The mystery of the vanishing Martian methane

The 2004 discovery of methane means that either there is life on Mars, or that volcanic activity continues to generate heat below the martian surface. Now, the ESA plans to find out which it is.

Methane mystery. Something is removing Martian methane

Either outcome is big news for a planet once thought to be biologically and geologically inactive. The methane mystery started soon after December 2003, when ESA’s Mars Express arrived in orbit around the red planet. As the Planetary Fourier Spectrometer (PFS) began taking data, the instrument team saw a puzzling signal - as well as the atmospheric gases they were anticipating, such as carbon monoxide and water vapour, they also saw methane.

Methane is thought to be stable in the martian atmosphere for around 300 years, however, the methane had almost entirely vanished by early 2006. Clearly something unusual is going on at Mars. “We thought we understood how methane behaved on Mars but if the measurements are correct then we must be missing something big,” said Franck Lefèvre, Université Pierre et Marie Curie in Paris and a member of Mars Express’s SPICAM instrument team.

Together with his colleague François Forget, Lefèvre has investigated the disappearance using a computer model of Mars’ climate. “We have tackled the problem as atmospheric physicists, without worrying about the nature of the source of the methane,” he says.

They found that, while their computer model can reproduce atmospheric species such as carbon monoxide and ozone, it is unable to reproduce the behaviour of the methane. “Something is removing the methane from the atmosphere 600 times faster than the models can account for,” says Lefèvre. “Consequently, the source must be 600 times more intense than originally assumed, which is considerable even by Earth’s geological standards.”
To help get to the bottom of the methane mystery, ESA and the Italian space agency (ASI) are to hold a three-day international workshop in November. The assembled scientists will discuss the results and plan strategies for the future study of methane.

In July, ESA agreed with NASA to launch joint missions to Mars. The topic of methane is of such importance that it will be most likely addressed in these future missions. “Understanding the methane on Mars is one of our top priorities,” says Witasse.