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November 8, 2015 at 4:23 pm #8678Anonymous
The SOCIETY for POPULAR ASTRONOMY
Electronic News Bulletin No. 409 2015 November 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 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/
COMET LOVEJOY RELEASES MANY DIFFERENT MOLECULES INTO SPACE
NASA/Goddard Space Flight Center
Astronomers at the Paris Observatory observing Comet Lovejoy have found 21 different 'organic' (carbon-containing) molecules in gas from the comet, including ethyl alcohol and glycolaldehyde, a simple sugar. Comets are frozen remnants from the formation of our Solar System. Scientists are interested in them because they are relatively pristine and therefore hold clues to how the Solar System was made. Most of them orbit in frigid zones far from the Sun. However, occasionally, a gravitational disturbance sends a comet into an orbit that brings it closer to the Sun, where it heats up and releases gases, allowing scientists to determine its composition. Comet Lovejoy (formally catalogued as C/2014 Q2) was one of the brightest and most active comets since Hale-Bopp in 1997.
Comet Lovejoy passed closest to the Sun on 2015 January 30. Astronomers from the Paris Observatory observed it around that time, when it was brightest and most active. They observed at microwave wavelengths with the 30-metre radio telescope at Pico Veleta in the Sierra Nevada mountains in southern Spain. Sunlight energizes molecules in the comet's atmosphere, causing them to glow at specific microwave frequencies (if microwaves were visible, different frequencies would be perceived as different colours). Each kind of molecule glows at specific, signature frequencies, exactly analogous to spectral lines in optical spectra. The equipment was able to analyze a wide range of frequencies simultaneously, allowing the team to determine the types and amounts of many different molecules in the comet despite the shortness of the observation period. The comet was found to be releasing water at the rate of 20 tons per second. 21 different 'organic' molecules (i.e. molecules containing carbon) were identified in gas from the comet, including ethyl alcohol and glycolaldehyde, a simple sugar. The rate of ethyl alcohol release was about 50 kilograms a second — as much as there is in about 500 bottles of wine.
Some researchers think that comet impacts on the ancient Earth delivered a supply of organic molecules that could have assisted the origin of life. Discovery of complex organic molecules in Lovejoy and other comets offers some support for that hypothesis. It obviously shows, at least, that some comets carry complex chemistry. During the 'Late Heavy Bombardment' about 3.8 billion years ago, when many comets and asteroids were impacting onto the Earth, which was getting its first oceans, life did not need to start with just simple molecules like water, carbon monoxide, and nitrogen; there would already have been molecules with multiple carbon atoms. So we can see where sugars start forming, as well as more complex organics such as amino acids — the building blocks of proteins — or nucleobases, the building blocks of DNA. Those can start forming much more easily from already rather complex molecules rather than beginning with molecules with only two or three atoms. In July, the European Space Agency reported that the Philae lander from its Rosetta spacecraft in orbit around comet 67P/Churyumov-Gerasimenko detected 16 organic compounds as it dropped toward and then bounced across the comet's surface. According to the agency, some of the compounds detected play key roles in the creation of amino acids, nucleobases, and sugars from simpler 'building-block' molecules.
Astronomers think that comets preserve material from the ancient cloud of gas and dust that formed the Solar System. Exploding stars (supernovae) and the winds from red-giant stars near the end of their lives produce vast clouds of gas and dust. Solar systems are born when shock waves from stellar winds and other nearby supernovae compress and concentrate a cloud of ejected stellar material until dense clumps of that cloud begin to collapse under their own gravity, forming a new generation of stars and planets. Such clouds contain countless dust grains. Carbon dioxide, water, and other gases form a layer of frost on the surfaces of the grains, just as frost forms on grass during cold, clear nights. Radiation in space powers chemical reactions in the frost layer to produce complex organic molecules. The icy grains become incorporated into comets and asteroids, some of which impact upon young planets like the ancient Earth, delivering the organic molecules contained within them. The next step is to see whether the organic material being found in comets may have come from the primordial cloud that formed the Solar System, or whether it was created later on, inside the proto-planetary disc that surrounded the young Sun.
JUPITER EJECTED GIANT PLANET FROM SOLAR SYSTEM
University of Toronto
Astrophysicists at the University of Toronto have found that a close encounter with Jupiter about four billion years ago may have resulted in another planet's ejection from the Solar System altogether. The idea of the existence of a fifth gas-giant planet at the time of the Solar System's formation — in addition to Jupiter, Saturn, Uranus and Neptune — was first proposed in 2011. But if it did exist, how did it get pushed out? Scientists have suspected thatthe ouster was either Saturn or Jupiter. Planet ejections occur as a result of a close planetary encounter in which one of the objects is accelerated so much that it breaks free from the massive gravitational pull of the Sun. However, earlier studies which proposed that giant planets could possibly eject one another did not consider the effects that such violent encounters would have on minor bodies, such as the known moons of the giant planets, and their orbits. So astronomers turned their attention to moons and orbits, developing computer simulations based on the modern-day trajectories of Callisto and Iapetus, regular moons orbiting Jupiter and Saturn respectively. They then measured the likelihood of each one producing its current orbit in the event that its host planet was responsible for ejecting the hypothetical planet, an incident which would have caused significant disturbance to each moon's original orbit. Ultimately, they found that Jupiter is capable of ejecting the fifth giant planet while retaining a moon with the orbit of Callisto. On the other hand, it would have been very difficult for Saturn to do so because Iapetus would have been excessively unsettled, resulting in an orbit that is difficult to reconcile with its current trajectory.
JUPITER'S GREAT RED SPOT IS SHRINKING
Jupiter's famed Great Red Spot is getting smaller. New images released this week from the Hubble telescope confirm that the Great Red Spot continues to shrink and become more circular, as it has been doing for years. The Great Red Spot is a monstrous storm, with wind speeds of up to 150 m/s (340 mph). The storm is about 150 miles smaller in diameter than it was last year. Although that seems like a lot, the Spot is still about 10,000 miles in diameter. Of course there is no way of knowing whether it will continue to shrink or even ultimately to disappear. The most likely case is that it will stabilize at a smaller size than it is now. It has existed since at least the late 1850s and was much bigger then, and is likely to be the same feature as was reported by a number of observers in the seventeenth century, starting with Hooke in 1664. The Great Red Spot is more orange than red these days, and its core, which typically has a more intense colour, is less distinct than it used to be.
CASSINI SWEEPS PAST ENCELADUS
The Cassini probe has made a close fly-by of Enceladus, an ice-rich moon of Saturn. It swept by, just 50 km above the moon's surface, in a final attempt to ascertain the chemistry of jets spewing from the south pole. Scientists say that Enceladus has an ocean beneath its icy crust. The conditions in that global body of liquid water could be benign enough to support microbial organisms. Cassini will attempt to detect molecular hydrogen, which would be a strong signal that hot vents exist on the rocky ocean floor. Such vent systems on the Earth are known to provide the fundamental energy and nutrient requirements for some deep-sea ecosystems. At those locations, water is drawn into the rock bed, heated and saturated with minerals, before then being ejected back upwards. Bacteria thrive in that environment, establishing a food web that supports a chain to more complex organisms. Whether any such process is going on inside Enceladus is just speculation for now. The amount of any hydrogen emission may allow an estimate to be made of how much hydrothermal activity is actually occurring on the sea floor — with implications for the amount of energy available.
Cassini is entering the final stages of its mission to the Saturnian system, which began with its insertion into orbit around the planet in 2004 July. Since then it has made repeated passes of the major moons, to image them and to characterize their make-up and environment. The latest visit to Enceladus is one of the very closest. Indeed, Cassini will never again get so near to the moon's surface. In December, it will venture to within 5,000 km, but thereafter it will fly no closer than 22,000 km. Previous detections by the probe's instruments have already identified salts and organic molecules in the icy spray. Key indicators of hidden vent activity include the presence in the plumes of silica particles and methane. Molecular hydrogen would be a key find — an independent line of evidence for hydrothermal activity. It would support the notion that a process known as serpentinization was in play. That process sees rocks rich in iron and magnesium minerals react with water, and incorporate water molecules into their crystal structure. On the Earth, some micro-organisms are able to use the hydrogen by-product from serpentinization as an energy source to drive their metabolism. Next year, Cassini will begin a series of manoeuvres to put itself in orbits that take it high above, and through, Saturn's rings. Then, in 2017, once the probe's fuel has all but run out, ground controllers will command the spacecraft to plunge into the planet's atmosphere, where it will be destroyed.
PLUTO'S MOON KEREBOS SHOWS ITSELF
Kerberos appears to be smaller than scientists expected and has a highly reflective surface, contrary to opinions before the Pluto fly-by in July. The new data, downlinked from the New Horizons spacecraft on October 20, show that Kerberos appears to have a double-lobed shape, with the larger lobe approximately 8 km and the smaller lobe approximately 5 km across. Science-team members speculate from its unusual shape that Kerberos could have been formed by the merger of two smaller objects. The reflectivity of Kerberos' surface is similar to that of Pluto's other small moons (approximately 50%) and strongly suggests that Kerberos, like the others, is coated with rather clean water ice. Before the New Horizons encounter with Pluto, researchers had used Hubble images to try to determine the mass of Kerberos by measuring its gravitational influence on its neighbouring moons. That influence was surprisingly strong, in relation to how faint Kerberos is. The scientists theorized that Kerberos was relatively large and massive, appearing faint only because its surface was covered in dark material. But the small, bright-surfaced Kerberos now revealed in the new images shows that that idea was mistaken, for reasons that are not yet understood. The predictions were nearly spot-on for the other small moons, but not for Kerberos. The new results may lead to a better understanding of Pluto's fascinating satellite system.
NEW COMPONENT OF MILKY WAY FOUND
Astronomers using the VISTA telescope at the Paranal Observatory have discovered a previously unknown component of the Milky Way. By mapping the locations of a lot of Cepheid variable stars a disc of young stars buried behind thick dust clouds in the central bulge has been found. The public survey is using the VISTA telescope to take multiple images at different times of the central parts of the galaxy at infrared wavelengths. It is discovering huge numbers of new objects, including variable stars, clusters and exploding stars. A team of astronomers has now used data from the survey, taken between 2010 and 2014, to make a remarkable discovery — a previously unknown component of our home galaxy, the Milky Way. Astronomers found 655 candidate Cepheid variables. Such stars expand and contract periodically, taking anything from a few days to months to complete a cycle and changing significantly in brightness as they do so. The time taken for a Cepheid to brighten and fade again is longer for those that are brighter and shorter for the dimmer ones. That remarkably precise relationship, which was discovered in 1908 by American astronomer Henrietta Swan Leavitt, makes the study of Cepheids one of the most effective ways of measuring the distances to, and mapping the positions of, distant objects in the Milky Way and beyond.
But there is a catch — Cepheids are not all the same. They come in two main classes, one much younger than the other. Out of their sample of 655 the team identified 35 stars as belonging to a sub-group called classical Cepheids — young bright stars, very different from the usual, much older, residents of the central bulge of the Milky Way. The team gathered information on the brightness and pulsation period, and deduced the distances of the 35 classical Cepheids. Their pulsation periods, which are closely linked to their age, revealed their surprising youth. All of the 35 classical Cepheids discovered are less than 100 million years old. The youngest may even be only around 25 million years old, although the possible presence of even younger and brighter ones cannot be excluded. The ages of those classical Cepheids provide solid evidence that there has been a previously unconfirmed, continuous supply of newly formed stars into the central region of the Milky Way over the last 100 million years. But that was not the only remarkable discovery from the survey: mapping the Cepheids that they discovered, the team traced an entirely new feature in the Milky Way — a thin disc of young stars across the Galactic bulge. That new component of our home galaxy had been invisible to previous surveys as it is buried behind thick clouds of dust. Further investigations are now needed to assess whether the Cepheids there were born close to where they are now, or whether they originated further out. Understanding their fundamental properties, interactions, and evolution may help in the quest to understand the evolution of the Milky Way, and the process of galaxy evolution as a whole.
HUBBLE OBSERVES BIG-BANG FRONTIERS
ESA/Hubble Information Centre
Observations by the Hubble telescope have taken advantage of gravitational lensing to reveal the largest sample of the faintest and earliest known galaxies in the Universe. Some of them formed just 600 million years after the Big Bang and are fainter than any other galaxy yet uncovered by Hubble. The team has determined, for the first time with some confidence, that those small galaxies were vital to creating the Universe that we see today. Over 250 tiny galaxies were found — one of the largest samples of dwarf galaxies yet to be discovered at those epochs. The light from them took over 12 billion years to reach the telescope, allowing the astronomers to look back in time to when the Universe was still very young. Although impressive, the number of galaxies found at that early epoch is not the only remarkable breakthrough. The faintest galaxies detected in the Hubble observations are fainter than any others previously seen in the deepest Hubble observations. By looking at the light coming from the galaxies the team discovered that the accumulated light emitted by the galaxies could have played a major role in one of the most mysterious periods of the Universe's early history — the epoch of re-ionization. Re-ionization started when the thick fog of hydrogen gas that cloaked the early Universe began to clear. Ultraviolet light was then able to travel over large distances without being blocked, and the Universe became transparent to ultraviolet light.
By observing the ultraviolet light from the galaxies found in this study the astronomers were able to calculate whether they were in fact some of the galaxies involved in the process. The team considers that the smallest and most abundant of the galaxies in the study could be the major actors in keeping the Universe transparent. By doing so, they have established that the epoch of re-ionization — which ends at the point when the Universe is fully transparent — came to a close about 700 million years after the Big Bang. If astronomers took into account only the contributions from bright and massive galaxies, they found that they were insufficient to re-ionize the Universe. They also needed to add in the contribution of a more abundant population of faint dwarf galaxies. To make those discoveries, the team utilized the deepest images of gravitational lensing made so far in three galaxy clusters, which were taken as part of the Hubble 'Frontier Fields' programme. Those clusters generate immense gravitational fields capable of magnifying the light from faint galaxies that lie far behind the clusters themselves. That makes it possible to search for, and study, the first generation of galaxies in the Universe. Clusters in the Frontier Fields act as powerful natural telescopes and unveil faint dwarf galaxies that would otherwise be invisible. Hubble remains unrivalled in its ability to observe the most distant galaxies.
COMMON CHEMICAL MAKEUP AT LARGEST COSMIC SCALES
NASA/Goddard Space Flight Center
A new survey of hot, X-ray-emitting gas in the Virgo galaxy cluster shows that the elements needed to make stars, planets and people were evenly distributed across millions of light-years early in cosmic history, more than 10 billion years ago. The Virgo cluster, located about 54 million light-years away, is the nearest galaxy cluster and the second-brightest in X-rays. The cluster is home to more than 2,000 galaxies, and the space between them is filled with a diffuse gas so hot that it glows in X-rays. Using Japan's Suzaku X-ray satellite, astronomers made observations of the cluster along four arms extending up to 5 million light-years from its centre. Heavier chemical elements from carbon on up are produced and distributed into interstellar space by stars that explode as supernovae at the ends of their lifetimes. That chemical dispersal continues at progressively larger scales through other mechanisms, such as galactic outflows, interactions and mergers with neighbouring galaxies, and stripping caused by a galaxy's motion through the hot gas that fills galaxy clusters. Supernovae fall into two broad classes. Stars born with more than about eight times the Sun's mass collapse under their own gravity and explode as core-collapse supernovae. White-dwarf stars may become unstable through interactions with a nearby star and explode as so-called Type-Ia supernovae. Those different classes of supernovae produce different chemical compositions. Core-collapse supernovae mostly scatter elements ranging from oxygen to silicon,while white-dwarf explosions release predominantly heavier elements, such as iron and nickel. Surveying the distribution of those elements over a vast volume of space, such as a galaxy cluster, helps astronomers reconstruct how, when, and where they were produced. Once the chemical elements made by supernovae are scattered and mixed into interstellar space, they become incorporated into later generations of stars.
The overall composition of a large volume of space depends on the mix of supernova types contributing to it. For example, accounting for the overall chemical makeup of the Sun and Solar System requires a mix of roughly one Type-Ia supernova for every five core-collapse explosions. One way to think about that is that we are looking for the supernova recipe that produced the chemical makeup we see on much larger scales, and comparing it with the recipe for our own Sun. In an earlier study, Suzaku data showed that iron was distributed uniformly throughout the Perseus cluster of galaxies, but information about lighter elements mainly produced by core-collapse supernovae was unavailable. The Virgo Cluster observations supply the missing ingredients. The team has detected iron, magnesium, silicon and sulphur all the way across a galaxy cluster for the first time. The elemental ratios are constant throughout the entire volume of the cluster and roughly consistent with the composition of the Sun and most of the stars in our own Galaxy. Because galaxy clusters cover enormous volumes of space, astronomers can use one example to extrapolate the average chemical content of the Universe. The study shows that the chemical elements in the cosmos are well mixed, showing little variation on the largest scales. The same ratio of supernova types — the same recipe — thought to be responsible for the Solar System's make-up was at work throughout the Universe. That probably happened when the Universe was between 2 and 4 billion years old, a period when stars were being formed at the fastest rate in cosmic history. That implies that elements so important to life on Earth are available, on average, in similar relative proportions throughout the bulk of the Universe. In other words, the chemical requirements for life are common throughout the cosmos. Launched in 2005, Suzaku operated for 10 years — five times its target lifespan — to become the longest-functioning Japanese X-ray observatory. On Aug. 26, JAXA announced the end of the mission owing to the deteriorating health of the spacecraft. Its successor, ASTRO-H, Japan's sixth X-ray astronomy satellite, is expected to be launched in 2016.
Bulletin compiled by Clive Down
(c) 2015 the Society for Popular Astronomy
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