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The systematic search for possible life outside of Earth is a valid multidisciplinary scientific endeavor.[117] The University of Glamorgan, UK, started just such a degree in 2006,[28] and the American government funds the NASA Astrobiology Institute. However, characterization of non-Earth life is unsettled; hypotheses and predictions as to its existence and origin vary widely, but at the present, the development of theories to inform and support the exploratory search for life may be considered astrobiology's most concrete practical application. Biologist Jack Cohen and mathematician Ian Stewart, amongst others, consider xenobiology separate from astrobiology. Cohen and Stewart stipulate that astrobiology is the search for Earth-like life outside of our solar system and say that xenobiologists are concerned with the possibilities open to us once we consider that life need not be carbon-based or oxygen-breathing, so long as it has the defining characteristics of life. (See carbon chauvinism). Research outcomes[edit] Asteroid(s) may have transported life to Earth. As of 2014, no evidence of extraterrestrial life has been identified. Examination of the Allan Hills 84001 meteorite, which was recovered in Antarctica in 1984 and believed to have originated from Mars, is thought by David McKay, Chief Scientist for Astrobiology at NASA's Johnson Space Center, as well as other scientists, to contain microfossils of extraterrestrial origin; this interpretation is controversial.[118][119][120] Yamato 000593 is the second largest meteorite from Mars found on Earth in 2000. At a microscopic level, spheres are found in the meteorite that are rich in carbon compared to surrounding areas that lack such spheres. The carbon-rich spheres may have been formed by biotic activity according to NASA scientists.[121][122][123] On 5 March 2011, Richard B. Hoover, a scientist with the Marshall Space Flight Center, speculated on the finding of alleged microfossils similar to cyanobacteria in CI1 carbonaceous meteorites.[124][125] However, NASA formally distanced itself from Hoover's claim.[126][127][128] According to American astrophysicist Neil deGrasse Tyson: "At the moment, life on Earth is the only known life in the Universe, but there are compelling arguments to suggest we are not alone."[129] Extreme environments on the Earth On 17 March 2013, researchers reported data that suggested microbial life forms thrive in the Mariana Trench, the deepest spot on the Earth.[130][131] Other researchers reported related studies that microbes thrive inside rocks up to 1900 feet below the sea floor under 8500 feet of ocean off the coast of the northwestern United States.[130][132] According to one of the researchers,"You can find microbes everywhere — they're extremely adaptable to conditions, and survive wherever they are."[130] Methane In 2004, the spectral signature of methane was detected in the Martian atmosphere by both Earth-based telescopes as well as by the Mars Express probe. Because of solar radiation and cosmic radiation, methane is predicted to disappear from the Martian atmosphere within several years, so the gas must be actively replenished in order to maintain the present concentration.[133][134] The Mars Science Laboratory rover will perform precision measurements of oxygen and carbon isotope ratios in carbon dioxide (CO2) and methane (CH4) in the atmosphere of Mars in order to distinguish between a geochemical and a biological origin.[135][136][137] Planetary systems It is possible that some planets, like the gas giant Jupiter in our solar system, may have moons with solid surfaces or liquid oceans that are more hospitable. Most of the planets so far discovered outside our solar system are hot gas giants thought to be inhospitable to life, so it is not yet known whether our solar system, with a warm, rocky, metal-rich inner planet such as Earth, is of an aberrant composition. Improved detection methods and increased observing time will undoubtedly discover more planetary systems, and possibly some more like ours. For example, NASA's Kepler Mission seeks to discover Earth-sized planets around other stars by measuring minute changes in the star's light curve as the planet passes between the star and the spacecraft. Progress in infrared astronomy and submillimeter astronomy has revealed the constituents of other star systems. Infrared searches have detected belts of dust and asteroids around distant stars, underpinning the formation of planets. Planetary habitability Main article: Planetary habitability Efforts to answer questions such as the abundance of potentially habitable planets in habitable zones and chemical precursors have had much success. Numerous extrasolar planets have been detected using the wobble method and transit method, showing that planets around other stars are more numerous than previously postulated. The first Earth-sized extrasolar planet to be discovered within its star's habitable zone is Gliese 581 c, which was found using radial velocity.[138] |
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