Mars drier than thought, but glass still half full
An ancient Mars of rolling oceans is an image pregnant with implications and one that has gained a lot of currency amongst researchers in recent years, but it is good to be occasionally reminded that this is just a theory, and there are plenty of other ways of interpreting the evidence. New Scientist magazine is reporting this week that results from Mars Express cast some doubt on the idea that Mars was once a very wet environment, because it appears to have lacked the necessary carbon-dioxide-rich atmosphere to make this possible. Since the sunlight reaching Mars is 25% less than that on Earth, a very effective greenhouse effect powered by large concentrations of CO2 would have been needed to generate a warm thick atmosphere, 80% more than is experienced on Earth. Analysis of clays, or phyllosilicates, found on the planet by the OMEGA spectrometer on Mars Express seems to indicate that the presence of these clays rules out a large amount of CO2 in the atmosphere since this would have prohibited their formation. Methane, which can also act as a greenhouse gas has been proposed as an alternative driver of a greenhouse effect, but Methane in any significant volume would need an extremely active biosphere, and while it is nice to imagination a tropical Mars in the past, this does not seem very likely. Intriguingly, another alternative has it that large meteor impacts may have caused very brief flurries of wet activity on Mars, in the order of a few thousand years at a time. The question then arises, would a few thousand years of rain (even repeated multiple times) have been sufficient to carve out the river valley like features seen on Mars. Read the article at New Scientist.