[The following is an excerpt from a paper I wrote on Mars and the speculation as to whether life could exist on Mars. This was in 2007, but hopefully still applicable.]
Questions and theories to the origin of life inevitably cause one to muse, regardless of your belief system, on what rare circumstances may belong to this planet. The race to space, though undoubtedly driven by economic and ideal motives, in the end, was an expression of an even deeper curiosity: is life on earth indeed the jewel of the cosmos? Until relatively recent, it was not uncommon for individuals to imagine that life could exist in abundance on various planets within our own solar system, especially on Mars. H. G. Wells simply transcribed into popular tale what was broadly conceived as possible by the late 19th century – that Mars contained intelligent life. In 1950 Ray Bradbury published the Martian Chronicles, imagining a Mars that had, in the distant past, teemed with life far more advanced and civilized than earth. Even as late as 1976 Carl Sagan boasted that the question to be answered by the Viking landers was not if they would find life, but what type.(1)
But the progress of technology has since sobered these imaginations. For the cold, calculating eyes of satellite, lander, and probe have shown us that the surface of Mars, and all the planets which they have scoped, are bereft of signs of life. Nonetheless, the march of science has continued, and advances in biology and chemistry have increased our understanding of the building blocks of life, life’s flexibility, and that some extreme environments once thought to be completely hostile, are able to support life. Consequently, hope that life may yet be found has endured, even if this hope has been demoted from one time intelligent life to crawling creatures to now simply microbes identifiable only with instrumentation. This enduring hope is the prime motivator behind NASA’s ongoing commitment to the race for life on our red neighbor.
Questions concerning the planet’s relationship with water are numerous to be sure–primarily because all known types of life on earth share a universal trait: dependence on water.
So where are we in our trek to finding water on Mars? The evidence is fairly convincing that water once covered much of the Martian surface. Villis Marineris is a well-known canyon system that many believe was at one time filled with water. The amount is staggering: it would cover the entire Amazon basin.(1) That much water would be more than enough to give life a starting chance. But what about the length of time? In some regions there are indications that fluids sat for a very long time. Scientists draw these conclusions from the chemical reactions apparent in rock formations.(7) Whether or not these fluids were largely composed of water, is still to be confirmed.
The evidence for water only begins there. In 2004 the Mars rovers Opportunity and Spirit landed on opposite ends of the globe and each began their dutiful search for indications of water. Opportunity, the more fortunate of the two, landed in a shallow crater of exposed bedrock. “We got lucky,” said Steve Squyres of Cornell University, “Tiger Woods couldn’t do this. We went right into it…the beauty of it is that the crater walls expose materials that we wouldn’t otherwise see.”(8) He was referring to the fine layers they observed running through the rock, suggesting the possibility that the exposure was sedimentary rock, formed on the floor of an ancient sea. After examining the rock, Opportunity found that it was as much as 40% sulfate salts, indicating that salt water had at one time covered the area and after evaporation, left salt components behind. The long arm of NASA had reached across the 35 million mile span and tested the soil for evidence of water, and the test proved positive.
Two years later more evidence for water appeared, only this time the evidence suggested that water might currently be on the planet, running underground. The Mars Global Surveyor (MGS), before it went silent about two years ago, had captured photos of the planet’s surface for seven years. Naturally, given the amount of time, many of these areas were retakes. When comparing the ‘before’ and ‘after’ photos, some experts believe that the evidence of flowing water is very high. The following photographs illustrate this:
http://nssdc.gsfc.nasa.gov/planetary/image/noachis_gullies.jpg
http://www.crystalinks.com/marswater1206.jpg
The theory is that some water seeps up through cracks and gets frozen just behind the surface for some time. The pressure builds and eventually the water bursts out through the surface. Some estimate from the photos taken that the amount of bursting water ranges from five to ten Olympic size swimming pools. It then runs in streaks over the sand and, quickly evaporating, often leaves behind it white trails of either salt or frost.(9)
[I apologize that I haven't added the sources. They're saved on another file and will do so soon.]
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