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February 7, 2016 at 3:52 pm #8786Anonymous
The SOCIETY for POPULAR ASTRONOMY
Electronic News Bulletin No. 415 2016 February 7
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/
INTENSIFYING COSMIC RAYS
For the past year, neutron monitors around the Arctic Circle have sensed an increasing intensity of cosmic rays. Polar latitudes are a good place to make such measurements, because the Earth's magnetic field funnels and concentrates cosmic radiation there. It turns out that the Earth's poles are not the only places where cosmic rays are intensifying. Scientists have been launching helium balloons into the stratosphere to measure radiation, and they find the same trend over California. Cosmic rays, which are accelerated in all directions (including towards the Earth) by distant supernova explosions and other violent events, are an important form of space weather. They can seed clouds, trigger lightning, and penetrate commercial aeroplanes. Indeed, measurements show that someone flying back and forth across the Atlantic, just once, can absorb as much ionizing cosmic radiation as from 2 to 5 dental X-rays. Likewise, cosmic rays can affect mountain climbers, high-altitude drones, and astronauts on the International Space Station. That type of radiation is modulated by solar activity. Solar storms and CMEs tend to sweep aside cosmic rays, making it more difficult for cosmic rays to reach the Earth. On the other hand, low solar activity allows an extra dose of cosmic rays to reach our planet. Indeed, the ongoing increase in cosmic-ray intensity is probably due to a decline in the solar cycle. Solar Maximum has passed and we are heading toward a new Solar Minimum. Forecasters expect solar activity to drop sharply in the years ahead, and cosmic rays are likely to increase accordingly.
MOON FORMED BY HEAD-ON COLLISION
University of California – Los Angeles
UCLA geochemists and colleagues have reported their conclusion that the Moon was formed by a violent, head-on collision between the early Earth and a 'planetary embryo' called Theia approximately 100 million years after the Earth formed. Scientists had already known about that collision, which occurred almost 4.5 billion years ago, but many thought the Earth collided with Theia (pronounced THAY-eh) at an angle of 45 degrees or more — a powerful side-swipe. New evidence substantially strengthens the case for a head-on impact (the idea of a collision of that character was initially proposed in 2012). The researchers analyzed seven rocks brought to the Earth from the Moon by the Apollo 12, 15 and 17 missions, as well as six volcanic rocks from the Earth's mantle — five from Hawaii and one from Arizona. The key to reconstructing the impact was a chemical signature revealed in the rocks' oxygen atoms. (Oxygen makes up 50% of the rocks' weight.) More than 99.9% of the Earth's oxygen is O-16, so called because each atom contains eight protons and eight neutrons. But there also are small quantities of heavier oxygen isotopes: O-17, which has one extra neutron, and O-18, which has two extra neutrons. The Earth, Mars and other planetary bodies in the Solar System have each a unique ratio of O-17 to O-16 — each one a distinctive 'fingerprint'. In 2014, a team of German scientists reported that the Moon also has its own unique ratio of oxygen isotopes, different from the Earth's. The new research finds that that is not the case. The fact that oxygen in rocks on the Earth and the Moon share chemical signatures is very telling. Had the Earth and Theia collided in a glancing side blow, the vast majority of the Moon would have been made mainly of Theia, and the Earth and Moon should have different ratios of the oxygen isotopes. A head-on collision, however, would be likely to have resulted in similar chemical compositions for the Earth and the Moon.
Theia was thoroughly mixed into both the Earth and the Moon, and evenly dispersed between them. That explains why we do not see different signatures of Theia in the Moon and the Earth. Theia, which did not survive the collision (except that it now makes up large parts of the Earth and Moon) was growing and probably would have become a planet if the crash had not occurred. The team believes that the planet was approximately the same size as the Earth; others believe it was smaller, perhaps more similar in size to Mars. Another interesting question is whether the collision with Theia removed any water that the early Earth may have contained. After the collision –perhaps tens of millions of year later — small asteroids probably hit the Earth, including ones that may have been rich in water. Collisions of growing bodies occurred very frequently back then, although Mars avoided large collisions.
PLANET IN HUGE ORBIT AROUND STAR
A team of astronomers in the UK, USA and Australia has found that a planet, until now thought to be a free-floating or lonely planet, is in a huge orbit around its star. The object, designated as 2MASS J2126, is about 7000 times as far from its star as the Earth is from the Sun. In the last five years a number of free-floating planets has been found. They are gas-giant worlds like Jupiter that lack the mass for the nuclear reactions that make stars shine, so they cool and fade over time. Measuring the temperatures of such objects is relatively straightforward, but it depends on both mass and age. That means that astronomers need to find out how old they are, before they can find out if they are lightweight enough to be planets or if they are more massive 'failed stars' known as brown dwarfs. US-based researchers found 2MASS J2126 in an infrared sky survey, flagging it as a possible young and hence low-mass object. In 2014 Canadian researchers identified it as a possible member of a 45-million-year-old group of stars and brown dwarfs known as the Tucana-Horologium Association. That made it young and low enough in mass to be classified as a free-floating planet. In the same region of the sky, TYC 9486-927-1 is a star that had been identified as being young, but not as a member of any known group of young stars. Until now no one had suggested that TYC 9486-927-1 and 2MASS J2126 were in any way linked.
UK astronomers have spent the last few years searching for young stars with companions in wide orbits. As part of the work, the team looked through lists of known young stars, brown dwarfs and free-floating planets to see if any of them could be related. They found that TYC 9486-927-1 and 2MASS J2126 are moving through space together and are both about 32 parsecs (104 light-years) from the Sun, implying that they are associated. That is the widest planet system found so far, and both the members of it have been known for eight years, but nobody had recognized the link between them before. When they looked in more detail, the team members were not able to confirm that TYC 9486-927-1 and 2MASS J2126 are members of any known group of young stars. Membership in a group of young stars is great for establishing an age, but when astronomers can not use that method they need to resort to another. The team then looked at the spectrum of the star to measure the strength of a feature arising from the element lithium. Lithium is destroyed early on in a star's life, so the more lithium it has, the younger it is likely to be. TYC 9486-927-1 has stronger signatures of lithium than the stars of the the Tucana-Horologium Association but weaker signatures than a group of 10-million-year-old stars, implying an age between the two. On the basis of such an age the team was able to estimate the mass of 2MASS J2126, finding it to be between 11.6 and 15 times the mass of Jupiter. That placed it on the boundary between planets and brown dwarfs. It means that 2MASS J2126 has a similar mass, age and temperature to one of the first planets directly imaged around another star, Beta Pictoris b. Compared to Beta Pictoris b, 2MASS J2126 is more than 700 times further away from its host star, but how such a wide planetary system could form and survive remains an open question. At such an enormous distance it takes roughly 900,000 years to complete one orbit, so it has probably completed fewer than fifty orbits over its existence.
BRIGHTEST ULTRA-METAL-POOR STAR YET DISCOVERED
University of Notre Dame
A team of researchers has observed the brightest ultra-metal-poor star ever discovered. The star is a rare relic from the Milky Way's formative years. As such, it offers astronomers a precious opportunity to explore the origin of the first stars that sprang to life within our Galaxy and the Universe. The team used two ESO telescopes in Chile to discover the star, named 2MASS J18082002-5104378. Follow-up observations with the Very Large Telescope discovered that, unlike younger stars such as the Sun, that star shows an unusually low abundance of what astronomers call metals — elements heavier than hydrogen and helium. It is so devoid of such elements that it is known as an ultra-metal-poor star. Although thought to be ubiquitous in the early Universe, metal-poor stars are now a rare sight within both the Milky Way and other nearby galaxies. Metals are formed during nuclear fusion within stars, and are spread throughout the interstellar medium when some of those stars grow old and explode. Subsequent generations of stars therefore form from increasingly metal-rich material. Metal-poor stars, however, were formed from the unpolluted environment that existed shortly after the Big Bang. Exploring stars such as 2MASS J18082002-5104378 may unlock secrets about their formation, and show what the Universe was like at its very beginning.
GIGANTIC CLOUD RETURNS TO OUR GALAXY
Space Telescope Science Institute (STScI)
Hubble Space Telescope astronomers are finding that the old adage 'what goes up must come down' applies even to an immense cloud of hydrogen gas outside our Milky Way galaxy. The invisible cloud is plummeting toward our Galaxy at nearly 700,000 miles per hour. Though hundreds of enormous, high-velocity gas clouds whizz round the outskirts of our Galaxy, this so-called 'Smith Cloud' is unique because its trajectory is well known. New Hubble observations suggest that it was launched from the outer regions of the Galactic disc around 70 million years ago. The cloud was discovered in the early 1960s by doctoral astronomy student Gail Smith, who detected the radio waves emitted by its hydrogen. The cloud is on a return collision course and is expected to plough into the Milky Way's disc in about 30 million years. Astronomers believe that, when it does, it will ignite a spectacular burst of star formation, perhaps providing enough gas to make 2 million stars. Astronomers have measured the comet-shaped region of gas to be 11,000 light-years long and 2,500 light-years across. If the cloud could be seen in visible light, it would span the sky with an apparent diameter 30 times greater than the size of the full Moon. Astronomers long thought that the Smith Cloud might be a failed, starless galaxy, or gas falling into the Milky Way from intergalactic space. If either of those possibilities were true, the cloud would contain mainly hydrogen and helium, not the heavier elements made by stars. But if it came from within the Galaxy, it would contain more of the heavier elements.
The team used Hubble to measure the Smith Cloud's chemical composition for the first time They observed the ultraviolet light from the bright cores of three active galaxies that reside billions of light-years beyond the cloud. Using Hubble's 'Cosmic Origins' spectrograph, they looked at light that had passed through the cloud, in particular for absorption lines of sulphur. Sulphur is suggested to be a good gauge of the abundance of heavier elements in general. The astronomers found that the Smith Cloud is as rich in sulphur as the Milky Way's outer disc, a region about 40,000 light-years from the Galactic Centre (about 15,000 light-years farther out than the Solar System). That means that the Smith Cloud was enriched by material from stars, which would not have happened if it were pristine hydrogen from outside the Galaxy, or if it were the remnant of a failed galaxy devoid of stars. Instead, the cloud appears to have been ejected from within the Milky Way and is now boomeranging back. Though that seems to settle the question of the Smith Cloud's origin, it raises new questions: how did the cloud get to where it is now; what cataclysmic event could have catapulted it from the Milky Way's disc; and how did it remain intact? No answers are yet available.
'WOW!' SIGNAL THEORY
Almost 40 years ago, we received a mysterious signal from space. The signal lasted for 72 seconds and it was so unusual that it was dubbed the Wow! Signal, owing to the word scrawled by its discoverer. It has been puzzling scientists ever since. Several explanations from unusual phenomena, transient events, and even aliens have been put forward. Now Paris, a professor of astronomy at St Petersburg College in Florida, thinks that the signal might have originated from one or two passing comets. The objects were not known at the time, but their orbit and position in 1977 was remarkably close to the location that the Wow! signal seemed to have come from. The Big Ear telescope in Ohio, which made the original discovery, had a fixed field of view, so it depended on the Earth's rotation to scan the sky; it could observe any given area for only 72 seconds. On 1977 August 15 it was looking in the direction of the Chi Sagittari star group when it detected the signal. It was clearly of extra-terrestrial origin and definitely worth follow-up observations. The same region has been observed several times since, but the observation has never been replicated. For that reason, some researchers suggested that it was a one-off event, something passing in the area of the sky at the time. That made Paris think of the comets 266P/Christensen and P/2008 Y2 (Gibbs).
The signal was observed at 1420 MHz. The telescope used that frequency to observe neutral hydrogen, which can emit at that wavelength. Paris claims that the two comets release a lot of water and the UV light from the Sun breaks the water, liberating the hydrogen. Some researchers are sceptical. Comets would have to release a significant amount of hydrogen to produce a signal as strong as the Wow! Signal. The hypothesis must be tested before it is ruled out, and Paris will get his chance in the next few years. Comet 266P/Christensen will be back in that region in 2017, and P/2008 Y2 (Gibbs) in 2018. By studying their radio emission and how quickly they move in the sky, astronomers should be able to tell if either of them could really have been the source of the Wow! signal.
JAMES WEBB SPACE TELESCOPE
The successor to the Hubble Space Telescope is reaching some key milestones in its preparation for launch in 2018. Engineers are about to complete the assembly of the primary mirror surface on the James Webb Space Telescope. They are also finishing the final deep-chill calibration tests on the observatory's four instruments. The US space-agency-led project is now on track to make rapid progress in the coming months. The major components of JWST, which have been years in the design and fabrication phase, will at last be integrated into their flight configuration. With a time margin still in the programme to cope with any unexpected problems, everything currently remains on course for a 2018 October lift-off on a European Ariane rocket. Webb is a joint venture between NASA and its European and Canadian counterparts. It will go in search of the very first stars to shine in the Universe. To achieve that ambition, it will deploy a 6.5-m mirror, giving the observatory roughly seven times the light-collecting area of Hubble. And allied to instruments that are sensitive in the infrared, Webb will be tuned to detect the faint, 'stretched' glow of objects that originally shone more than 13.5 billion years ago.
SPACE MISSIONS FOR 2016
2015 was the year we saw Pluto and found water on Mars. In 2016, we may be going to learn how the planets were made. The European Space Agency's ExoMars rover will land on Mars, Osiris-REX will be launched towards the asteroid, and Rosetta will smash into comet 67P. JAXA, the Japanese Space Agency, is launching the X-ray telescope ASTRO-H this month. X-Rays are produced when cosmic matter is heated to millions of degrees. By looking at them from space, we can pick up data impossible to gather from the ground. The satellite has four sensor systems, allowing it to measure hard and soft X-rays and gamma rays, and to perform X-ray spectroscopy. ASTRO-H will open up windows into the distribution of dark matter in galaxies, and the large-scale structure of the Universe. Another mission this year is going to look into the Solar System's formation as a whole by looking at Jupiter. NASA's Juno spacecraft will arrive at the Jovian system on July 5. Galileo was in orbit around Jupiter from 1995 to 2003, and we have not had anything in orbit since. We are long overdue for a dedicated Jupiter mission, particularly one that will measure something we do not know about — the amount of water in Jupiter's atmosphere. This seems esoteric, but it is actually going to help scientists with the major question of which planet-formation theory may be correct, or tell us if we need an entirely new theory by telling us where the water on Earth came from. If Juno finds that there is little water in Jupiter's atmosphere, scientists will probably conclude that icy bodies like asteroids from the distant Kuiper Belt brought water as ice to the rocky inner planets. And because Jupiter is our best example of a giant planet, knowing more about its formation may help us understand the planets found around other stars.
ANTARCTIC FUNGI SURVIVE MARTIAN CONDITIONS
FECYT – Spanish Foundation for Science and Technology
European scientists have gathered tiny fungi that take shelter in Antarctic rocks and sent them to the International Space Station. After 18 months on board in conditions similar to those on Mars, more than 60% of their cells remained intact, with stable DNA. The results provide new information for the search for life on Mars. Lichens from the Sierra de Gredos (Spain) and the Alps (Austria) also travelled into space for the same experiment. The McMurdo Dry Valleys, in the Antarctic Victoria Land, are considered to be the most similar earthly equivalent to Mars. They make up one of the driest and most hostile environments on our planet, where strong winds scour away even snow and ice. Only so-called cryptoendolithic micro-organisms, capable of surviving in cracks in rocks, and certain lichens, can withstand such harsh climatological conditions. A few years ago a team of European researchers travelled to those valleys to collect samples of two species of crypto-endolithic fungi, Cryomyces antarcticus and Cryomyces minteri. The aim was to send them to the International Space Station (ISS) for them to be subjected to Martian conditions and space and to observe their responses.
The tiny fungi were placed in cells (1.4 cm in diameter) on a platform for experiments known as EXPOSE-E, developed by the European Space Agency to withstand extreme environments. The platform was sent in the Space Shuttle Atlantis to the ISS and placed outside the Columbus module by an astronaut. For 18 months half of the Antarctic fungi were exposed to Mars-like conditions. More specifically, that is an atmosphere with 95% CO2, 1.6% argon, 0.15% oxygen, 2.7% nitrogen and 370 parts per million of H2O, and a pressure of 1,000 pascals. Through optical filters, samples were subjected to ultra-violet radiation as if on Mars and others to lower radiation, including separate control samples. The most relevant outcome was that more than 60% of the cells of the endolithic communities studied remained intact after 'exposure to Mars', or rather, the stability of their cellular DNA was still high.
Bulletin compiled by Clive Down
(c) 2016 the Society for Popular Astronomy
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