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May 29, 2016 at 10:46 am #8888Anonymous
The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 423 2016 May 29
Here is the latest round-up of news from the Society for Popular Astronomy. The SPA is arguably Britain's liveliest astronomica lsociety, 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/
RESEARCHERS FIND ROCKS 4.5 BILLION YEARS OLD
A recent study has found two 'birthmarks' in the Earth's mantle,consisting of silicate material that formed when the planet was lessthan 50 million years old. Researchers found clear signatures of a distinctive material in two completely separate locations on the globe— Baffin Bay in the north of Canada and the Ontong Java Plateau inthe western Pacific Ocean. They give the first clear indication that portions of the mantle that were formed during the Earth's primary accretion period still exist today. Scientists believe that the Earth grew to its current size through the accretion of material from collisions with bodies of increasing size over several tens of millions of years early in the history of the Solar System. The last and most massive of those impacts was a collision between the proto-Earth and a planetoid approximately the size of Mars, that resulted in the formation of our Moon. Scientific consensus had long held itunlikely that any vestiges of rock from the earliest period of the Earth's history would still survive. It was thought that the physical mixing and internal heat caused by the many collisions with otherSolar-System bodies would have homogenized material from the Earth'searly mantle. However, that view began to change when findings by researchers in 2012 indicated that some material from the primitive mantle continued to exist until at any rate 2.8 billion years ago.
The researchers noted that “Four and a half billion years of geological activity have overprinted much of the evidence for the processes involved in Earth's formation and initial chemical differentiation.” However, they write that high-precision measurements of the ratios of different isotopes of specific elements can “provide a view of events that occurred during the first few tens to hundreds of million years of Earth history, using short-lived radionuclides [unstable forms of chemical elements that decay radioactively] that were present when Earth formed.” The team's identification of primitive mantle material was based on its detection of an over-abundance of an isotope of tungsten. The radioactive element hafnium decays into the tungsten. 182-hafnium is an isotope of the element that was present at the time that the Solar System formed, but is no longer present on the Earth today. The decay of 182-hafnium into 182-tungsten is so rapid that variations in the abundance of 182-tungsten relative to other isotopes of tungsten can be due only to processes that occurred very early in the history of the Solar System.
EARTH'S MAGNETIC FIELD IS CHANGING
Anyone watching a compass needle point steadily north might supposethat Earth's magnetic field is constant, but it is not. The positions of the magnetic poles routinely move, as much as 40 km a year.Moreover, the global magnetic field has weakened by 10% since the 19th century. A new study by ESA's 'Swarm' satellites reveals that changesmay be happening even more quickly than was previously thought. Swarmis a trio of satellites equipped with vector magnetometers capable of sensing the Earth's magnetic field all the way from orbital altitudes down to the edge of the planet's core. They are expected to continue operations at least until 2017, and possibly beyond. Their data,combined with observations from the CHAMP and Oersted satellites, show clearly that the field has weakened by about 3.5% at high latitudes over North America, while it has strengthened by about 2% over Asia. The field in the region where it is weakest — the South Atlantic Anomaly — has moved steadily westward and weakened further by about2%. Those changes have occurred just since 1999.
The Earth's magnetic field protects us from solar storms and cosmic rays. Less magnetism means that more radiation can penetrate to lowlevels. Indeed, high-altitude balloons routinely detect increasing levels of cosmic rays over California. Perhaps the ebbing magnetic field over North America contributes to that trend. As remarkable as those changes sound, they are mild compared to what the Earth's magnetic field has done in the past. Sometimes the field reverses completely, with the north and the south poles exchanging places.Such reversals, recorded in the magnetism of ancient rocks, are unpredictable. They come at irregular intervals averaging about 300,000 years, but the last one was 780,000 years ago, so it may seem that we are overdue for another.
JUPITER HIT BY 6 FIREBALL IMPACTS PER YEAR
Jupiter is hit by an average of 6.5 objects per year that create impacts large enough to be visible from the Earth, according to preliminary results from a worldwide campaign by amateur astronomers. Meteors impacting Jupiter's upper atmosphere can create spectacular fireballs, such as one observed by amateur astronomers on March 17.That was the fourth fireball observed on Jupiter serendipitously by amateur astronomers since 2010. Groups of amateurs worldwide have coordinated efforts to obtain improved estimates of the number of small bodies around Jupiter and how they interact with the planet. Marc Delcroix, who coordinates a 60-strong group, said, “Dramatic impacts with Jupiter can be captured with standard amateur equipment and analysed with easy-to-use software.” But to get a good estimate of how often such events occur, we need observers around the world who are willing to collaborate to create a programme of more or less continuous monitoring of Jupiter. It takes time and commitment –observations of no impacts are just as important as detecting a fireball. The new estimate of 6.5 impacts a year of comparable-size objects lies at the lower end of previous estimates of impacts.
EUROPA'S OCEAN MAY HAVE EARTH-LIKE CHEMICAL BALANCE
A new study modelling conditions in the ocean of Jupiter's moon Europa suggests that the necessary balance of chemical energy for life could exist there, even if the moon lacks volcanic hydrothermal activity.Europa is strongly believed to hide a deep ocean of salty liquid water beneath its icy shell. Whether it has the raw materials and chemical energy in the right proportions to support biology is a topic of considerable interest. The answer may hinge on whether Europa has environments where chemicals are matched in the right proportions to power biological processes. Life on Earth exploits such niches. In a new study, scientists at the Jet Propulsion Laboratory in Pasadena compared Europa's potential for producing hydrogen and oxygen with that of the Earth, through processes that do not directly involve vulcanism. The balance of the two elements is an indicator of the energy available for life. The study found that the amounts would be comparable in scale; on both worlds, oxygen production is about 10 times higher than hydrogen production. The work draws attention to the ways in which Europa's rocky interior may be much more complex and possibly Earthlike than people might think. Scientists are studying an alien ocean using methods developed to understand the movement of energy and nutrients in the Earth's own systems. The cycling of oxygen and hydrogen in Europa's ocean will be a major driver for the chemistry and any life there, just as it is on Earth. Ultimately,researchers want also to understand the cycling of life's other majo relements in the ocean: carbon, nitrogen, phosphorus and sulphur.
As part of their study, the researchers calculated how much hydrogen could potentially be produced in Europa's ocean as sea water reactswith rock, in a process called serpentinization. In that process,water percolates into spaces between mineral grains and reacts withthe rock to form new minerals, releasing hydrogen in the process. The researchers considered how cracks in Europa's sea floor may open upover time, as the moon's rocky interior continues to cool following its formation millions of years ago. New cracks expose fresh rock to sea water, where more hydrogen-producing reactions can take place. Inthe Earth's oceanic crust, such fractures are believed to penetrate to a depth of 5 to 6 kilometres. On present-day Europa, the researchers expect that water could reach as deep as 25 kilometres into the rocky interior, driving the key chemical reactions throughout a deeper fraction of Europa's sea floor. The other half of Europa's chemical-energy-for-life equation would be provided by oxidants — oxygen andother compounds that could react with the hydrogen — being cycled into the ocean from the icy surface above. Europa is bathed in radiation from Jupiter, which splits water-ice molecules to release those elements. Scientists have inferred that Europa's surface is being cycled back into its interior, which could carry oxidants into the ocean. The oxidants from the ice are like the positive terminal of a battery, and the chemicals from the sea floor, called reductants,are like the negative terminal. Whether or not life and biological processes complete the circuit is part of what motivates the exploration of Europa. Europa's rocky neighbouring moon, Io, is themost volcanically active body in the Solar System, owing to heat produced by the stretching and squeezing effects of Jupiter's gravity as Io orbits the planet. Scientists have long considered it possible that Europa might also have volcanic activity, as well as hydrothermal vents, where mineral-laden hot water would emerge from the sea floor.Researchers previously speculated that vulcanism is paramount for creating a habitable environment in Europa's ocean. If such activity is not occurring in its rocky interior, the thinking goes, the large flux of oxidants from the surface would make the ocean too acidic andtoxic for life. But actually, if the rock is cold, it is easier to fracture. That allows for a huge amount of hydrogen to be produced by serpentinization that would balance the oxidants in a ratio comparableto that in the Earth's oceans.
ICY COMETS ORBITING SUN-LIKE STAR
University of Cambridge
An international team of astronomers has found evidence of ice and comets orbiting a nearby Sun-like star, which could give a glimpse into how our own Solar System developed. Using data from the Atacama Large Millimetre Array (ALMA), the researchers detected very low levels of carbon monoxide gas around the star, in amounts that are consistent with the comets in the Solar System. The results are a first step in establishing the properties of comet clouds around Sun-like stars just after the time of their birth. Comets are essentially 'dirty snowballs' of ice and rock, sometimes with a tail of dust and evaporating ice trailing behind them, and are formed earlyin the development of stellar systems. They are typically found in the outer reaches of the Solar System, but become most clearly visible when they visit the inner regions. For example, Halley's Comet visits the inner Solar System every 75 years, some take as long as 100,000years between visits, and others only visit once before being thrown out into interstellar space. It has been suggested that when theSolar System was first formed, the Earth was a rocky wasteland,similar to how Mars is today, and that as comets collided with the young planet, they brought many elements and compounds, including water, along with them.
The star in the study that we originally set out to tell you about, before we side-tracked ourselves with that autonomous harangue aboutcomets, HD 181327, has a mass about 30% greater than the Sun's and islocated 160 light-years away in the constellation Pictor. The system is thought to be about 23 million years old. Young systems such as that one are very active, with many collisions taking place between the minor bodies that may be circulating in them. The system has a similar ice composition to our own, so it might mimic how the Solar System looked early in its existence. Using ALMA, the astronomers observed the star, which is surrounded by a ring of dust caused by the collisions of the orbiting bodies. The star may have planets in orbit around it, but they would be impossible to detect with current telescopes. If there are such planets, the only way to detect them would be through direct imaging, which at present is only possible for large planets like Jupiter. In order to detect the possible presence of comets, the researchers used ALMA to search for signatures of gas,since the same collisions which caused the dust ring to form should also cause the release of gas. Until now, such gas has been detected around only a few stars, all substantially more massive than the Sun.Using simulations to model the composition of the system, the research team was able to recognize, in the ALMA data, carbon monoxide gas,albeit at a very low level.
THE SUN AS A STAR
Leibniz Institute for Astrophysics Potsdam (AIP)
Astrophysicists have for the first time measured the rotation periods of stars in a cluster about as old as the Sun and found them to be similar. It turns out that those stars rotate in about 26 days –just like the Sun. The discovery could be held to strengthen what is known as the solar-stellar connection, a principle that underlies some of solar and stellar astrophysics. The principle — that the Sun is a star — was not proved until distances to the nearest stars were measured in the 19th century. It enables us to use the Sun, the only star we can observe in detail, as a possible exemplar for processes occurring on other stars, and conversely, to use other stars to infer the past and future of the Sun. Stellar rotation periods are a key probe of magnetic phenomena on stars. Astronomers working recently on the old open cluster M67, the nearest cluster of solar-aged stars,measured for twenty Sun-like stars the tiny periodic light variations caused by starspots on the stellar surfaces being carried across the discs by rotation. Since the stars concerned are quite old, their starspots are relatively small — similar to spots on the Sun but tiny compared with those on younger stars. The measurements were made with what was formerly known as the Kepler Space Telescope, now re-purposed as 'the K2 mission'.
KEPLER MISSION DISCOVERS 1,284 NEW PLANETS
The Kepler mission has verified 1,284 new planets — the largest single finding of planets to date. Analysis was performed on the Kepler space telescope's 2015 July planet-candidate catalogue, which identified 4,302 potential planets. For 1,284 of the candidates, the probability of being a planet is greater than 99% — the minimum required to earn the status of 'planet'. An additional 1,327candidates are more likely than not to be actual planets, but they do not meet the 99% threshold and will require additional study. Thereare 707 that are more likely to be some other astrophysical phenomena.The analysis also validated 984 candidates previously verified by other techniques. Kepler captures the discrete signals of distant planets — decreases in brightness that occur when planets pass in front of, or transit, their stars. Since the discovery of the first planets outside the Solar System more than 20 years ago, researchers have resorted to a laborious, one-by-one process of verifying suspected planets. This latest announcement, however, is based on a statistical analysis method that can be applied to many planet candidates simultaneously. In the newly-validated batch of planets,nearly 550 could be rocky planets like the Earth, on the basis on their sizes. Nine of them orbit in their respective stars' 'habitable zone' — the range of distances from a star where orbiting planets can have surface temperatures that allow liquid water to exist. With the addition of those nine, 21 exo-planets are now known to be members ofthat group. Of the total of nearly 5,000 planet candidates found to date, more than 3,200 now have been verified, and 2,325 of them were discovered by Kepler. Kepler was launched in 2009, and for four years it monitored 150,000 stars in a single patch of sky. Due to be launched in 2018, the 'Transiting Exoplanet Survey Satellite' will use the same method to monitor 200,000 bright nearby stars and search for planets.
SMALL BLUE GALAXY MAY SHED LIGHT ON BIG BANG
A faint blue galaxy about 30 million light-years away and located in the constellation Leo Minor could shed new light on conditions at thebirth of the Universe. Astronomers recently found that the galaxy,AGC 198691, nicknamed Leoncino or 'little lion', contains the lowest level of heavy chemical elements, or 'metals', ever observed in a gravitationally bound system of stars. Finding the most metal-poorgalaxy might contribute to a quantitative test of the Big Bang. There are few ways to explore conditions at the birth of the Universe, but low-metal galaxies are among the most promising. That is because the currently accepted model of the start of the Universe makes clear predictions about the amount of helium and hydrogen present during the Big Bang, and the ratio of those atoms in metal-poor galaxies provides a direct test of the model. In astronomical parlance, any element other than hydrogen or helium is referred to as a metal. The elemental make-up of metal-poor galaxies is very close to that of the early Universe. To find low-metal galaxies, however, astronomers must look far from home. Our own Milky Way galaxy is a poor source of data, owing to the abundance of heavier elements created over time by stellar processing, in which stars churn out heavier elements through nucleosynthesis and then distribute them back into space when they explode as supernovae. Low metal abundance is a sign that very little stellar activity has taken place.
Leoncino is considered to be a member of the 'local Universe', a region of space within about 1 billion light-years from us and estimated to contain several million galaxies, of which only a small fraction has been catalogued. A galaxy previously recognized to possess the lowest metal abundance was identified in 2005; however, Leoncino has a metal abundance estimated to be 29% lower. Aside from low levels of heavier elements, Leoncino is unique in other ways. A so-called 'dwarf galaxy', it is only about 1,000 light-years in diameter and is composed of several million stars. The Milky Way, by comparison, contains an estimated 200 to 400 billion stars. Leoncino is also blue in colour, owing to a preponderance of recently formed hot stars, but surprisingly dim, with the lowest luminosity level ever observed in a system of its type.
FAINTEST EARLY GALAXY EVER SEEN
University of California – Los Angeles
An international team of scientists has detected the faintest early-Universe galaxy so far recognized. Using the Keck telescope onMauna Kea in Hawaii, the researchers recorded the galaxy as it was13 billion years ago. The discovery could be a step towards answering one of the thorniest questions in astronomy: how the period of time known as the 'cosmic dark ages' ended. The researchers made the discovery through the fortunate effect of gravitational lensing brightening up the incredibly faint object, which was born just after the Big Bang. The detected galaxy was behind a galaxy cluster known as MACS 2129.4-0741, which is massive enough to create three different images of the faint galaxy far behind it. According to the Big Bang theory, the Universe cooled as it expanded. As that happened, protons captured electrons to form hydrogen atoms, which in turn made the Universe opaque to radiation — giving rise to the cosmic dark ages. At some point, a few hundred million years later, the first stars formed, and they started to produce ultraviolet light capable of ionizing hydrogen. Eventually, when there were enough stars, they might have been able to ionize all of the intergalactic hydrogen and create the Universe as we see it now. That process, called cosmic re-ionization, happened about 13 billion years ago, but scientists have so far been unable to determine whether there were enough stars to do it or whether more exotic sources, like gas falling onto super-massive black holes, might have been responsible. Currently, the most likely suspect is stars within galaxies that are too faint to see with our telescopes without gravitational-lensing magnification. This study exploits gravitational lensing to demonstrate that such galaxies do exist, and may thus be a useful step toward solving the problem.
Bulletin compiled by Clive Down (c) 2016 The Society for Popular Astronomy
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