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Scientists have long speculated about the possibility of life on Mars due to that planet's proximity and similarity to Earth . It remains an open question whether life exists on Mars now, or existed there in the past. HISTORY It has long been speculated that there may be life on Mars, due to the many similarities the planet has with Earth . Mars' Polar Ice-caps were observed as early as the mid-17th century, and they were first proven to grow and shrink alternately, in the summer and winter of each hemisphere, by William Herschel in the latter part of the 18th century. By the mid-19th century, astronomers knew that Mars had certain other similarities to Earth, for example that the Length Of A Day On Mars was almost the same as a day on Earth. They also knew that its Axial Tilt was similar to Earth's, which meant it experienced seasons just as Earth does - but of nearly double the length owing to its Much Longer Year . These observations led to the increase in speculation that the darker Albedo Feature s were water, and brighter ones were land. It was therefore natural to suppose that Mars may be inhabited by some for of life. Speculation about life on Mars exploded in the late 19th century, following telescopic observation of apparent Canals — which were later found to be optical illusions. In 1854 , William Whewell , a fellow of Trinity College , Cambridge University who popularized the word ''scientist,'' theorized that Mars had seas, land and possibly life forms. In 1895 , American astronomer Percival Lowell published his book ''Mars,'' followed by ''Mars and its Canals'' in 1906 , proposing that the canals were the work of a long-gone civilization. This idea led British writer H. G. Wells to write '' The War Of The Worlds '' in 1897 , telling of an invasion by aliens from Mars who were fleeing the planet’s desiccation. Better telescope imagery, and especially the photos taken by the Mariner 4 probe in 1965 showed an arid Mars without rivers, oceans or any signs of life. Intense UV Radiation made the planet extremely hostile to life as we know it. Officially the Viking lander's tests for microbes in 1976 were inconclusive, but most scientists hold that their findings can be explained on the basis of chemical reactions alone. Observations made in the late 1990's by the Mars Global Surveyor confirmed the suspicion that Mars, unlike Earth, no longer possessed a substantial Global Magnetic Field , thus allowing potentially life-threatening Cosmic Radiation to reach the planet's surface. Scientists also speculate that the lack of shielding due to Mars' diminished global magnetic field helped the Solar Wind blow away much of Mars' Atmosphere over the course of several billion years. MODERN FINDINGS In recent years speculation has grown again, however – prodded by a study of the ALH84001 Meteorite which concluded that it contained Fossil ized Microbe s. Other scientists have subsequently sought to explain these findings on the basis of chemical processes. Both remain highly controversial within the scientific community. Another glimmer of hope for past and present life on Mars has been revealed with the ongoing research into ) Lunar and Planetary Science Conference XXXVI (2005). Water on Mars No Mars probe since Viking has tested the Martian soil directly for signs of life. NASA's recent missions have focused on another question: whether Mars held lakes or oceans of liquid water on its surface in the ancient past. Many scientists have long held this to be almost self-evident based on various geological landforms on the planet, but others have proposed different explanations -- wind erosion, carbon dioxide oceans, etc. Thus, the mission of the Mars Exploration Rovers of 2004 was not to look for present or past life, but for evidence of liquid water on the surface of Mars in the planet's ancient past. In June (2000) Vol. 288. no. 5475, pp. 2330 - 2335. Deep subsurface Water deposits near the planet's liquid core might form a present-day habitat for life. However, in March 2006 , astronomers announced the discovery of similar gullies on the Moon "University of Arizona Press Release" March 16, 2006., which is believed to have never had liquid water on its surface. The astronomers suggest that the gullies could be the result of micrometeorite impacts. In Press release. URL accessed March 19, 2006. This has raised hopes that evidence of past life might be found on the planet today. Methane on Mars As Methane cannot persist in the Martian Atmosphere for more than a few hundred years, existence of it suggests that either Mars has recently been Volcanically active, or that some kind of Extremophile life form similar to some present on Earth is Metabolising Carbon Dioxide and Hydrogen and producing methane. In news story. Vol. 303. no. 5666, p. 1953. which had earlier been suggested by observations of the UKIRT Infrared Telescope on Hawaii and the Gemini South observatory in Chile in 2003.Mumma, M. J.; Novak, R. E.; DiSanti, M. A.; Bonev, B. P., "A Sensitive Search for Methane on Mars" (abstract only). American Astronomical Society, DPS meeting #35, #14.18. In article. URL accessed March 19, 2006. Formaldehyde on Mars Since Formaldehyde is produced in the Oxidation of Methane , which occurs on Mars, it is unsurprising that it is detected in the Martian atmosphere. But in February 2005, it was announced that Planetary Fourier Spectrometer (PFS) on the European Space Agency 's Mars Express Orbiter detected substantially more formaldehyde than anyone had reasonably expected, strongly pointing to other explanations such as microbial life. This claim was widely debated in the scientific community. "Formaldehyde claim inflames martian debate" - February 25, 2005, http://www.nature.com news story. URL accessed March 19, 2006.Scientists sceptical to the measurements say that the data from the PFS has been misinterpreted. "Martian methane probe in trouble" - September 25, 2005 http://www.nature.com news story. URL accessed March 19, 2006. Ammonia on Mars In the Martian atmosphere news story. URL accessed March 19, 2006. For this reason, the detection of ammonia would be extremely important for the debate of whether there is life on Mars. In July 2004 rumours began to circulate that Vittorio Formisano, the scientist in charge of the Planetary Fourier Spectrometer (PFS), would announce their discovery of ammonia at an upcoming conference. It later came to light that none had been found; in fact some noted that the PFS was not precise enough to distinguish ammonia from Carbon Dioxide anyway. "The search for life on Mars" July 27, 2004, http://www.nature.com news story. URL accessed March 19, 2006. SEE ALSO
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