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Monday, November 07, 2005


Is there life on Mars?

Water vapor concentration on Mars. Image credit ESA.

The possibility of life on Mars has always fascinated us. There was Percival Lowell who interpreted Giovanni Schiaparelli's canalli to be water filled canals serving the Martian populace. The shifting dust patterns on Mars were interpreted as being due to seasonal changes in vegetation.

Then Mariner 4 flew past returning images of a battered frozen land. Barsoom was out.

But we still wondered about life on Mars. The Viking Landers had complicated instruments to look for life on Mars, and returned ambiguous results that are still being argued over.

Then came the Martian meteorite ALH84001, there were traces of organic chemicals, life-like isotope ratios and what looked intriguingly like microfossils. After lots of debate most researchers think that ALH shoes no clear signs of Martian life, but there is still ongoing debate.

Finally there was the excess of atmospheric methane. We have come a long way from Barsoom, but excess methane is an important clue. Methane is broken down very rapidly, and if there is substantial methane in Mars's atmosphere, it must be being produced. Methane can be produced in one of two ways 1) volcanism or 2) Living things (on Earth, burping cows are a major source of atmospheric methane). Not only does Mars have more methane than expected, but the methane is higher in certain regions, regions which correlate with water in the ground and above surface water vapor. This suggests that the methane is not from volcanic activity. There was also the suggestion that there was a lot of formaldehyde in Mar's' atmosphere, since formaldehyde was generated from methane, that implied that there was a lot more methane than could be accounted for by volcanism. However, the interpretation of the infrared spectrum is still open to doubt.

New data from the NASA infrared telescope facility also suggests that volcanism may not account for Mars's methane. They found no evidence of sulfur dioxide in the atmosphere, suggesting very low rates of volcanic outgassing which could not account for the levels of methane. Now, it is too early to declare Mars a wildlife reserve yet, and there are a number of possible non-volcanic geological systems which might produce methane, but at the very least it indicates that we should keep up the search for life on Mars. Bacterial flatulence may not be as exciting as Banth tracks, but it might just be the clue that will lead us to the first extraterrestrial life.

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