The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 439 2017 February

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    Electronic News Bulletin No. 439 2017 February 5

    Here is the latest round-up of news from the Society for Popular
    Astronomy. The SPA is arguably Britain's liveliest astronomical
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    Paulson School of Engineering and Applied Sciences, Harvard
    The presence of water on ancient Mars is a paradox. There's plenty of
    areographical evidence that rivers periodically flowed across the planet's
    surface. Yet in the period of time when those waters are supposed to
    have run — three to four billion years ago — Mars should have been too
    cold to support liquid water. Researchers suggest that early Mars may
    have been warmed intermittently by a powerful greenhouse effect. They
    found that interactions between methane, carbon dioxide and hydrogen
    in the early Martian atmosphere may have created warm periods when the
    planet could support liquid water on the surface. Early Mars is
    unique in the sense that it is the one planetary environment, other
    than the Earth, where we can say with confidence that there were at
    least episodic periods when life could have flourished. If we under-
    stood how early Mars operated, it could tell us something about the
    potential for finding life on other planets outside the Solar System.
    Four billion years ago, the Sun was about 30% fainter than it is today
    and significantly less solar radiation — a.k.a. heat — reached the
    Martian surface. The radiation that did reach the planet was trapped
    by the atmosphere, resulting in warm, wet periods. For decades,
    researchers have struggled to model exactly how the planet was
    insulated. The obvious culprit is CO2. Carbon dioxide makes up 95%
    of today's Martian atmosphere and is the best-known and most abundant
    greenhouse gas on the Earth.
    There must have been something else in Mars' atmosphere that
    contributed to a greenhouse effect. The atmospheres of rocky planets
    lose lighter gases, such as hydrogen, to space over time. (In fact,
    the oxidation that gives Mars its distinctive hue is a direct result
    of the loss of hydrogen.) The team looked to those long-lost gases —
    known as reducing gases — to provide a possible explanation for Mars'
    early climate. In particular, the team looked at methane, which today
    is not abundant in the Martian atmosphere. Billions of years ago, however,
    areological processes could have been releasing significantly more
    methane into the atmosphere. That methane would have been slowly
    converted to hydrogen and other gases, in a process similar to that
    occurring today on Saturn's moon Titan. To understand how that early
    Martian atmosphere may have behaved, the team needed to understand
    the fundamental properties of those molecules. In 1977, Carl Sagan first
    speculated that hydrogen warming could have been important on early
    Mars, but it is only now that scientists have been able to calculate its
    greenhouse effect at all accurately. It is also the first time that methane
    has been shown to be an effective greenhouse gas on early Mars. This
    research shows that the warming effects of both methane and hydrogen
    have been underestimated in the past by a significant amount. The
    researchers discovered that methane and hydrogen, and their inter-
    action with carbon dioxide, were much better at warming early Mars
    than had previously been believed. One of the reasons that early Mars
    is so fascinating is that life needs complex chemistry to emerge.
    Episodes of the emission of reducing gas, followed by planetary
    oxidation, could have created favourable conditions for life on Mars.

    The Hebrew University of Jerusalem

    Although we can't feel it, we are in constant motion: the Earth spins
    on its axis at about 1,600 km/h; it orbits around the Sun at about
    100,000 km/h; the Sun orbits our Milky Way galaxy at about 850,000
    km/h; and the Milky Way galaxy and its companion galaxy Andromeda are
    moving with respect to the expanding Universe at roughly 2 million
    km/h. But what is propelling the Milky Way's race through space?
    Until now, scientists assumed that a dense region of the Universe is
    pulling us towards it, in the same way that gravity made Newton's
    apple fall to the ground. The initial 'prime suspect' was called the
    Great Attractor, a region of half a dozen rich clusters of galaxies
    150 million light-years from the Milky Way. Soon after, attention was
    drawn to an area of more than two dozen rich clusters, called the
    Shapley Concentration, which sits 600 million light-years beyond the
    Great Attractor. Now researchers report that our Galaxy is not only
    being pulled, but also pushed. In a new study, astronomers describe a
    previously unknown, very large, empty region in our extragalactic
    neighbourhood. Largely devoid of galaxies, that void exerts what could
    be looked upon as a repelling force on our Local Group of galaxies.
    By 3-d mapping the flow of galaxies through space, the researchers
    found that our Milky Way galaxy is speeding away from a large,
    previously unidentified region of low density. Because it repels
    rather than attracts, they call this region the Dipole Repeller.
    In addition to being pulled towards the known Shapley Concentration,
    we are also being pushed away from the newly discovered Dipole
    Repeller. Thus it has become apparent that push and pull are of
    comparable importance at our location.
    The presence of such a low-density region has been suggested
    previously, but confirming the absence of galaxies by observation has
    proved challenging. But in the new study, researchers tried a
    different approach. Using powerful telescopes, among them the Hubble
    space telescope, they constructed a 3-dimensional map of the galaxy
    flow field. Flows are direct responses to the distribution of matter,
    away from regions that are relatively empty and toward regions of mass
    concentration; the large-scale structure of the Universe is encoded in
    the flow field of galaxies. They studied the peculiar velocities —
    those in excess of the Universe's rate of expansion — of galaxies
    around the Milky Way, combining different data sets of peculiar
    velocities with a rigorous statistical analysis of their properties.
    They thereby inferred the underlying mass distribution that consists
    of dark matter and luminous galaxies — over-dense regions that
    attract and under-dense ones whose attraction is less and so seem to
    repel. By identifying the Dipole Repeller, the researchers were able
    to reconcile both the direction of the Milky Way's motion and its
    magnitude. They expect that future ultra-sensitive surveys at optical,
    near-infrared and radio wave-lengths will identify the few galaxies
    expected to lie in the void, and directly confirm the existence of
    that void associated with the Dipole Repeller.

    National Radio Astronomy Observatory

    Dwarf galaxies, nuggets of stars and gas 100 to 1,000 times smaller
    than the Milky Way, are thought to be the building blocks of massive
    galaxies. Evidence for groups of merging dwarf galaxies, however, has
    been lacking until now. Using data from the Sloan Digital Sky Survey
    (SDSS) and various optical telescopes, a team of astronomers has
    discovered seven distinct groups of dwarf galaxies with just the right
    starting conditions to merge eventually and form larger galaxies,
    including spiral galaxies like the Milky Way. That discovery offers
    compelling evidence that the mature galaxies we see in the Universe
    today were formed when smaller galaxies merged many (U.S.)billions of
    years ago. Astronomers know that to make a large galaxy, the Universe
    has to bring together many smaller galaxies. For the first time, they
    have found examples of the first steps in this process — entire
    populations of dwarf galaxies that are all bound together in the same
    general neighbourhoods. The team began its search by poring over SDSS
    data looking for pairs of interacting dwarf galaxies. It next
    examined the images to find specific pairs that appeared to be part of
    even larger assemblages of similar galaxies. The researchers then used
    the Magellan telescope in Chile, the Apache Point Observatory in New
    Mexico, and the Gemini telescope in Hawaii to confirm that the
    apparent clusters are not just in the same line of sight but are also
    approximately the same distance away, indicating that they are gravi-
    tationally bound together. The team hopes that that discovery will
    encourage future studies of groups of dwarf galaxies and offer insights
    into the formation of galaxies like the Milky Way.


    By using galaxies as giant gravitational lenses, an international
    group of astronomers using the Hubble space telescope has made an
    independent measurement of how fast the Universe is expanding. The
    newly measured expansion rate for the local Universe is consistent
    with earlier findings. Those are, however, in intriguing disagreement
    with measurements of the early Universe, that hints at a fundamental
    problem at the very heart of our understanding of the cosmos. The
    Hubble constant — the rate at which the Universe is expanding — is
    one of the fundamental quantities describing our Universe. A group of
    astronomers from the H0LiCOW collaboration used the Hubble telescope
    and other telescopes, in space and on the ground, to observe five
    galaxies in order to arrive at an independent measurement of the
    Hubble constant. The new measurement is completely independent of,
    but in excellent agreement with, other measurements of the Hubble
    constant in the local Universe that used Cepheid variable stars and
    supernovae as points of reference. However, the value obtained by the
    team, as well as the values from Cepheids and supernovae, differ from
    the measurement made by the Planck satellite. But there is an
    important distinction — Planck measured the Hubble constant for the
    early Universe by observing the cosmic microwave background. While
    the value for the Hubble constant determined by Planck fits with our
    current understanding of the cosmos, the values obtained by the
    various groups of astronomers for the local Universe disagree with
    the accepted theoretical model of the Universe. The expansion rate
    of the Universe is now starting to be measured in different ways with
    such high precision that actual discrepancies may possibly point
    towards new physics beyond our current knowledge of the Universe.

    The targets of the study were massive galaxies positioned between the
    Earth and very distant quasars. The light from the more distant
    quasars is bent around the huge masses of the galaxies as a result of
    strong gravitational lensing. That creates multiple images of the
    background quasar, some of them smeared into extended arcs. Because
    galaxies do not create perfectly spherical distortions in the fabric
    of space and the lensing galaxies and quasars are not perfectly
    aligned, the light that forms the different images of the background
    quasar follows paths which have slightly different lengths. Since
    the brightness of quasars changes over time, astronomers can see the
    different images flicker at different times; the delays between them
    depend on the lengths of the paths that the light has taken. The
    delays are directly related to the value of the Hubble constant.
    That method is the simplest and most direct way to measure the Hubble
    constant, as it uses only geometry and General Relativity, no other
    assumptions. Use of the accurate measurements of the time delays
    between the multiple images, as well as computer models, has allowed
    the team to determine the Hubble constant to a rather high precision,
    3.8%. The Hubble constant is crucial for modern astronomy as it can
    help to confirm or refute whether our picture of the Universe —
    composed of dark energy, dark matter and normal matter — is actually
    correct, or if we are missing something fundamental.


    A simple chemical method could greatly enhance how scientists search
    for signs of life on other planets. The test uses a liquid-based
    technique known as capillary electrophoresis to separate a mixture of
    organic molecules into its components. It was designed specifically
    to look for amino acids, the structural building blocks of all life on
    Earth. The method is 10,000 times more sensitive than current methods
    employed by spacecraft like the Mars Curiosity rover, according to a
    new study carried out by researchers from the JPL in Pasadena. One of
    the key advantages of the new way of using capillary electrophoresis
    is that the process is relatively simple and easy to automate for the
    liquid samples expected on ocean-world missions: it involves combining
    a liquid sample with a liquid reagent, followed by chemical analysis
    under conditions determined by the team. By shining a laser across
    the mixture — a process known as laser-induced fluorescence detection
    — specific molecules can be observed moving at different speeds.
    They get separated on the basis of how quickly they respond to
    electric fields. While capillary electrophoresis has been known since
    the early 1980s, this is the first time that it has been tailored
    specifically to detect extra-terrestrial life on an ocean world.
    The method improves on previous attempts by increasing the number of
    amino acids that can be detected in a single run. Additionally, it
    allows scientists to detect the amino acids at very low concentra-
    tions, even in very salty samples, with a very simple 'mix and analyze'
    The researchers used the technique to analyze amino acids present in
    the salt-rich waters of Mono Lake in California. The lake's excep-
    tionally high alkaline content makes it a challenging habitat for
    life, and an excellent stand-in for salty waters believed to be on
    Mars, or the ocean worlds of Saturn's moon Enceladus and Jupiter's
    moon Europa. The researchers were able simultaneously to analyze 17
    different amino acids, which they are calling 'the Signature 17
    standard'. Those amino acids were chosen for study because they are
    the ones most commonly found on the Earth or elsewhere. Using that
    method, it is possible to distinguish between amino acids that come
    from non-living sources like meteorites and those that come from
    living organisms. The key to detecting amino acids related to life is
    an aspect known as chirality. Chiral molecules such as amino acids
    come in two forms that are mirror images of one another. Although
    amino acids from non-living sources contain approximately equal
    amounts of the 'left'- and 'right'-handed forms, amino acids from
    living organisms on Earth are almost exclusively the 'left-handed'
    form. It is expected that amino-acid life elsewhere would also need
    to 'choose' one of the two forms in order to create the structures of
    life. For that reason, chirality of amino acids is considered one of
    the most powerful signatures of life. One of NASA's highest-level
    objectives is the search for life in the Universe. Our best chance of
    finding life on worlds physically accessible by spacecraft may lie in
    the use of powerful liquid-based analyses like the one tried on Mono


    A new device on the Keck Telescope in Hawaii has delivered its first
    images, showing a ring of planet-forming dust around a star, and
    separately, a brown dwarf (a cool, star-like body), lying near its
    companion star. The device, called a vortex coronagraph, was recently
    installed inside NIRC2 (Near Infrared Camera 2), the workhorse
    infrared imaging camera at Keck. It can image planetary systems and
    brown dwarfs closer to their host stars than any other instrument in
    the world. The vortex study has obtained the first direct image of
    the brown dwarf called HIP 79124 B. That brown dwarf is located 23
    astronomical units from a star in a nearby star-forming region called
    Scorpio-Centaurus. The ability to image objects that are very close
    to stars also allows astronomers to search for planets around more
    distant stars, where the planets and stars would appear closer
    together. Being able to survey distant stars for planets is important
    for catching planets still forming. The second vortex study presents
    an image of the innermost of three rings of dusty, planet-forming
    material around a young star called HD 141569 A. The results, when
    combined with infrared data from the Spitzer, WISE, and Herschel
    missions, reveal that the star's planet-forming material is made up of
    pebble-size grains of olivine, one of the most abundant silicates in
    the Earth's mantle. The data also show that the temperature of the
    innermost ring imaged by the vortex is about 100 degrees K, slightly
    less cold than our asteroid belt.
    Bulletin compiled by Clive Down
    (c) 2017 The Society for Popular Astronomy

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