Life on Mars

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For the David Bowie song, see Life on Mars?. For the TV series, see Life on Mars (television).

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.

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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 features 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.

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Modern findings

Image:ALH84001 structures.jpg Image:History of water on Mars.jpeg

In recent years speculation has grown again, however – prodded by a study of the ALH84001 meteorite which concluded that it contained fossilized microbes. 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 extremophiles on Earth which survive under the harshest conditions. Some scientists have proposed a biological origin for the annual appearance and disappearance of dark dune spots near the polar regions of Mars.<ref name=fn1>Ganti, T. et al, "Evidence For Water by Mars Odyssey is Compatible with a Biogenic DDS-Formation Process". (PDF) Lunar and Planetary Science Conference XXXVI (2003)</ref><ref name=fn2>Horvath, A., et al, "Annual Change ofMartian DDS-Seepages". (PDF) Lunar and Planetary Science Conference XXXVI (2005).</ref>

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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, evidence for water currently under the surface of Mars was discovered in the form of flood-like gullies.<ref name=underground>Malin, Michael C., Edgett, Kenneth S., "Evidence for Recent Groundwater Seepage and Surface Runoff on Mars". Science (2000) Vol. 288. no. 5475, pp. 2330 - 2335.</ref> 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<ref name=moon>"University of Arizona Press Release" March 16, 2006.</ref>, 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 March 2004, NASA announced that its rover Opportunity had discovered evidence that Mars was, in the ancient past, a wet planet.<ref name=wet>Opportunity Rover Finds Strong Evidence Meridiani Planum Was Wet" - March 2, 2004, NASA Press release. URL accessed March 19, 2006.</ref> This has raised hopes that evidence of past life might be found on the planet today.

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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 March 2004, the orbiting ESA probe Mars Express confirmed the presence of methane in the martian atmosphere,<ref name=methane>"Mars Express confirms methane in the Martian atmosphere" March 30, 2004, ESA Press release. URL accessed March 19, 2006. </ref><ref name=methane2>Kerr, Richard A., "Life or Volcanic Belching on Mars?". Science news story. Vol. 303. no. 5666, p. 1953.</ref> which had earlier been suggested by observations of the UKIRT Infrared telescope on Hawaii and the Gemini South observatory in Chile in 2003.<ref name=methane3>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.</ref>

In February 2005, two NASA scientists reported that they had found strong evidence of present life on Mars, based in part on fluctuating methane signatures.<ref name=berger>"Exclusive: NASA Researchers Claim Evidence of Present Life on Mars". February 16, 2005, Space.com article. URL accessed March 19, 2006.</ref> The two scientists, Carol Stoker and Larry Lemke of NASA’s Ames Research Center, claimed that the methane signatures found in Mars' atmosphere resemble the methane production of some forms of primitive life on Earth, citing their own study of primitive life near the Rio Tinto river in Spain. NASA officials soon denied the scientists’ claims, and Stoker herself backed off from her initial assertions.<ref name=deny> "NASA: Researchers' Work May Influence Search for Mars Life, But No Evidence Yet". February 18, 2005, Space.com article. URL accessed March 19, 2006.</ref>

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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. So the claim was met with much skepticism.<ref name=form> "Formaldehyde claim inflames martian debate" - February 25, 2005, http://www.nature.com news story. URL accessed March 19, 2006.</ref> Now scientists generally agree that the claims were incorrect, probably due to a misinterpretation of the data from the PFS - which is currently out of operation, and appears to be broken permanently.<ref name=PFS>"Martian methane probe in trouble" - September 25, 2005 http://www.nature.com news story. URL accessed March 19, 2006.</ref>

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Ammonia on Mars

In the Martian atmosphere ammonia would be unstable and only last for a few hours. In fact a NASA scientist has said "There are no known ways for ammonia to be present in the Martian atmosphere that do not involve life".<ref name=ammonia>Ammonia on Mars could mean life. July 14, 2004, BBC news story. URL accessed March 19, 2006.</ref> 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.<ref name=ammonia2>"The search for life on Mars" July 27, 2004, http://www.nature.com news story. URL accessed March 19, 2006. </ref>

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See also

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References

<references/>

  • Wallace, Alfred Russel. Is Mars habitable? A critical examination of Professor Percival Lowell's book "Mars and its canals," with an alternative explanation, by Alfred Russel Wallace, F.R.S., etc. London, Macmillan and co., 1907.


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External links

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