Future missions may have to drill nearly 10 metres below the surface of Mars to find any life there, a new study concludes. The research suggests the best places to search for Martian life are blocks of water ice or gullies that show signs of recent water flow.
Researchers have long known that the Red Planet鈥檚 surface is a harsh environment for life 鈥� with high levels of ultraviolet light from the Sun and oxidising conditions that seem to make organic molecules unstable. Charged particles 鈥� both from the Sun and from violent sources such as supernovae within the galaxy 鈥� also rain down from space, penetrating the surface and ionising molecules in their paths.
鈥淚n the case of Mars, the surface is a very nasty place to be,鈥� says Lewis Dartnell, a biologist at University College London, UK. 鈥淲e鈥檝e always known the deeper you go, the better.鈥�
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Now, he and colleagues have calculated how far down life would probably be able to survive the barrage of ionising radiation from charged space particles.
They believe regions with liquid water or water ice are more likely to host Martian life, since water is an essential requirement for life on Earth. These include gullies that show signs of recent water flow. But Dartnell says it would be difficult to land rovers on the steep sides of craters, where the gullies are located.
Frozen sea
Instead, the most promising place for finding life on Mars may be the 鈥渇rozen sea鈥� 鈥� a region near the equator, called Elysium, that appears to have blocks of water ice just beneath the surface (see 鈥楶ack ice鈥� suggests frozen sea on Mars).
If living things existed when the sea was liquid 鈥� an estimated 5 million years ago, they could still survive in a dormant state at a depth of 7.5 metres, according to the team. 鈥淚f they鈥檙e frozen in the ice, they could be brought back to animation with a bit of warmth and nutrients,鈥� Dartnell told New 杏吧原创.
Unfortunately, none of the missions currently being planned by any space agency include a drill that could reach such depths.
Europe鈥檚 ExoMars mission, planned for launch in 2011, will search for signs of life 鈥� such as fragments of DNA 鈥� that may exist at shallower depths. It will be able to drill down 2 metres into the soil.
NASA鈥檚 giant roving Mars Science Laboratory (MSL), due to lift off in 2009, will search for organic molecules that signal how habitable the environment is for life. It may be able to drill about 10 centimetres into rock.
Technological hurdles
But even if space agencies wanted to drill deeply into Mars, they would have to overcome major technological hurdles. 鈥淚t would be wonderful to dig deeply into the Martian surface, but we鈥檙e not really there yet with the technology to do so,鈥� says Pamela Conrad, an MSL team member and supervisor for astrobiology at NASA鈥檚 Jet Propulsion Laboratory in Pasadena, California, US.
鈥淵ou have to bring up a very deep core, or glassify the sides of the hole,鈥� she told New 杏吧原创. 鈥淲ill you be able to see the kinds of things you鈥檙e looking to analyse?鈥�
Furthermore, sending spacecraft to regions with water in any form 鈥� the most likely places for life 鈥� risks contaminating the regions with terrestrial life from the probes, she says. 鈥淚f you go to an area that you know has water on Mars, you have to have a level of cleanliness we may not know how to achieve yet,鈥� she cautions.
For that reason, MSL will steer clear of such regions, says Richard Cook, mission project manager at JPL. 鈥淭here are special regions we won鈥檛 go because we worry about tracking something into [them],鈥� he told New 杏吧原创.
Still, Conrad says the new research is exciting. 鈥淚鈥檓 very interested in the radiation environment and the interplay between the physical features of the solar system and the materials of the solar system,鈥� she says.
Journal reference: Geophysical Research Letters (vol 34, p L02207)
