The fascination with Mars and its habitability has been going on for centuries. And indeed, Mars holds the greatest life potential of all the other planets, since water seems to have been flowing on its surface in the past. The flyby of Mariner 4 in July 1965 has forever changed the hopes that Mars was inhabited by intelligent beings. Mariner 4 revealed a dry planet with a small mass, while the Viking landers confirmed that there was no sign of life on Mars’ surface. [1] The Martian landscape revealed by probes is a witness of a geological active past. On Earth, plate tectonics was essential in promoting biodiversity and defense against mass extinctions. A geological active Red Planet could have been a good habitat for life. In the same time, the Mars Reconnaissance Orbiter has revealed the possibility that salty water could flow on the surface during the Martian summer. Frozen water has been detected in middle to high-latitude regions of the planet. [2]
The Martian surface seems lifeless, static, inhospitable, cold, dry, and desolate. Mars is about half the size of Earth and has lower gravity and pressure. Temperature goes down to 100°C bellow zero every night, and the atmosphere has no oxygen, but it is composed almost entirely of carbon dioxide. Liquid water would freeze and evaporate in the same time on the surface. The Red Planet has lost its magnetic field and atmosphere, and the liquid water disappeared from the surface. Huge dust storms darken its sky for weeks or months. [3] If life has survived here, it must be hidden below the surface where water may still be liquid.
A recent discovery has revealed that Mars’ atmosphere contains light traces of methane. Methane is abundant on Earth, and 90 to 95 percent of it has biological sources. [4] Since ultraviolet radiation on Mars would destroy the methane, the gas must have been recently produced. Geological activity could also be a source, but methane was discovered in areas where there are no volcanoes. The presence of this gas in Mars’ atmosphere could originate from microorganisms living beneath the surface. [5] However, hard proof evidence may only be available when humans will reach Mars. Until then, scientists rely on the rovers Spirit and Opportunity to discover any traces of life on the neighboring planet. While Spirit has been silent since March 2010, Opportunity is still active. The Mars Science Laboratory, nicknamed Curiosity, launching in November 2011 and scheduled to land in August 2012, has as main mission to search for past and present biological activity.
Notes:
[1] Jones, Barrie William. The Search for Life Continued. Chichester : Praxis Publishing, 2008, 78.
2 Webster, Guy, Cole, Steve, Stolte, Daniel. NASA Spacecraft Data Suggest Water Flowing on Mars. NASA, Aug.4, 2011. http://www.nasa.gov/mission_pages/MRO/news/mro20110804.html (accessed October 11, 2011), 1.
3 Webster, Guy, Cole, Steve, Stolte, Daniel. NASA Spacecraft Data Suggest Water Flowing on Mars. NASA, Aug.4, 2011. http://www.nasa.gov/mission_pages/MRO/news/mro20110804.html (accessed October 11, 2011), 79.
4 Atreya, Sushil K. "The Mystery of Methane on Mars & Titan. (Cover story)." Scientific American 296, no. 5 (May 2007): 42-51. Academic Search Premier, EBSCOhost (accessed October 11, 2011), 42.
5 Seeds, Michael. The Solar System. Boston
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