Martian methane shows that life is unlikely

Mars - a dead planet?

With the talk of new missions to Mars, including manned flights within the next generation, it’s worth looking at what we know about our neighbouring planet’s environment, and whether it supports life today, or did in the distant past.

In tomorrow’s edition of Nature there is a paper by two scientists at the Laboratoire de Météorologie Dynamique in Paris who report on observations and results from a computer model which show that methane is unevenly distributed in the Martian atmosphere, and that the rapid production and loss of the greenhouse gas cannot be understood in terms of our current knowledge of the planet’s atmospheric chemistry.

Based on the known chemistry, methane should have an atmospheric lifetime of several centuries. However, Franck Lefèvre and François Forget show that on Mars there appears to be a loss process some 600 times faster than that predicted by photochemistry alone.

If Lefèvre and Forget’s model is correct, then, in order to explain the observations, the destruction of methane on the planet’s surface must occur within an hour or so. That almost certainly rules out biology, in which case the likely cause is geological processes which result in an extraordinarily harsh environment for the survival of organic compounds in the surface layer.

The authors conclude:

“Such a [methane] lifetime suggests that organics are quite readily scavenged from the modern Martian environment, if reactions in the surface are the only cause of the observed methane variations. This would leave little hope that life as we know it can exist at present or that evidence of past life can be preserved in the shallow surface layer.”

That is a very strong statement, and one that would seem justified given the observational data and model outputs on methane in the Martian atmosphere. As the authors go on to say, future missions will allow the hypothesis to be tested, and we should know for sure within the next 10 years whether life exists today on Mars, or once existed on the planet’s surface.

But I wouldn’t hold your breath! Everything we currently know about Mars points to it being a planet totally devoid of life. As James Lovelock of Gaia fame showed back in the 1970s, the atmosphere of Mars exists in a state close to chemical equilibrium, with an overwhelming abundance of carbon dioxide. Lovelock declared that Mars is most likely dead, and the latest data support this decades-old interpretation. If life once flourished on Mars, all traces of it would appear to have since been obliterated in what is a most hostile environment.

Further reading

Franck Lefèvre & François Forget, “Observed variations of methane on Mars unexplained by known atmospheric chemistry and physics”, Nature 460, 720 (2009)