A taste for Martian living


By Andy Coghlan in Chicago SPECULATION that Mars can support life has intensified following experiments which show that bacteria can grow in conditions designed to mimic those beneath the surface of the Red Planet. Researchers at the University of Arkansas in Fayetteville have grown bacteria on ash from a Hawaiian volcano, the closest earthly equivalent to Martian soil. Over the past few years, biologists have discovered bacteria thriving several kilometres below the Earth’s surface (“The intraterrestrials”, New Scientist, 7 March 1998, p 28). The methanogen bacteria studied by Timothy Kral and his colleague Curtis Bekkum survive by combining hydrogen and carbon dioxide, releasing energy and producing methane as a waste product. They can scavenge nutrients from the most barren soils and rocks. Kral and Bekkum grew four species of methanogens in the volcanic soil, which was exposed to a three-to-one mixture of H2 and CO2 to simulate what they think conditions must be like up to 3 kilometres beneath the Martian surface. All the bacteria survived, even when each gram of soil contained only 0.1 millilitres of water. “Methanobacterium barkeri survived best for the least amount of water,” says Bekkum. Kral hopes that the results will silence sceptics who argue that there are not enough nutrients and carbon available on Mars to support life. “It’s an interesting start,” agrees John Parkes of the University of Bristol, who studies terrestrial subterranean bacteria. But he notes that the researchers first grew their bacteria on media lacking organic carbon, which would have primed them to survive in barren soil. Next, the Arkansas researchers want to find out if the methanogens can survive in conditions that mimic those near to the Martian surface. The Viking and Pathfinder probes suggested that the surface atmosphere is 95 per cent CO2, 3 per cent nitrogen, 1.9 per cent argon and 0.1 per cent carbon monoxide. Kral and Bekkum will release this mix of gases into a chamber mimicking the Red Planet’s atmospheric pressure—one hundredth of Earth’s—and bombard the methanogens with radiation to simulate the effects of the cosmic rays and ultraviolet light that strike the Martian surface. “Maybe NASA will allow us to grind Martian meteorites to create a real Martian soil,” says Bekkum. If the bacteria survive in this hostile environment, it will boost hopes of finding life on Mars—and suggest that it might even be possible to “terraform” the Red Planet by seeding it with methanogens to make it suitable for colonisation. Methane released by the bacteria would create a greenhouse effect, warming the planet and releasing its frozen water. But Kral stresses that he isn’t advocating such grandiose plans. “It’s very controversial,” he says. More on these topics:
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