Life on Mars

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For other uses, see Life on Mars (disambiguation).

Scientists have long speculated about the possibility of life on Mars owing to the planet's proximity and similarity to Earth. It remains an open question whether life exists on Mars now, or existed there in the past.

Contents 1 History 2 Modern findings 2.1 Water on Mars 2.2 Methane on Mars 2.3 Formaldehyde on Mars 2.4 Ammonia on Mars 3 See also 4 References 5 External links

[edit] History

Mars's 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 form 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, 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 landers' biological experiments 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's diminished global magnetic field helped the solar wind blow away much of Mars's atmosphere over the course of several billion years.

[edit] Modern findings

In recent years speculation has grown again, however—prodded by a study of the ALH84001 Mars meteorite which concluded that it contained fossilized microbes. This explanation was disproved, however, and it was discovered that the worm-like appearance of the fossils was due to the coating of gold on the samples for viewing under a microscope (without the gold it appeared very rough, square, and generally more rock-like). Other scientists have subsequently sought to explain these findings on the basis of chemical processes. Both remain highly controversial within the scientific community. Other Mars meteorites such as the Nakhla meteorite were suggested to have evidence of life also.

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.^[1][2]

[edit] 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.^[3] 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,^[4] 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.^[5] This had raised hopes that evidence of past life might be found on the planet today.

In December 2006, NASA showed images taken by the Mars Global Surveyor that suggested that water occasionally flows on the surface of Mars. The images did not actually show flowing water. Rather, they showed changes in craters and sediment deposits, providing the strongest evidence yet that water coursed through them as recently as several years ago, and is perhaps doing so even now. Some researchers were skeptical that liquid water was responsible for the surface feature changes seen by the spacecraft. They said other materials such as sand or dust can flow like a liquid and produce similar results. The findings are to be published in the December 8, 2006 issue of the journal Science.^[6]

[edit] Methane on Mars

As methane cannot persist in the Martian atmosphere for more than a few hundred years, its presence suggests either that it is being replenished by some unidentified volcanic or geologic process, or that some kind of extremophile life form similar to some existing on Earth is metabolising carbon dioxide and hydrogen and producing methane.

In March 2004, the orbiting ESA probe Mars Express reported detecting methane in the Martian atmosphere,^[7][8][9] which had earlier been suggested by observations of the United Kingdom Infrared Telescope on Hawaii and the Gemini South observatory in Chile in 2003.^[10]

Others have proposed that the a process called serpentinization, wherein the mineral olivine is converted into serpentine in the presence of liquid water, may be occurring somewhere in the subsurface of Mars and releasing enough methane to explain the observations.^[11]

[edit] Formaldehyde on Mars

In February 2005, it was announced that the 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 continues to be widely debated in the scientific community.^[12]Scientists skeptical to the measurements say that the data from the PFS has been misinterpreted.^[13]

[edit] 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".^[14] 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.^[15]

[edit] See also

• Planetary habitability
• Face on Mars
• Mars civilization theory
• Astronomy on Mars
• List of artificial objects on Mars
• Martian
• Terraforming

[edit] References

[edit] External links

• Study Reveals Young Mars Was A Wet World
• NASA - The Mars Exploration Program
• Arthur C. Clarke sees life on Mars
• Scientists have discovered that Mars once had saltwater oceans
• BBC News: Methane on Mars could signal life
• BBC News: Ammonia on Mars could mean life
• Scientists say that life on Mars is likely today
• Ancient salty sea on Mars wins as the most important scientific achievement of 2004 - Journal Science
• Mars meteor found on Earth provides evidence that suggests microbial life once existed on Mars
• Scientific American Magazine (November 2005 Issue) Did Life Come from Another World?
• Audio interview about "Dark Dune Spots"