The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 442 2017 March 19

Welcome to Pembrokeshire U3A Forums Astronomy Group The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 442 2017 March 19

  • This topic is empty.
Viewing 1 post (of 1 total)
  • Author
    Posts
  • #9166
    Anonymous

    The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 442 2017 March 19

    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/

    CANADIAN FOSSILS ARE OLDEST EVIDENCE OF LIFE
    Live Science

    Fossil microbes almost 4.3 Canadian-billion years old that have been
    found in Canada are similar to the bacteria that thrive today around
    sea-floor hydrothermal vents and may represent the oldest known
    evidence of life on Earth. Researchers said that the fossils, from
    the Hudson Bay shoreline in northern Quebec near the Nastapoka
    Islands, lend credence to the hypothesis that hydrothermal vents
    spewing hot water may have been the cradle of life on Earth relatively
    soon after the planet formed. They also said that they thought that
    at that time Mars had oceans, long since gone, that may have boasted
    similar conditions conducive to the advent of life. Tiny filaments
    and tubes made of iron oxide, formed by the microbes, were found
    encased in layers of quartz that experts have determined to be between
    3.7 and 4.28 billion years old, according to the study published in the
    'Nature'. The researchers expressed confidence that the fossils were
    formed by organisms, saying no non-biological explanation was plausible.
    It was primordial microbes like those described in the study that set
    in motion the evolutionary march toward complex life and, eventually,
    the appearance of humans 200,000 years ago. The scientists said that
    the primordial microbes' structure closely resembled modern bacteria
    that dwell near iron-rich hydrothermal vents. They believe that, like
    their modern counterparts, they were iron-eaters. The rock's compo-
    sition was consistent with a deep-sea vent environment. The Earth
    formed about 4.5 billion years ago and the oceans appeared about 100
    million years later. If the fossils are indeed 4.28 billion years old, that would
    suggest an almost instantaneous emergence of life after ocean formation.
    The fossils appear to be older than any other previously discovered
    evidence of life. For example, other scientists last year described 3.7
    billion-year-old fossilized microbial mats, called stromatolites, from
    Greenland.

    WATER-RICH HISTORY OF MARS — NEW EVIDENCE
    DOE/Lawrence Berkeley National Laboratory

    Mars may have been a wetter place than previously thought, according
    to research on simulated Martian meteorites. Researchers found
    evidence that a mineral found in Martian meteorites — which had been
    considered as proof of an ancient dry environment on Mars — may have
    originally been a hydrogen-containing mineral that could indicate a
    more water-rich history for the Red Planet. An international research
    team in the study, created a synthetic version of a hydrogen-
    containing mineral known as whitlockite. After shock-compression
    experiments on whitlockite samples that simulated the conditions of
    ejecting meteorites from Mars, the researchers studied their
    microscopic make-up with X-ray experiments at Berkeley Lab's Advanced
    Light Source (ALS) and at Argonne National Laboratory's Advanced
    Photon Source (APS). The X-ray experiments showed that whitlockite
    can become dehydrated by such shocks, forming merrillite, a mineral
    that is commonly found in Martian meteorites but does not occur
    naturally on the Earth. This is important for deducing how much water
    could have been on Mars, and whether the water was from Mars itself
    rather than comets or meteorites. If even *some* of the merrillite
    had been whitlockite before, it changes the water budget of Mars
    dramatically. And because whitlockite can be dissolved in water and
    contains phosphorus, an essential element for life on Earth — and
    merrillite appears to be common to many Martian meteorites — the
    study could also have implications for the possibility of life on
    Mars. The overarching question here is about water on Mars and its
    early history on Mars: had there ever been an environment that enabled
    a generation of life on Mars? The pressures and temperatures
    generated in the shock experiments, while comparable to those of a
    meteorite impact, lasted for only about a ten-millionth of a second,
    or about one-tenth to one-hundredth as long as an actual meteorite
    impact. The fact that experiments showed even partial conversion to
    merrillite in lab- created conditions suggested that a longer-duration
    impact might have produced 'almost full conversion' to merrillite.
    There is also evidence that liquid water flows on Mars today, though
    there has not been any scientific proof that life has ever existed on
    Mars. In 2013, planetary scientists reported that darkish streaks
    that appear on Martian slopes are probably related to periodic flows
    of water that result from changing temperatures. They based their
    analysis on data from the Mars Reconnaissance Orbiter. And last
    November, NASA scientists reported that a large underground body of
    water ice in one region of Mars contains the equivalent of all of the
    water in Lake Superior, the largest of the Great Lakes in America.
    Analyses of surface rocks during Mars rover explorations have also
    found evidence of a former abundance of water. The only missing link
    now is a proof that merrillite had, in fact, really been Martian
    whitlockite before. The team is pursuing another round of studies
    using infrared light at the ALS to study actual Martian meteorite
    samples, and are also planning X-ray studies of those samples this
    year. Many Martian meteorites found on the Earth seem to come from a
    period of about 150 to 586 million years ago, and most are probably
    from the same region of Mars. These meteorites are probably excavated
    from a depth of about a kilometre below the surface by the initial
    impact that sent them out into space, so they are not representative
    of the more recent 'geology' at the surface of Mars. Most of them are
    very similar in composition as well as in the minerals that are
    occurring, and have a similar impact age. Mars is likely to have
    formed about 4.6 billion years ago, about the same time as
    the Earth and the rest of the Solar System. Researchers noted that,
    despite detailed studies of Martian meteorites coupled with thermal
    imaging of Mars taken from orbiters, and rock samples analyzed by
    rovers traversing the planet's surface, the best evidence of Mars'
    water history would come actual Martian rocks taken from the planet
    and transported back here, intact, for detailed studies.

    DAWN IDENTIFES AGE OF CERES' BRIGHTEST AREA
    NASA

    The bright central area of Ceres' Occator Crater, known as Cerealia
    Facula, is approximately 30 million years younger than the crater in
    which it lies. Scientists used data from the Dawn spacecraft to
    analyze Occator's central dome in detail, concluding that that
    intriguing bright feature is only about 4 million years old.
    Researchers analyzed data from two instruments on board the spacecraft
    — the framing camera, and the visible and infrared mapping
    spectrometer. The new study supports earlier interpretations from the
    Dawn team that the reflective material — the brightest area on Ceres
    — is made of carbonate salts, although it did not confirm a
    particular type of carbonate previously identified. The secondary,
    smaller bright areas of Occator, called Vinalia Faculae, are comprised
    of a mixture of carbonates and dark material. New evidence also
    suggests that Occator's bright dome probably rose in a process that
    took place over a long period of time, rather than forming in a single
    event. The authors of the study believe that the initial trigger was
    the impact that dug out the crater itself, causing briny liquid to
    rise closer to the surface. Water and dissolved gases, such as carbon
    dioxide and methane, came up and created a vent system. The rising
    gases could also have forced carbonate-rich materials to ascend toward
    the surface. During that period, the bright material would have
    erupted through fractures, eventually forming the dome that we see
    today.

    STAR CLUSTER DISCOVERY UPSETS THEORIES
    RAS

    The discovery of young stars in old star clusters could send
    scientists back to the drawing board for one of the Universe's most
    common objects. There is an enormous number of stars in the Universe
    and we have been observing and classifying those we can see for more
    than a century. Our models of stellar evolution are based on the
    assumption that stars within star clusters formed from the same
    material at roughly the same time. A star cluster is a group of stars
    that share a common origin and are held together by gravity for some
    length of time. Because star clusters are assumed to contain stars of
    similar age and composition, researchers have used them as 'astronom-
    ical laboratories' to understand how mass affects the evolution of
    stars. If the assumption turns out to be incorrect, as some findings
    suggest, then the important models will need to be revisited and
    revised.
    The discovery involves a study of star clusters in the Large Magell-
    anic Cloud. By cross-matching the locations of several thousand young
    stars with the locations of stellar clusters, the researchers found 15
    stellar candidates that were much younger than other stars within the
    same cluster. The formation of those younger stars might have been
    fuelled by gas entering the clusters from interstellar space, but that
    possibility was eliminated by observations made by radio telescopes
    that showed no correlation between interstellar hydrogen gas and the
    locations of the clusters being studied. Scientists believe that the
    younger stars have actually been created out of the matter ejected
    from older stars as they die, which would mean that we are seeing
    multiple generations of stars belonging to the same cluster. The
    stars concerned are too faint to see with optical telescopes because
    of the dust that surrounds them. They have been observed at infrared
    wavelengths by the orbiting space telescopes Spitzer and Herschel.
    An envelope of gas and dust surrounds the young stars, but as they
    become more massive and that shroud blows away, they will become
    visible at optical wavelengths to powerful instruments like the
    Hubble Space Telescope. If scientists point Hubble at the clusters
    being studied, astronomers should be able to see both young and old
    stars and confirm once and for all that star clusters can contain
    several generations of stars.

    STAR ORBITS BLACK HOLE EVERY 28 MINUTES
    Michigan State University

    Astronomers have found evidence for a star that orbits a black hole
    about twice an hour — the tightest orbit ever witnessed for a black
    hole and a companion star. The discovery team used the Chandra X-ray
    Observatory as well as NuSTAR and the Australia Telescope Compact
    Array. The close-in stellar binary is located in the globular cluster
    47 Tucanae, a dense cluster of stars in our Galaxy about 15,000 light-
    years away. While astronomers have observed that binary for many
    years, it was not until 2015 that radio observations revealed that the
    pair probably contains a black hole pulling material from a white-
    dwarf companion, a low-mass star that has exhausted its nuclear fuel.
    New Chandra data of the system, which is known as X9, show that it
    changes in X-ray brightness in the same manner every 28 minutes, which
    is probably the length of time that it takes the companion star to
    make one complete orbit around the black hole. Chandra data also show
    evidence for large amounts of oxygen in the system — a characteristic
    of white dwarfs. A strong case can, therefore, be made that that the
    companion star is a white dwarf, which would then be orbiting the
    black hole at only about 2.5 times the separation between the Earth
    and the Moon. The white dwarf is so close to the hole that material
    is being pulled away from the star and dumped onto a disc of matter
    around the black hole before falling in. Although the white dwarf
    does not appear to be in immediate danger of falling in or being torn
    apart by the black hole, its fate is uncertain.
    For a long time astronomers thought that black holes were rare or
    absent in globular star clusters. The recent discovery is evidence
    that, rather than being one of the worst places to look for black
    holes, globular clusters might be one of the best. How did the black
    hole get such a close companion? One possibility is that the black
    hole smashed into a red-giant star, and then gas from the outer
    regions of the star was ejected from the binary. The remaining core
    of the red giant would form into a white dwarf, which became a binary
    companion to the black hole. The orbit of the binary would then have
    shrunk as gravitational waves were emitted, until the black hole
    started pulling material from the white dwarf. The gravitational
    waves currently being produced by the binary have a frequency that is
    too low to be detected with the Laser Interferometer Gravitational-
    Wave Observatory, LIGO, that has recently detected gravitational waves
    from merging black holes. Sources like X9 could potentially be
    detected with future gravitational-wave observatories in space. An
    alternative explanation for the observations is that the white dwarf
    is partnered by a neutron star, rather than a black hole. In that
    scenario, the neutron star spins faster as it pulls material from a
    companion star via a disc, a process that can decrease the rotational
    period of the neutron star to a few thousandths of a second. A few
    such objects, called transitional millisecond pulsars, have been
    observed near the end of such a spinning-up phase. The team does not
    favour that possibility, as transitional millisecond pulsars have
    properties not seen in X9, such as extreme variability at X-ray and
    radio wavelengths.

    STARDUST SHEDS LIGHT ON FIRST STARS
    ESO

    A team of astronomers has used the Atacama Large Millimetre/submilli-
    metre Array (ALMA) to observe A2744_YD4, the youngest and most remote
    galaxy ever seen by ALMA. It was surprised to find that that youthful
    galaxy contained an abundance of interstellar dust — dust formed by
    the deaths of an earlier generation of stars. Follow-up observations
    using the X-shooter instrument on the Very Large Telescope confirmed
    the enormous distance to A2744_YD4. The galaxy appears to us as it
    was when the Universe was only 600 million years old, during the
    period when the first stars and galaxies were forming. Cosmic dust is
    mainly composed of silicon, carbon and aluminium, in grains as small
    as a millionth of a centimetre across. The chemical elements in the
    grains are forged inside stars and are scattered across the cosmos
    when the stars die, most spectacularly in supernova explosions, the
    final fate of short-lived, massive stars. Today, such dust is
    plentiful and is a key building block in the formation of stars,
    planets and complex molecules; but in the early Universe, before the
    first generations of stars died out, it was scarce. The observations
    of the dusty galaxy A2744_YD4 were made possible because it lies
    behind a massive galaxy cluster called Abell 2744. Gravitational
    lensing causes the cluster to magnify the more distant A2744_YD4 by
    about 1.8 times, allowing the team to peer far back into the early
    Universe. The ALMA observations also detected the glowing emission of
    ionized oxygen from A2744_YD4. This is the most distant, and hence
    earliest, detection of oxygen in the Universe, surpassing another ALMA
    result from 2016.
    The detection of dust in the early Universe provides new information
    on when the first supernovae exploded and hence the time when the
    first hot stars bathed the Universe in light. Determining the timing
    of that 'cosmic dawn' is one of the 'holy grails' of modern astronomy,
    and it can be indirectly probed through the study of early inter-
    stellar dust. The team estimates that A2744_YD4 contained an amount
    of dust equivalent to 6 million times the mass of the Sun, while the
    galaxy's total stellar mass was 2000 million solar masses. The team
    also measured the rate of star formation in A2744_YD4 and found that
    stars are forming at a rate of 20 solar masses per year, compared to
    just one solar mass per year in the Milky Way. That means that
    significant star formation began approximately 200 million years
    before the epoch at which the galaxy is being observed. That provides
    a great opportunity for ALMA to help study the era when the first
    stars and galaxies 'switched on' — the earliest epoch yet probed.

    LOST LUNAR SPACECRAFT FOUND
    NASA

    Finding derelict spacecraft and space debris in orbit round the Earth
    is a technological challenge. Detecting such objects in orbit round
    the Moon is even more difficult. Optical telescopes are unable to
    search for small objects hidden in the bright glare of the Moon.
    However, a new technological application of interplanetary radar has
    successfully located spacecraft orbiting the Moon — one active, and
    one dormant. The new technique could assist planners of future moon
    missions. Scientists have been able to detect NASA's Lunar
    Reconnaissance Orbiter [LRO] and the Indian Space Research Organiz-
    ation's Chandrayaan-1 spacecraft in lunar orbit with ground-based
    radar. Finding LRO was relatively easy, as they were working with the
    mission's navigators and had precise orbit data where it was located.
    Finding India's Chandrayaan-1 required a bit more detective work
    because the last contact with the spacecraft was in 2009 August.
    Also, the Chandrayaan-1 spacecraft is very small, a cube about 1.5
    metres on a side. Although the interplanetary radar has been used to
    observe small asteroids several million miles away, researchers were
    not certain that an object of such small size as Chandrayaan-1 as far
    away as the Moon could be detected, even with the most powerful
    radars. Chandrayaan-1 proved the perfect target for demonstrating the
    capability of the technique.
    While they all use microwaves, not all radar transmitters are equal.
    The average police radar gun has an operational range of about 2 km,
    while air-traffic-control radar goes to about 100 km. To find a
    spacecraft 380,000 kilometres away, JPL's team used a 70-metre antenna
    to send out a powerful beam of microwaves directed toward the Moon.
    Then the radar echoes that bounced back from lunar orbit were received
    by the 100-metre Green Bank Telescope. The team used data from the
    return signal to estimate its velocity and the distance to the target
    and its velocity. That information was then used to update the orbital
    predictions for Chandrayaan-1. Radar echoes from the spacecraft were
    obtained seven more times over three months and are in perfect
    agreement with the new orbital predictions.

    NASA MISSION NAMED 'EUROPA CLIPPER'
    NASA

    NASA's upcoming mission to investigate the habitability of Jupiter's
    icy moon Europa now has a formal name: Europa Clipper. The moniker
    harks back to the clipper ships that sailed across the Earth's oceans
    in the 19th century. Clipper ships were streamlined, three-masted
    sailing vessels renowned for their grace and swiftness. They rapidly
    shuttled tea and other goods back and forth across the Atlantic Ocean
    and around the globe. In the grand tradition of those classic ships,
    the Europa Clipper spacecraft would sail past Europa at a rapid
    cadence, as frequently as every two weeks, providing many opportuni-
    ties to investigate the moon up close. The mission plan includes 40
    to 45 fly-bys, during which the spacecraft would image the moon's icy
    surface at high resolution and investigate its composition and the
    structure of its interior and icy shell. Europa has long been a high
    priority for exploration because it holds a salty liquid water ocean
    beneath its icy crust. The ultimate aim of Europa Clipper is to
    determine if Europa is habitable, possessing all three of the
    ingredients necessary for life: liquid water, chemical ingredients,
    and energy sources sufficient to enable biology. During each orbit,
    the spacecraft will spend only a short time within the challenging
    radiation environment near Europa. The mission is being planned for
    launch in the 2020s, arriving in the Jupiter system after a journey of
    several years.

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

    The Society for Popular Astronomy has been helping beginners in
    amateur astronomy — and more experienced observers — for more than
    60 years. If you are not a member, you may be missing something.
    Membership rates are extremely reasonable, starting at just £20 a
    year in the UK. You will receive our bright bi-monthly magazine
    Popular Astronomy, help and advice in pursuing your hobby, the chance
    to hear top astronomers at our regular meetings, and other benefits.
    The best news is that you can join online right now with a credit or
    debit card at our lively web site: http://www.popastro.com

Viewing 1 post (of 1 total)
  • You must be logged in to reply to this topic.