recently the NASA
    GRAIL mission provided detailed gravity data for the Moon that
    suggested the presence of enormous sub-surface voids related to lava
    tubes below the lunar 'maria', plains of basalt formed in volcanic
    eruptions early in the Moon's history. Scientists have also presented
    a concept for a radar system specifically designed to detect lava
    tubes on the Moon from orbit. The radar will probe beneath the lunar
    surface with low-frequency electromagnetic waves and measure the
    reflected signals. Such a radar instrument could determine accurately
    the physical composition, size and shape of the caves and obtain a
    global map of their locations. The studies show that a multi-
    frequency sounding system is the best option for detecting lava tubes
    of very different dimensions. The simulations show that lava tubes
    have unique electromagnetic signatures, which can be detected from
    orbit irrespective of their orientation with respect to the radar
    movement direction. Therefore, an orbiter carrying such an instrument
    could make a crucial step towards finding safe habitats on the Moon
    for human colonisation.

    Brown University

    The scorching-hot surface of Mercury may seem an unlikely place to
    find ice, but research over the past 30 years has indicated that water
    is frozen there, hidden away on crater floors that are permanently
    shadowed from the Sun's blistering rays. Now, a new study suggests
    that there could be much more ice on Mercury's surface than previously
    thought. The study adds three new members to the list of craters
    near Mercury's north pole that appear to harbour large surface ice
    deposits. But in addition to those large deposits, the research also
    shows evidence that smaller-scale deposits are scattered around
    Mercury's north pole, both inside craters and in permanently shadowed
    areas between craters. Those deposits may be small, but they could
    add up to a lot of previously-unaccounted-for ice. The idea that
    Mercury might have frozen water emerged in the 1990s, when Earth-based
    radars detected highly reflective regions inside several craters near
    Mercury's poles. The planet's axis does not have much tilt, so its
    poles get little direct sunlight, and the floors of some craters get
    no direct sunlight at all. Without an atmosphere to hold in any heat
    from surrounding surfaces, temperatures in those eternal shadows have
    been calculated to be plenty low enough for water ice to be stable.
    That raised the possibility that the 'radar-bright' regions could be
    ice. That idea got a boost after NASA's MESSENGER probe entered an
    orbit around Mercury in 2011. The spacecraft detected neutron signals
    from the planet's north pole that were consistent with water ice.

    Tokyo Institute of Technology

    Exploration missions have suggested that Mars once had a warm climate,
    which sustained oceans on its surface. To keep Mars warm requires a
    dense atmosphere with a sufficient greenhouse effect, while at the
    present day Mars has a thin atmosphere whose surface pressure is only
    0.006 bar, resulting in the cold climate it has today. It has been a
    big mystery as to when and how Mars lost its dense atmosphere. An old
    meteorite has been known to contain a sample of the ancient Martian
    atmosphere. The researchers simulated how the composition of the
    Martian atmosphere might have changed throughout history under various
    conditions. By comparing the results to the isotopic composition of
    the trapped gas, the researchers revealed how dense the Martian
    atmosphere was at the time that the gas became trapped in the
    meteorite. The research team concluded that Mars had a dense
    atmosphere 4 billion years ago. The surface air pressure at the time
    was at least 0.5 bar and could have been much higher. Because Mars
    had a magnetic field about 4 billion years ago but subsequently lost
    it, the result suggests that stripping by the solar wind has been
    responsible for transforming Mars from a warm wet world into a cold
    desert one. NASA's MAVEN spacecraft is orbiting Mars to explore the
    processes that removed the Martian atmosphere. The Japan Aerospace
    Exploration Agency (JAXA) is also planning to observe the removal
    processes by the Martian Moons eXploration (MMX) spacecraft. Those
    missions may well reveal how the dense atmosphere predicted in this
    study to have existed on ancient Mars was removed over time.

    European Planetary Science Congress

    A fleet of tiny spacecraft could visit over 300 asteroids in just
    over three years, according to a mission study led by the Finnish
    Meteorological Institute. The Asteroid Touring Nanosat Fleet concept
    comprises 50 spacecraft propelled by innovative electric solar wind
    sails (E-sails) and equipped with instruments to take images and
    collect spectroscopic data on the composition of the asteroids. Each
    nanosat would visit six or seven asteroids before returning to Earth
    to deliver the data. In the mission scenario, the nanosats fly by
    their target asteroids at a range of around 1000 kilometres. Each
    nanosat carries a 4-centimetre telescope capable of imaging the
    surface of asteroids with a resolution of 100 metres or better. An
    infrared spectrometer analyses spectral signatures in light reflected
    or emitted by the asteroid to determine its mineralogy. The instru-
    ments can be pointed at the target by the use of two internal reaction
    wheels inside the nanosats. E-sails make use of the solar wind — a
    stream of electrically charged particles emitted from the Sun — to
    generate efficient propulsion without the need for any propellent.
    Thrust is generated by the slow rotation of a tether, attached at one
    end to a main spacecraft carrying an electron emitter and a high-
    voltage source and at the other to a small remote unit. The spinning
    tether completes a rotation in about 50 minutes, tracing out a broad,
    shallow cone around a centre of mass close to the main spacecraft.
    By altering its orientation in relation to the solar wind, the nanosat
    can change thrust and direction.


    The Hubble space telescope has photographed the most distant active
    inbound comet ever seen, currently beyond the orbit of Saturn.
    Slightly warmed by the remote Sun, it has already begun to develop an
    80,000-mile-wide coma, enveloping a tiny, solid nucleus of frozen gas
    and dust. The observations represent the earliest signs of activity
    ever seen from a comet entering the Solar System's planetary zone for
    the first time. The comet, called C/2017 K2 (PANSTARRS) or 'K2', has
    been travelling for millions of years from its home in the frigid
    outer reaches of the Solar System, where the temperature is about
    minus 262 degrees Centigrade. The comet's orbit indicates that it
    came from the Oort Cloud, a spherical region almost a light-year in
    diameter and thought to contain hundreds of billions of comets.
    Comets are the icy leftovers from the formation of the Solar System
    4.6 billion years ago and therefore pristine in icy composition.
    The Hubble observations of K2's coma suggest that sunlight is heating
    frozen volatile gases — such as oxygen, nitrogen, carbon dioxide, and
    carbon monoxide — that coat the comet's frigid surface. Those icy
    volatiles lift off from the comet and release dust, forming the coma.
    Past studies of the composition of comets near the Sun have revealed
    the same mixture of volatile ices. The volatiles are spread all
    through K2, and in the beginning, billions of years ago, they were
    probably all through every comet presently in the Oort Cloud. But the
    volatiles on the surface are the ones that absorb the heat from the
    Sun, so, in a sense, the comet is shedding its outer skin. Most
    comets are discovered much closer to the Sun, near Jupiter's orbit, so
    by the time we see them, the surface volatiles have already been baked
    off. That is why astronomers think that K2 is the most primitive
    comet ever seen.
    K2 was discovered in 2017 May by the Panoramic Survey Telescope and
    Rapid Response System (Pan-STARRS) in Hawaii, a survey project of
    NASA's Near-Earth Object Observations Program. Hubble revealed the
    extent of the coma and also helped to estimate the size of the nucleus
    — less than 12 miles across — though the tenuous coma is 10 Earth
    diameters across. That vast coma must have formed when the comet was
    even further away from the Sun. Digging through archival images,
    astronomers uncovered views of K2 and its fuzzy coma taken in 2013 by
    the Canada-France-Hawaii Telescope (CFHT) in Hawaii. But the object
    was then so faint that no one noticed it. It is likely that the comet
    has been continuously active for at least four years. In the CFHT
    data, K2 had a coma already, when it was at 2 billion miles from the
    Sun, between the orbits of Uranus and Neptune. As it approaches the
    Sun, it is getting warmer and warmer, and the activity is ramping up.
    But curiously, the Hubble images do not show any tail flowing from K2.
    The absence of such a feature indicates that the particles lifting off
    the comet are too large for radiation pressure from the Sun to sweep
    them back into a tail. Astronomers will have plenty of time to
    conduct detailed studies of K2. For the next five years, the comet
    will continue its journey into the inner Solar System before it
    reaches its closest approach to the Sun in 2022 just beyond Mars'
    orbit. The James Webb space telescope, an infrared observatory
    scheduled to be launched in 2018, could measure the heat from the
    nucleus, which would give astronomers a more accurate estimate of its

    ESA/Hubble Information Centre

    Astronomers have discovered that the well-studied exoplanet WASP-12b
    reflects almost no light, making it appear essentially pitch black.
    That discovery sheds new light on the atmospheric composition
    of the planet and also refutes previous hypotheses about WASP-12b's
    atmosphere. The results are also in stark contrast to observations of
    another similarly-sized exoplanet. The results are surprising, as
    the measured albedo of WASP-12b is 0.064 at most. That is an
    extremely low value, making the planet darker than fresh asphalt!
    It makes WASP-12b two times less reflective than our Moon, which has
    an albedo of 0.12. The low albedo shows that we still have a lot to
    learn about WASP-12b and other similar exoplanets. WASP-12b orbits
    the Sun-like star WASP-12A, about 1400 light-years away, and since its
    discovery in 2008 it has become one of the best-studied exoplanets.
    With a radius almost twice that of Jupiter and a year of just over one
    Earth day, WASP-12b is categorised as a 'hot Jupiter'. Because it is
    so close to its parent star, the gravitational pull of the star has
    stretched WASP-12b into an egg shape, and its heat has raised the
    surface temperature of the daylight side to 2600 degrees Celsius.
    The high temperature is also the most likely explanation for
    WASP-12b's low albedo. There are other hot Jupiters that have been
    found to be remarkably black, but they are much cooler than WASP-12b.
    For those planets, it is suggested that things like clouds and alkali
    metals are the reason for the absorption of light, but those don't
    work for WASP-12b because it is so incredibly hot. The daylight side
    of WASP-12b is so hot that clouds cannot form and alkali metals are
    ionized. It is even hot enough to break up hydrogen molecules into
    atomic hydrogen, which causes the atmosphere to act more like the
    atmosphere of a low-mass star than like a planetary atmosphere. That
    leads to the low albedo of the exoplanet. To measure the albedo of
    WASP-12b the scientists observed the exoplanet in 2016 October during
    an eclipse, when the planet was near full phase and passed behind its
    host star for a time. That is the best method to determine the albedo
    of an exoplanet, as it involves directly measuring the amount of light
    being reflected. However, that technique requires a precision ten
    times greater than traditional transit observations. Using Hubble's
    Space Telescope Imaging Spectrograph, the scientists were able to
    measure the albedo of WASP-12b at several different wavelengths.
    WASP-12b is only the second planet to have spectrally resolved albedo
    measurements, the first being HD 189733b, another hot Jupiter. The
    data allowed scientists to determine whether the planet reflects more
    light towards the blue or the red end of the spectrum. While the
    results for HD 189733b suggest that the exoplanet has a deep blue
    colour, WASP-12b, on the other hand, is not reflecting light at any
    wavelength. WASP-12b does, however, emit light because of its high
    temperature, giving it a red hue similar to hot glowing metal.

    Yale University

    The most-studied galaxy in the universe — the Milky Way — might not
    be as “typical” as previously thought, according to a new study. The
    Milky Way, which is home to the Earth and solar system, is host to
    several dozen smaller galaxy satellites. Those smaller galaxies orbit
    around the Milky Way and are useful in understanding the Milky Way
    itself. Early results from the Satellites Around Galactic Analogs
    (SAGA) survey indicate that the Milky Way's satellites are much more
    tranquil than other systems of comparable luminosity and environment.
    Many satellites of those 'sibling' galaxies are actively pumping out
    new stars, but the researchers found that the Milky Way's satellites
    are mostly inert. That is significant, according to the researchers,
    because many models for what we know about the universe rely on
    galaxies behaving in a fashion similar to the Milky Way. The SAGA
    survey began five years ago with a goal of studying the satellite
    galaxies around 100 Milky Way siblings. Thus far it has studied eight
    other Milky Way sibling systems, which the researchers say is too
    small a sample to come to any definitive conclusions. SAGA expects
    to study 25 Milky Way siblings in the next two years.

    National Science Foundation

    In August, detectors on two continents recorded gravitational-wave
    signals from a pair of black holes colliding. That discovery is the
    first observation of gravitational waves by three different detectors,
    marking a new era of greater insights and improved localization of
    cosmic events now available through globally networked gravitational-
    wave observatories. The collision was observed on Aug. 14 at 10:30:43
    UTC by two Laser Interferometer Gravitational-Wave Observatory (LIGO)
    detectors located in Louisiana and Washington, and the Virgo detector
    located in Italy. The collision is designated GW170814. The detected
    gravitational waves — ripples in space and time — were emitted
    during the final moments of the merger of two black holes, one with a
    mass about 31 times that of our Sun, the other about 25 times the mass
    of the Sun. The event, located about 1.8 billion light-years away,
    resulted in a spinning black hole with about 53 times the mass of our
    Sun — that means about three solar masses were converted into
    gravitational-wave energy during the coalescence. When an event is
    detected by a three-detector network, the area in the sky likely to
    contain the source shrinks significantly, improving distance accuracy.
    The sky region for GW170814 has a size of only 60 square degrees, more
    than 10 times smaller than the size using data available from the two
    LIGO interferometers alone. Being able to identify a smaller search
    region is important, because many compact-object mergers — for
    example those involving neutron stars — are expected to produce
    broadband electromagnetic emissions in addition to gravitational
    waves. The precise pointing information enabled 25 partner facilities
    to perform follow-up observations based on the LIGO-Virgo detection,
    but no counterpart was identified — as expected for black holes.

    Michigan Technological University

    Astronomers have definitively answered the question of whether cosmic
    particles emanate from outside the Milky Way Galaxy. Studying the
    distribution of the cosmic-ray arrival directions is the first step in
    determining where extragalactic particles originate. The collabor-
    ating scientists were able to make their recordings using the largest
    cosmic-ray observatory ever built, the Pierre Auger Observatory in
    Argentina, which involves more than 400 scientists from 18 countries.
    Scientists are now considerably closer to solving the mystery of where
    and how those extraordinary particles are created, a question of great
    interest to astrophysicists. Cosmic rays are the nuclei of elements
    from hydrogen to iron. Studying them gives scientists a way to study
    matter from outside our solar system — and now, outside our galaxy.
    Cosmic rays help us to understand the composition of galaxies and the
    processes that occur to accelerate the nuclei to nearly the speed of
    light. By studying cosmic rays, scientists may come to understand
    what mechanisms create the nuclei. Astronomer Carl Sagan once said,
    “The nitrogen in our DNA, the calcium in our teeth, the iron in our
    blood, the carbon in our apple pies, were made in the interiors of
    collapsing stars. We are made of starstuff.” To put it simply,
    understanding cosmic rays and where they originate can help us to
    answer fundamental questions about the origins of the Universe, our
    galaxy and ourselves.
    It is extremely rare for cosmic rays with energies greater than two
    joules to reach the Earth; the rate of their arrival at the top of
    the atmosphere is only about one per square kilometre per year, the
    equivalent to one cosmic ray hitting an area the size of a soccer
    field about once per century. A joule is a measure of energy; one
    joule is equivalent to one 3,600th of a watt-hour. When a single
    cosmic-ray particle hits the Earth's atmosphere, that energy is
    deposited within a few millionths of a second. Such rare particles
    are detectable because they create showers of electrons, photons and
    muons through successive interactions with the nuclei in the
    atmosphere. The showers spread out, sweeping through the atmosphere
    at the speed of light in a disc-like structure, like a giant
    dinner-plate, several kilometres in diameter. They contain more than
    10 billion particles. At the Pierre Auger Observatory, cosmic rays
    are detected by measuring the Cherenkov light — electromagnetic
    radiation emitted by charged particles passing through a medium, such
    as water, at greater than the phase velocity of light in that medium.
    The team measures the Cherenkov light produced in a detector, which is
    a large plastic structure that contains 12 tons of water. They pick
    up a signal in a few detectors within an array of 1,600 detectors.
    The detectors are spread over 3,000 square kilometres in western
    Argentina. The times of arrival of the particles at the detectors,
    measured with GPS receivers, are used to determine the direction from
    which the particles came within approximately one degree.
    By studying the distribution of the arrival directions of more than
    30,000 cosmic particles, the Auger Collaboration has discovered an
    anisotropy, which is the difference in the rate of cosmic-ray arrivals
    depending on which direction you look. That means that the cosmic
    rays do not come uniformly from all directions; there is a direction
    from which the rate is highest. The anisotropy is significant at
    5.2 standard deviations (a chance of about one in five million) in
    a direction where the distribution of galaxies is relatively high.
    Although that discovery clearly indicates an extragalactic origin for
    the particles, the specific sources of the cosmic rays are still
    unknown. The direction points to a broad area of sky rather than to
    specific sources, because even such energetic particles are deflected
    by a few tens of degrees in the magnetic field of our Galaxy. There
    have been cosmic rays observed with even higher energy those used in
    the Pierre Auger Collaboration study, some even with the kinetic
    energy of a well-struck tennis ball. As the deflections of such
    particles are expected to be smaller because of their higher energy,
    the arrival directions should point closer to their birthplaces. Such
    cosmic rays are even rarer, and further studies are under way to pin
    down which extragalactic objects are the sources. Knowledge of the
    nature of the particles will aid such identification, and continuing
    work on this problem is targeted in the upgrade of the Auger
    Observatory to be completed in 2018.


    Using data captured by ALMA in Chile and from the ROSINA instrument on
    ESA's Rosetta mission, a team of astronomers has found faint traces of
    the chemical compound Freon-40 — (CH3Cl), also known as methyl
    chloride and chloromethane, around both the infant star system IRAS
    16293-2422, about 400 light-years away, and the famous comet
    67P/Churyumov-Gerasimenko (67P/C-G) in our own Solar System. The new
    ALMA observation is the first detection ever of a stable organohalogen
    in interstellar space. Organohalogens consist of halogens, such as
    chlorine and fluorine, bonded with carbon and sometimes other
    elements. On Earth, such compounds are created by some biological
    processes — in organisms ranging from humans to fungi — as well as
    by industrial processes such as the production of dyes and medical
    drugs. The new discovery of one such compound, Freon-40, in places
    that must predate the origin of life, can be seen as a disappointment,
    as earlier research had suggested that such molecules could indicate
    the presence of life. Exoplanet research has gone beyond the point of
    finding planets — more than 3000 exoplanets are now known — to
    looking for chemical markers that might indicate the potential
    presence of life. A vital step is determining which molecules could
    indicate life, but establishing reliable markers remains a tricky
    process. ALMA's discovery of organohalogens in the interstellar
    medium also tells us something about the starting conditions for
    organic chemistry on planets. Such chemistry is an important step
    toward the origins of life. On the basis of this discovery, organo-
    halogens are likely to be a constituent of the so-called 'primordial
    soup', both on the young Earth and on nascent rocky exoplanets. That
    suggests that astronomers may have viewed things round the wrong way;
    rather than indicating the presence of existing life, organohalogens
    may be an important element in the little-understood chemistry
    involved in the origin of life.
    Using ALMA, astronomers have previously found precursors to sugars
    and amino acids around different stars. The additional discovery
    of Freon-40 around Comet 67P/C-G strengthens the links between the
    pre-biological chemistry of distant proto-stars and our own Solar
    System. The astronomers also compared the relative amounts of
    Freon-40 that contain different isotopes of chlorine in the infant
    star system and the comet — and found similar abundances. That
    supports the idea that a young planetary system can inherit the
    chemical composition of its parent star-forming cloud, and opens
    the possibility that organohalogens could arrive on planets in young
    systems during planet formation or via comet impacts. The results
    shows that we still have more to learn about the formation of
    organohalogens. Additional searches for organohalogens around other
    proto-stars and comets need to be undertaken to help find the answer.


    Observations of the Moon have revealed the final resting place of the
    European Space Agency's first lunar mission, SMART-1. The spacecraft
    was sent to a controlled impact with the lunar surface 11 years ago.
    Although an impact flash was imaged at the time by the Canada-France-
    Hawaii Telescope on the dark side of the boundary between night and
    day on the lunar surface, the exact location has not been identified
    until now. Scientists say that SMART-1 had a hard, grazing and
    bouncing landing at 2 km/s on the surface of the Moon. There were no
    other spacecraft in orbit at the time to give a close-up view of the
    impact, and finding the precise location became a 'cold case' for more
    than 10 years. For this 'crash scene investigation', scientists used
    all possible observational facts and computer models to identify the
    exact site and have finally found the scars. The next step will be
    to send a robotic investigator to examine the remains of the SMART-1
    spacecraft body and 'wings' of the solar arrays. The location is
    34°.262 south and 46°.193 west, consistent with the coordinates of
    impact calculated initially. The SMART-1 impact site was discovered
    from high-resolution images from NASA's Lunar Reconnaissance Orbiter
    (LRO). The images show a linear gouge in the surface, about 4 metres
    wide and 20 metres long, cutting across a small pre-existing crater.
    At the far end, a faint fan of ejecta sprays out to the south.

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

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