How to Find Faraway Moons
While the number of confirmed extrasolar planets is now approaching 300, the tally of extrasolar moons so far identified is still a rather disappointing zero. Planets beyond our solar system are incredibly challenging to find. Moons are nearly impossible with today's technology, given that they are generally expected to be quite small compared to their parent worlds. Even Earth's moon is invisible on the famous "pale blue dot" image obtained by Voyager 1 from the comparatively small distance of 3.7 billion miles — a photograph taken from well within our solar system. But the search is not impossible, says Darren Williams, associate professor of physics and astronomy at Penn State Erie, the Behrend College. Williams believes a moon in orbit around a known extrasolar planet will also be detectable if we look hard enough with the right techniques. "It will add a periodic component to the combined infrared signal" of the planet-moon system, he said. Why it matters Finding moons is more than just an academic quest to count them up. Planetary satellites can be highly interesting in their own right. It's possible, for example, that life could exist on extrasolar moons, researchers say. And it has been suggested that the ocean tides induced by Earth's moon may have been necessary to create the conditions for life on our planet to begin. At the least, the evolution of life has been affected by our moon's constant tugging. "We certainly owe our present climate stability to the Moon and its stabilizing influence on the spin axis, but I'm not convinced that big moons are a requirement for simple or advanced life," Williams said. "I do think that Earth would have evolved advance life even with greater seasonal extremes, but it may have taken a different evolutionary path." How to find them Williams has modelled an Earth-like planet with moons of varying sizes and concluded that satellites as small as Earth's moon could be detectable in the infrared data, owing to their large surface temperature variations. By studying an extrasolar planet and building up a picture of that world's infrared output, any sizable moons present should be detectable in this way. So far, however, no planet as small as Earth has been detected around another star. But astronomers expect that barrier to be broken soon. Future missions, such as NASA's Terrestrial Planet Finder and The European Space Agency's Darwin, will have the ability to return the valuable data required both for finding other Earths and, Williams figures, some moons. "The present goal is to build instruments capable of seeing something as large as the Earth or possibly Mars. Smaller Mercury- or Titan-sized objects fall below that first-order threshold," Williams said. So could these missions cut to the chase and spot an extrasolar moon directly? "They might, if the light collectors are big enough and if the moons are big enough. It will be easier to see moons that happen to transit the face of a star, such as what the space telescope Kepler will attempt to do starting next year," Williams explained. The space-based Kepler observatory will note dips in starlight caused by planets crossing in front of stars. If the planets are aligned in such a favourable manner, then thinking goes, moons ought to transit the stars too. A similar conclusion is reached by Szabó, Szatmáry, Diveki and Simon in a paper published in Astronomy and Astrophysics in 2005. They conclude that the Kepler mission should identify a few extrasolar moons using this method of detection. Upon reflection Yet even if we are not lucky enough to catch an extrasolar moon in transit, these future space-based planet hunters will be able to do the observational groundwork, in visible light and in the infrared, needed to search for satellites. These planet finders will even be capable of detecting the glint of starlight reflecting off any oceans of liquid water an extrasolar planet may harbor. "Water is extremely dark in the infrared except when the light reflects from the surface at a glancing angle," Williams told SPACE.com. This glint will be most apparent when the planet is in a crescent phase, when the starlight hits the reflective surface at an oblique angle. (Mercury and Venus, as seen from Earth, go through phases similar to our moon. Observations of other planets around distant stars will undergo phasing, too.) Observing such reflections can help map the planet's thermal output and infer the distribution of oceans and continents. Indeed the Mars Express spacecraft is set to observe crescent Earth's ocean reflection this summer and in fall of 2009 to help understand the phenomenon. 17:00 - 9/6/2008 - Comment {yok} - Post CommentNASA Galaxy Hunter: Huge Black Holes Stifle Star Formation
The orbiting observatory surveyed more than 800 nearby elliptical galaxies of various sizes. An intriguing pattern emerged: the more massive, or bigger, the galaxy, the less likely it was to have young stars. Because bigger galaxies are known to have bigger black holes, astronomers believe the black holes are responsible for the lack of youthful stars.
"Supermassive black holes in these giant galaxies create unfriendly places for stars to form," said Dr. Sukyoung K. Yi of Yonsei University in Seoul, Korea, who led the research team. "If you want to find lots of young stars, look to the smaller galaxies." Previously, scientists had predicted that black holes might have dire consequences for star birth, but they didn't have the tools necessary to test the theory. The Galaxy Evolution Explorer, launched in 2003, is well-suited for this research. It is extremely sensitive to the ultraviolet radiation emitted by even low numbers of young stars. Black holes are monstrous heaps of dense matter at the centers of galaxies. Over time, a black hole and its host galaxy will grow in size, but not always at the same rate.
Yi and his collaborators found evidence that the black holes in elliptical galaxies bulk up to a critical mass before putting a stop to star formation. In other words, once a black hole reaches a certain size relative to its host galaxy, its harsh effects become too great for new stars to form. According to this "feedback" theory, the growth of a black hole slows the development of not only stars but of its entire galaxy.
How does a black hole do this? There are two possibilities. First, jets being blasted out of black holes could blow potential star-making fuel, or gas, out of the galaxy center, where stars tend to arise. The second theory relates to the fact that black holes drag surrounding gas onto them, which heats the gas. The gas becomes so hot that it can no longer clump together and collapse into stars.
Other authors of this research include: Drs. Kevin Schawinski, Sadegh Khochfar and Sugata Kaviraj of the University of Oxford, England; Dr. Young-Wook Lee of Yonsei University in Seoul, Korea; Drs. Alessandro Boselli, Jose Donas and Bruno Milliard of the Laboratory of Astrophysics of Marseille, France; Tim Conrow, Drs. Tom Barlow, Karl Forster, Peter G. Friedman, D. Chris Martin, Patrick Morrissey, Mark Seibert, Todd Small and Ted K. Wyder of the California Institute of Technology in Pasadena; Dr. Susan Neff of NASA's Goddard Space Flight Center, Greenbelt, Maryland; Dr. David Schiminovich of Columbia University, N.Y.; Drs. Tim Heckman, Alex Szalay and Luciana Bianchi of Johns Hopkins University, Baltimore, Md.; Dr, Barry Madore of the Observatories of the Carnegie Institute of Washington in Pasadena; and Dr. R. Michael Rich of the University of California, Los Angeles. 09:26 - 25/8/2006 - Comment {yok} - Post CommentSulfur signature changes thoughts on atmospheric oxygen
"The popular model is that there was little oxygen in the Earth's atmosphere before about 2.4 billion years ago," says Dr. Hiroshi Ohmoto, professor of geochemistry and director, Penn State Astrobiology Research Center. "Scientists use the ratio of the various sulfur isotopes as their strongest evidence for atmospheric oxygen."
All isotopes of sulfur behave the same chemically but have slightly different masses. Sulfur has four isotopes. About six years ago, researchers began measuring the abundance of these isotopes and determined their ratios in the natural world. These ratios are called mass dependent isotope fractionation and are the way sulfur fractionates today.
But rocks dating before 2.4 billion years ago have abnormal ratios, or exhibit mass independent fractionation. Generally, scientists attributed this abnormal fractionation to atmospheric chemical reactions. The reaction thought to occur before 2.4 billion years ago is that sulfur dioxide produced by volcanos is separated into native sulfur and sulfuric acids by ultra violet light. Because ozone forms an ultra violet impenetrable shield around the Earth, this reaction could not occur if ozone existed. Ozone is a common component of our atmosphere and is composed of three atoms of oxygen. If the atmosphere has no ozone, it is assumed the atmosphere has no oxygen. Ohmoto, working with Dr. Yumiko Watanabe, research associate, Penn State; Dr. Hiroaki Ikemi, former Penn State post doctoral fellow; and Dr. Simon R. Poulson, former Penn State doctoral student now a professor at University of Nevada, and Dr. Bruce E. Taylor, Geological Survey of Canada, report in today's (Aug. 24) issue of Nature the isotopic, mineralogical and geochemical results of drilling cores recovered by the Archaean Biosphere Drilling Project in the Pilbara Craton, Pilbara, Australia. ABDP is an international project funded largely by the NASA Astrobiology Institute, the Japanese Ministry of Education and Science and the Geological Survey of Western Australia.
The two core segments represent one of the oldest lake sediments -- 2.76 billion years old -- and one of the oldest marine shale sediments -- 2.92 billion years old. Surprisingly, both samples' sulfur isotope ratios fall in the mass-dependent fractionation range and do not show the signal of an oxygenless atmosphere.
"We analyzed the sulfur composition and could not find the abnormal sulfur isotope ratio," said Ohmoto. "This is the first time that sediment that old was found to contain no abnormal sulfur isotope ratio." One possible explanation is that perhaps oxygen levels during that time period fluctuated greatly creating a "yo yo" atmosphere: Going from oxygenless before 3 billion years ago to oxygenated between 3 billion and 2.75 billion years ago and then back to oxygenless from 2.75 billion to 2.4 billion years ago. The researchers suggest that future investigation of different geologic formation could indicate that oxygen fluctuation was even more frequent.
Another explanation could be that the atmosphere contained oxygen as early as 3.8 billion years ago and that mass independent isotope ratios of sulfur occurred because of violent volcanic eruptions and enormous amounts of sulfur dioxide released into the atmosphere. Investigation of ash sediments from recent Mt. Pinatubo eruptions and other major volcanic events show a signature of mass independent isotope ratios of sulfur, while sediment from minor eruption does not.
The photochemical reaction of volcanic sulfur dioxide may not be the only method of creating a mass independent fractionation of sulfur. Reactions between sulfate-rich seawater and organic material in the sediment during the formation of sedimentary rock layers might produce sulfur with mass independent fractionation. If so, the commonly believed linkage between the abnormal sulfur isotope ratios in sediments and an oxygen-free atmosphere must be reevaluated. 09:08 - 25/8/2006 - Comment {yok} - Post Comment
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Supermassive black holes in some giant galaxies create such a hostile environment, they shut down the formation of new stars, according to NASA Galaxy Evolution Explorer findings published in the August 24 issue of Nature. 
Ancient sediments that once resided on a lake bed and the ocean floor show sulfur isotope ratios unlike those found in other samples from the same time, calling into question accepted ideas about when the Earth's atmosphere began to contain oxygen, according to researchers from the U.S., Canada and Japan. 