IF YOU鈥橰E holding out hope for life on Mars, there鈥檚 some good news and some bad news. A study of indigenous rocks here on Earth suggests that microbes would have a plentiful supply of energy on the Red Planet. But a report on tantalising traces of Martian plant life has bitten the dust.
The hope for the presence of life on Mars lies below the surface, where many scientists believe there is still water in liquid form. On Earth, some microbes that live deep within rocks get their energy from hydrogen, which can be produced when water reacts with iron in the rocks.
But Friedmann Freund of NASA Ames Research Center in Moffett Field, California, says the sporadic nature of this hydrogen production deep underground has always bothered him, since it takes place only on freshly fractured surfaces. 鈥淐ommunities [of microbes] could not last for millions of years if they had to depend on such a fickle hydrogen supply,鈥� he says.
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But Freund has found a way for hydrogen to form in the absence of water and cracking rocks. As rocks far beneath the Earth鈥檚 crust cool, he says, hydroxyl ions that contaminate the rock crystal break off and form hydrogen gas that gets trapped within the rock. He has already shown that the reaction is possible. Now his team has crushed a variety of rocks that don鈥檛 contain water, such as granite, and found that they do release hydrogen gas. 鈥淭hat means microbes on Mars would have an almost inexhaustible supply of energy,鈥� he says.
鈥淚t鈥檚 interesting to see all the ways the subsurface can generate hydrogen gas,鈥� says Todd Stevens of Portland State University in Oregon, who studies hydrogen-eating bacteria. But he questions whether this process alone would leak enough gas to power the bugs.
Freund thinks the gas supply would be both reliable and sufficient. In one experiment, his team found that a rock sample continued to release a steady supply of gas for over a week. And he points out that as microbes digested the gas, more of it would be drawn out. 鈥淚t鈥檚 like having a bank send you a cheque every day,鈥� he says. 鈥淚t would be a small cheque, but it would still be a good living wage.鈥�
Recently prospects for plant life seemed upbeat too, according to Carol Stoker, also at NASA Ames. Her team analysed images from the Superpan, a camera mounted on the Mars Pathfinder lander, for traces of chlorophyll, the pigment in plants that captures energy from sunlight. Although another team previously found no sign of chlorophyll (快猫短视频, 3 January 1998, p 68), Stoker reports in an abstract submitted to this week鈥檚 Astrobiology Science Conference at NASA Ames that 鈥渢wo intriguing cases occur in small areas on the ground near the spacecraft.鈥�
But a NASA spokeswoman says analysis carried out since the abstract was submitted has convinced Stoker that the spots are not evidence of Martian photosynthesis but a computer glitch. For the time being at least, final proof of past or present Martian life continues to elude us.