THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 475 2018 Sept 2

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    THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 475 2018 Sept 2
    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/

    STUDY SHOWS EARTH'S INGREDIENTS ARE NORMAL
    Goldschmidt Conference

    The Earth's building blocks seem to be built from 'pretty normal'
    ingredients, according to researchers working with the world's most powerful
    telescopes. Scientists have measured the compositions of 18 different
    planetary systems from up to 456 light-years away and compared them to ours,
    and found that many elements are present in similar proportions to those
    found on Earth. This is amongst the largest examinations to measure the
    general composition of materials in other planetary systems, and begins to
    allow scientists to draw more general conclusions on how they are forged,
    and what that might mean for finding Earth-like bodies elsewhere. The first
    planets orbiting other stars were not found until 1992 (the first one was
    orbiting a pulsar); since then scientists have been trying to understand
    whether some of the stars and planets are similar to our own Solar System.
    It is difficult to examine remote planets directly; the nearby star tends to
    overwhelm any electromagnetic signal, such as light or radio waves. Because
    of that, the team decided to look at how the planetary building blocks
    affect signals from white-dwarf stars. Those are stars which have burnt up
    most of their hydrogen and helium, and shrunk to be very small and dense —
    it is anticipated that our Sun will become a white dwarf in around 5 billion
    years. White dwarfs' atmospheres are composed of either hydrogen or helium,
    which give out a pretty clear and clean spectroscopic signal. However, as
    the star cools, it begins to pull in material from the planets, asteroids,
    comets and so on which had been orbiting it, with some forming a dust disk,
    a little like the rings of Saturn. As that material approaches the star, it
    changes how we see the star. The change is measurable because it influences
    the star's spectroscopic signal, and allows us to identify the type and even
    the quantity of material surrounding the white dwarf. Such measurements can
    be extremely sensitive, allowing bodies as small as an asteroid to be
    detected.
    The team took measurements with spectrographs on the Keck telescope in
    Hawaii, the world's largest optical and infrared telescope, and on the
    Hubble Space Telescope. In that study, the team focused on the sample of
    white dwarfs with dust disks. Astronomers were able to measure the calcium,
    magnesium, and silicon content in most of those stars, and a few additional
    elements in some of them. They may also have found water in one of the
    systems, but have not yet quantified it: it is likely that there will be a
    lot of water in some of those objects. For example, the team previously
    identified one star system, 170 light-years away in the constellation
    Bootes, which was rich in carbon, nitrogen and water, giving a composition
    similar to that of Halley's Comet. In general, though, their composition
    looks very similar to that of the Earth. That would mean that the chemical
    elements, the building blocks of the Earth, are common in other planetary
    systems. From what can be seen, in terms of the presence and proportion of
    those elements, we are normal, pretty normal. And that means that we can
    probably expect to find Earth-like planets elsewhere in our Galaxy. This
    work is still on-going and the recent data release from the Gaia satellite,
    which so far has characterized 1.7 billion stars, has revolutionized the
    field. That means that we will understand the white dwarfs a lot better.
    The team hopes to determine the chemical compositions of extra-solar
    planetary material to a much higher precision.

    STEVE IS NOT AN AURORA
    Spaceweather.com

    A new type of aurora nicknamed 'STEVE' may not be an aurora at all,
    according to a group of researchers who combined satellite data with
    ground-based imagery during a geomagnetic storm to investigate how STEVE is
    formed. The main conclusion is that STEVE is not an aurora. STEVE is a
    purple ribbon of light that amateur astronomers in Canada have been
    photographing for decades, belatedly catching the attention of the
    scientific community in 2016. It doesn't look exactly like an aurora, but
    it often appears alongside aurorae during geomagnetic storms. Is it an
    aurora — or not? That's what the team wanted to find out. Aurorae appear
    when energetic particles from space rain down on the Earth's atmosphere
    during geomagnetic storms. If STEVE is an aurora, they reasoned, it should
    form in much the same way. On 2008 March 28, STEVE appeared over eastern
    Canada just as NOAA's Polar Orbiting Environmental Satellite 17 (POES-17)
    passed overhead. The satellite, which can measure the rain of charged
    particles that causes aurorae, went directly above the purple ribbon. The
    team looked carefully at the old data and found … no rain at all. The
    results verify that that STEVE event is clearly distinct from the aurora
    borealis since it is characterized by the absence of particle precipitation.
    Interestingly, its skyglow could be generated by a new and fundamentally
    different mechanism in the Earth's ionosphere. Another study has shown that
    STEVE appears most often in spring and autumn. With the next equinox only a
    month away, new opportunities to study STEVE are just around the corner.

    A GREEN COMET APPROACHES THE EARTH
    Spaceweather.com

    Comet 21P/Giacobini-Zinner is approaching the Earth. On Sept. 10, it will
    be 0.39 AU (58 million km) from our planet and almost bright enough to see
    with the naked eye. Already it is an easy target for amateur telescopes.
    The comet is relatively small — its nucleus is barely more than a mile in
    diameter — but it is bright and active, and a frequent visitor to the
    inner Solar System as it orbits the Sun once every 6.6 years. On Sept. 10,
    21P/Giacobini-Zinner will not only be near the Earth, but also at peri-
    helion, its closest approach to the Sun. Solar heating will make it
    shine like a star of 6th to 7th magnitude, just below the threshold of
    naked-eye visibility but well within the range of common binoculars.
    21P/Giacobini-Zinner is the parent of the annual Draconid meteor shower, a
    bursty display that typically peaks on Oct. 8. Will the shower be extra
    good this year? Draconid outbursts do tend to occur in years near the
    comet's close approach to the Sun. However, not every close approach brings
    a meteor shower. Forecasters say that there are no known Draconid debris
    streams squarely crossing the Earth's path this year, so we will have to
    wait and see.

    ICE CONFIRMED AT MOON'S POLES
    NASA/Jet Propulsion Laboratory

    A team of scientists has directly observed definitive evidence of water ice
    on the Moon's surface, in the darkest and coldest parts of the Moon's polar
    regions. The ice deposits are patchily distributed and could possibly be
    ancient. At the southern pole, most of the ice is concentrated in craters,
    while the northern pole's ice is more widely, but sparsely, spread. A team
    of scientists used data from NASA's Moon Mineralogy Mapper (M3) instrument
    to identify three specific signatures that definitively prove that there is
    water-ice on the surface of the Moon. M3, aboard the Chandrayaan-1 space-
    craft, launched in 2008 by the Indian Space Research Organization, was
    equipped to confirm the presence of solid ice on the Moon. It collected
    data that not only picked up the reflective properties we would expect from
    ice, but by infrared spectroscopy it could differentiate between liquid
    water or vapour and solid ice. Most of the newfound water ice lies in the
    shadows of craters near the poles, where the temperature never reaches above
    minus 157 Centigrade. Because of the very small tilt of the Moon's rotation
    axis, sunlight never reaches those regions. Previous observations indirect-
    ly found possible signs of surface ice at the lunar south pole, but they
    could have been explained by other phenomena, such as unusually reflective
    lunar soil. With enough ice sitting at the surface — within the top few
    millimetres — water would possibly be accessible as a resource for future
    expeditions to explore and even stay on the Moon, and potentially easier to
    access than the water detected beneath the Moon's surface.

    INSIGHT PASSES HALFWAY POINT TO MARS
    NASA

    NASA's InSight spacecraft, en route to a Nov. 26 landing on Mars, passed the
    halfway mark on Aug. 6. All of its instruments have been tested and are
    working well. The spacecraft has covered 300 million kilometres since its
    launch. It will touch down in Mars' Elysium Planitia region, where it will
    be the first mission to study the planet's deep interior. InSight stands
    for Interior Exploration using Seismic Investigations, Geodesy and Heat
    Transport. The InSight team is using the time before the spacecraft's
    arrival at Mars not only to plan and practise for that critical day,
    but also to activate and check spacecraft sub-systems vital to cruise,
    landing and surface operations, including the highly sensitive scientific
    instruments. InSight's seismometer, which will be used to detect quakes on
    Mars, received a clean bill of health on July 19. The SEIS instrument
    (Seismic Experiment for Interior Structure) is a six-sensor seismometer
    combining two types of sensors to measure ground motions over a wide range
    of frequencies. It will give scientists a window into Mars' internal
    activity.

    STRUCTURALLY 'INSIDE OUT' PLANETARY NEBULA DISCOVERED
    The University of Hong Kong

    Astronomers have discovered the unusual evolution of the central star of a
    planetary nebula in our Milky Way. That discovery sheds light on the future
    evolution, and more importantly, the ultimate fate of the Sun. The research
    team believes that the inverted ionization structure of the nebula is the
    result of the central star undergoing a 'born-again' event, ejecting
    material from its surface and creating a shock that excites the nebular
    material. Planetary nebulae are ionized clouds of gas formed by the
    hydrogen-rich envelopes ejected at late evolutionary stages of low- and
    intermediate-mass stars. As such stars age, they typically strip their
    outer layers, forming a 'wind'. As the star transitions from its red-giant
    phase to become a white dwarf, it becomes hotter, and starts ionizing the
    material in the surrounding wind. That causes the gaseous material closer
    to the star to become highly ionized, while the material further out is less
    so. Studying the planetary nebula HuBi 1 (17,000 light-years away and
    nearly 5 billion years ahead of our Solar System in evolution), however,
    the team found the reverse: HuBi 1's inner regions are less ionized, while
    the outer regions are more so. Analysing the central star, with the
    participation of theoretical astrophysicists, the authors found that it
    is surprisingly cool and metal-rich, and has evolved from a low-mass
    progenitor star which had a mass 1.1 times that of the Sun. The authors
    suggest that the inner nebula was excited by the passage of a shock wave
    caused by the star ejecting matter unusually late in its evolution. The
    stellar material cooled to form circumstellar dust, obscuring the star; that
    would explain why the central star's optical brightness has diminished
    rapidly over the past 50 years. In the absence of ionizing photons from the
    central star, the outer nebula has begun recombining — becoming neutral.
    The authors conclude that, as HuBi 1 was roughly the same mass as the Sun,
    this finding may provide a glimpse of a potential future for our Solar
    System.
    The discovery resolves a long-lasting question regarding the evolutionary
    path of metal-rich central stars of planetary nebulae. The team has been
    using the Nordic Optical Telescope to observe the evolution of HuBi 1 since
    2014, and was among the first astrophysicists to discover its inverted
    ionization structure. After noting that structure and the unusual nature of
    HuBi 1's central star, the observers collaborated with theoretical astro-
    physicists in an effort to find the reasons for what they had observed.
    They came to realize that they had caught HuBi 1 at the exact time when its
    central star underwent a brief 'born-again' process to become a hydrogen-
    poor [WC] and metal-rich star, which is very rare in white-dwarf stars'
    evolution. The findings suggest that the Sun may also experience a 'born-
    again' process while it is dying, about 5000 million years from now; but
    long before that event the Earth will be engulfed by the Sun when it expands
    into a red giant and nothing living will survive.

    WATER WORLDS ARE COMMON
    Goldschmidt Conference

    Scientists have shown that water is likely to be a major component of those
    exoplanets (planets orbiting other stars) which are between two and four
    times the size of the Earth. That has implications for the search for life
    in our Galaxy. The 1992 discovery of exoplanets orbiting other stars has
    sparked interest in understanding the compositions of those planets, to
    determine, among other goals, whether they are suitable for the development
    of life. Now a new evaluation of data from the exoplanet-hunting Kepler
    Space Telescope and the Gaia mission indicates that many of the known
    planets may contain as much as 50% water. That is very much more than the
    Earth's 0.02% (by weight) water content. Scientists have found that many of
    the 4000 confirmed or candidate exoplanets discovered so far fall into two
    size categories: those with the planetary radii averaging around 1.5 times
    that of the Earth, and those averaging around 2.5 Earth radii. Now a group
    of scientists, after analyzing the exoplanets with mass measurements and
    recent radius measurements from the Gaia satellite, has developed a model
    of their internal structure. The group has looked at how mass relates to
    radius, and developed a model which might explain the relationship. The
    model indicates that those exoplanets which have radii of around 1.5 Earth
    radii tend to be rocky planets (of typically five times the mass of the
    Earth), while those with radii of about 2.5 Earth radii (with masses around
    ten times that of the Earth) are probably water worlds.
    Their water is not as is commonly found here on Earth. Their surface
    temperatures are expected to be in the 200- to 500-degree Celsius range.
    Their surfaces may be shrouded in a water-vapour-dominated atmosphere, with
    a liquid water layer underneath. Deeper down, one would expect to find the
    that the water transforms into high-pressure ices before one reaches the
    solid rocky core. The beauty of the model is that it explains just how
    composition relates to the known facts about such planets. The data
    indicate that about 35% of all known exoplanets which are bigger than the
    Earth should be water-rich. Those water worlds probably formed in ways
    similar to the giant-planet cores (Jupiter, Saturn, Uranus, Neptune) which
    we find in our own Solar System. The newly-launched TESS mission is
    expected to find many more of them, with the help of ground-based spectro-
    scopic follow-up.

    GALAXY CLUSTER HIDING IN PLAIN SIGHT
    Massachusetts Institute of Technology

    MIT scientists have uncovered a sprawling new galaxy cluster hiding in plain
    sight. The cluster, which is 2.4 billion light-years away, is made up of
    hundreds of individual galaxies and surrounds an extremely active super-
    massive black hole, or quasar. The central quasar is called PKS1353-341 and
    is intensely bright — so bright that for decades astronomers observing it
    in the night sky have assumed that the quasar was quite alone in its corner
    of the Universe, shining out as a solitary light source from the centre of a
    single galaxy. The researchers estimate that the cluster has a mass of
    about 690 times 10 to the 12 Suns. Our Milky Way galaxy, for comparison,
    weighs in at around 400,000 million solar masses. The team also calculates
    that the quasar at the centre of the cluster is 46 billion times brighter
    than the Sun. Its extreme luminosity is probably the result of a temporary
    feeding frenzy: as an immense disk of material swirls around the quasar, big
    chunks of matter from the disk are falling in and feeding it, causing the
    black hole to radiate huge amounts of energy out as light. That might be a
    short-lived phase that clusters go through, where the central black hole has
    a quick meal, gets bright, and then fades away again. Some astronomers
    believe that the discovery of the hidden cluster inplies there may be other
    similar galaxy clusters hiding behind extremely bright objects that
    astronomers have mis-catalogued as single light sources. The researchers
    are now looking for more hidden galaxy clusters, which could be important
    clues to estimating how much matter there is in the Universe and how fast
    the Universe is expanding.
    In 2012, the team discovered the Phoenix cluster, one of the most massive
    and luminous galaxy clusters in the Universe. The mystery was why that
    cluster, which was so intensely bright and in a region of the sky that is
    easily observable, had not been found before. It is because astronomers had
    preconceived notions of what a cluster should look like. For the most part,
    astronomers have assumed that galaxy clusters look 'fluffy', giving a very
    diffuse signal in the X-ray band, unlike brighter, point-like sources, which
    have been interpreted as extremely active quasars or black holes. The
    images are either all points, or fluffs; the points are black holes that are
    accreting gas and glowing as the gas spirals in, and the fluffs are great
    million-light-year balls of hot gas that we call clusters. The Phoenix
    discovery proved that galaxy clusters could indeed host immensely active
    black holes, prompting astronomers to wonder whether there could be other
    'nearby' galaxy clusters that were simply misidentified. To answer that
    question, the researchers set up a survey named CHiPS, for Clusters Hiding
    in Plain Sight, which was designed to re-evaluate X-ray images taken in the
    past. For every point source that was previously identified, the
    researchers noted the coordinates and then studied them more directly with
    the Magellan Telescope, a powerful optical telescope in Chile. If they
    observed a higher-than-expected number of galaxies surrounding the point
    source (a sign that the gas may stem from a cluster of galaxies), the
    researchers looked at the source again, using NASA's space-based Chandra
    X-Ray Observatory, to identify an extended, diffuse source around the main
    point source. Some 90% of the sources turned out to not be clusters. The
    team plans to comb through more X-ray data in search of galaxy clusters that
    might have been missed the first time.

    SOME OF THE OLDEST GALAXIES IN UNIVERSE
    Durham University

    Astronomers from the Institute for Computational Cosmology at Durham
    University and the Harvard-Smithsonian Center for Astrophysics have found
    evidence that the faintest satellite galaxies orbiting our own Milky Way
    galaxy are amongst the very first galaxies that formed in the Universe.
    Scientists working on that research have described the finding as “hugely
    exciting”. The research group's findings suggest that galaxies including
    Segue-1, Bootes I, Tucana II and Ursa Major I are in fact some of the first
    galaxies ever formed, thought to be over 13 billion years old. When the
    Universe was about 380,000 years old, the very first atoms formed. They
    were atoms of hydrogen, the simplest element in the Periodic Table. Those
    atoms collected into clouds and began to cool gradually and settle into the
    small clumps or 'haloes' of dark matter that emerged from the Big Bang.
    That cooling phase, known as the 'Cosmic dark ages', lasted about 100
    million years. Eventually, the gas that had cooled inside the haloes
    became unstable and began to form stars — these objects are the very first
    galaxies ever to have formed. With the formation of the first galaxies, the
    Universe burst into light, bringing the cosmic dark ages to an end.
    The team identified two populations of satellite galaxies orbiting the Milky
    Way. The first was a very faint population consisting of the galaxies that
    formed during the 'cosmic dark ages'. The second was a slightly brighter
    population consisting of galaxies that formed hundreds of millions of years
    later, once the hydrogen that had been ionized by the intense ultraviolet
    radiation emitted by the first stars was able to cool into more massive dark
    matter haloes. Remarkably, the team found that a model of galaxy formation
    that it had developed previously agreed perfectly with the data, allowing it
    to infer the formation times of the satellite galaxies. The finding
    supports the current model for the evolution of the Universe, the 'Lambda-
    cold-dark-matter model' in which the elementary particles that make up the
    dark matter drive cosmic evolution. The intense ultraviolet radiation
    emitted by the first galaxies destroyed the remaining hydrogen atoms by
    ionizing them (knocking out their electrons), making it difficult for that
    gas to cool and form new stars. The process of galaxy formation ground to a
    halt and no new galaxies were able to form for the next billion years or so.
    Eventually, the haloes of dark matter became so massive that even ionized
    gas was able to cool. Galaxy formation resumed, culminating in the formation
    of spectacular bright galaxies like our own Milky Way. A decade ago, the
    faintest galaxies in the vicinity of the Milky Way would have gone under the
    radar. With the increasing sensitivity of present and future galaxy counts,
    a whole new trove of the tiniest galaxies has come to light, allowing us to
    test theoretical models in new regimes.

    EARLY OPAQUE UNIVERSE LINKED TO GALAXY SCARCITY
    University of California – Riverside

    A team of astronomers has made a surprising discovery: 12.5 billion years
    ago, the most opaque place in the Universe contained relatively little
    matter. It has long been known that the Universe is filled with a web-like
    network of dark matter and gas. That 'cosmic web' accounts for most of the
    matter in the Universe, whereas galaxies like our own Milky Way make up only
    a small fraction. Today, the gas between galaxies is almost totally
    transparent because it is kept ionized — electrons detached from their
    atoms — by a bath of energetic ultraviolet radiation. Over a decade ago,
    astronomers noticed that in the very distant past — roughly 12.5 billion
    years ago, or about 1 billion years after the Big Bang — the gas in deep
    space was not only highly opaque to ultraviolet light, but its transparency
    varied widely from place to place, obscuring much of the light emitted by
    distant galaxies. Then a few years ago, a team at the University of
    Cambridge found that those differences in opacity were so large that either
    the amount of gas itself, or more likely the radiation in which it is
    immersed, must vary substantially from place to place. Today, we live in a
    fairly homogeneous Universe. If you look in any direction you find, on
    average, roughly the same number of galaxies and similar properties for the
    gas between galaxies, the so-called intergalactic gas. At that early time,
    however, the gas in deep space looked very different from one region of the
    Universe to another. To find out what created the differences, astronomers
    used one of the largest telescopes in the world, the Subaru telescope on the
    summit of Mauna Kea in Hawaii. Using its powerful camera, the team looked
    for galaxies in a vast region, roughly 300 million light-years in size,
    where they knew the intergalactic gas was extremely opaque.
    For the cosmic web, more opacity normally means more gas, and hence more
    galaxies. But the team found the opposite: the region contained far fewer
    galaxies than average. Because the gas in deep space is kept transparent by
    the ultraviolet light from galaxies, fewer galaxies nearby might make it
    murkier. Normally it does not matter how many galaxies are nearby; the
    ultraviolet light that keeps the gas in deep space transparent often comes
    from galaxies that are extremely far away. At that very early time, it
    looks as if the UV light could not travel very far, so a patch of the
    Universe with few galaxies in it would look much darker than one with plenty
    of galaxies around. That discovery may eventually shed light on another
    phase in cosmic history. In the first billion years after the Big Bang,
    ultraviolet light from the first galaxies filled the Universe and
    permanently transformed the gas in deep space. Astronomers believe that
    that occurred earlier in regions with more galaxies, so the large fluctua-
    tions in intergalactic radiation may be a relic of that patchy process, and
    could offer clues to how and when it occurred. By studying both galaxies
    and the gas in deep space, astronomers hope to get closer to understanding
    how the intergalactic ecosystem took shape in the early Universe.

    ANCIENT QUASARS CONFIRM QUANTUM ENTANGLEMENT
    Massachusetts Institute of Technology

    Last year, physicists at MIT, the University of Vienna, and elsewhere
    provided strong support for quantum entanglement, the seemingly far-out idea
    that two particles, no matter how distant from each other in space and time,
    can be inextricably linked, in a way that defies the rules of classical
    physics. Take, for instance, two particles sitting on opposite edges of the
    Universe. If they are truly entangled, then according to the theory of
    quantum mechanics their physical properties should be related in such a way
    that any measurement made on one particle should instantly convey
    information about any future measurement outcome of the other particle —
    correlations that Einstein sceptically saw as “spooky action at a distance”.
    In the 1960s, the physicist John Bell calculated a theoretical limit beyond
    which such correlations must have a quantum, rather than a classical,
    explanation. But what if such correlations were the result not of quantum
    entanglement, but of some other hidden, classical explanation? Such
    “what-ifs” are known to physicists as loopholes to tests of Bell's
    inequality, the most stubborn of which is the 'freedom-of-choice' loophole:
    the possibility that some hidden, classical variable may influence the
    measurement that an experimenter chooses to perform on an entangled
    particle, making the outcome look quantumly correlated when in fact it
    isn't. Last February, the MIT team and their colleagues significantly
    constrained the freedom-of-choice loophole, by using 600-year-old starlight
    to decide what properties of two entangled photons to measure. Their
    experiment proved that, if a classical mechanism caused the correlations
    they observed, it would have to have been set in motion more than 600 years
    ago, before the stars' light was first emitted and long before the actual
    experiment was even conceived. Now, the same team has vastly extended the
    case for quantum entanglement and further restricted the options for the
    freedom-of-choice loophole. The researchers used distant quasars, one of
    which emitted its light 7.8 billion years ago and the other 12.2 billion
    years ago, to determine the measurements to be made on pairs of entangled
    photons. They found correlations among more than 30,000 pairs of photons,
    to a degree that far exceeded the limit that Bell originally calculated for
    a classically based mechanism. If some conspiracy is happening to simulate
    quantum mechanics by a mechanism that is actually classical, that mechanism
    would have had to begin its operations — somehow knowing exactly when,
    where, and how this experiment was going to be done — at least 7.8 billion
    years ago. That seems incredibly implausible, so we have very strong
    evidence that quantum mechanics is the right explanation. The Earth is
    about 4.5 billion years old, so any alternative mechanism — different from
    quantum mechanics — that might have produced our results by exploiting such
    a loophole would have had to be in place long before even there was a planet
    Earth, let alone an MIT. So we have pushed any alternative explanations
    back to very early in cosmic history.

    15 YEARS IN SPACE FOR SPITZER SPACE TELESCOPE
    NASA

    Initially scheduled for a minimum 2.5-year primary mission, NASA's Spitzer
    Space Telescope has gone far beyond its expected lifetime — and is still
    going strong after 15 years. Launched into a solar orbit on 2003 Aug. 25,
    Spitzer was the last of NASA's four Great Observatories to reach space. The
    space telescope has illuminated some of the oldest galaxies in the Universe,
    revealed a new ring around Saturn, and peered through shrouds of dust to
    study newborn stars and black holes. Spitzer assisted in the discovery of
    planets beyond our Solar System, including the detection of seven Earth-size
    planets orbiting the star TRAPPIST-1, among other accomplishments. Spitzer
    detects infrared light — most often heat radiation emitted by warm objects.
    Each of the four Great Observatories collects light in a different range of
    wavelength. By combining their observations of various objects and regions,
    scientists can gain a more complete picture of the Universe. Spitzer has
    logged over 106,000 hours of observation time. Thousands of scientists
    around the world have utilized Spitzer data in their studies, and Spitzer
    data are cited in more than 8,000 published papers.
    Spitzer's primary mission ended up lasting 5.5 years, during which time the
    spacecraft operated in a 'cold phase', with a supply of liquid helium
    cooling three onboard instruments to just above absolute zero. The cooling
    system reduced excess heat from the instruments themselves that could
    contaminate their observations. That gave Spitzer very high sensitivity for
    'cold' objects. In 2009 July, after Spitzer's helium supply ran out, the
    spacecraft entered a so-called 'warm phase'. Spitzer's main instrument,
    called the Infrared Array Camera (IRAC), has four cameras, two of which
    continue to operate in the warm phase with the same sensitivity that they
    maintained during the cold phase. Spitzer orbits the Sun in an Earth-
    trailing orbit (meaning it literally follows behind the Earth as the planet
    orbits the Sun) and has continued to fall further and further behind the
    Earth during its lifetime. This now poses a challenge for the spacecraft,
    because while it is downloading data to Earth, its solar panels do not
    directly face the Sun. As a result, Spitzer must use battery power during
    data downloads. The batteries are then recharged between downloads. In
    2016, Spitzer entered an extended mission dubbed 'Spitzer Beyond'. The
    spacecraft is currently scheduled to continue operations till 2019 November,
    more than 10 years after entering its warm phase.

    Bulletin compiled by Clive Down
    http://www.popastro.com

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