The origin of methane in the atmosphere of Mars has been hotly debated for more than a decade, but a new discovery could finally provide an answer.
In 2004, the Mars Express orbiter detected faint traces of methane in the Martian atmosphere, not long after it arrived. Its discovery prompted a flurry of activity among astrobiologists who debated whether it was an ancient fingerprint of living organisms that once used to live there, or just an anomaly.
In the years that followed, this debate only intensified as the Curiosity rover announced the detection of a strong methane signal on 15 June 2013. Now, for the first time, this discovery by the Mars rover has been backed by an independent investigation into old data captured by the Planetary Fourier Spectrometer on board the Mars Express the very next day.
This uncovering of the data, using a new observation technique, helped the Italian and Belgian scientists pinpoint the potential origin of the methane and explain what has led to a series of spikes over the past number of years. This allowed them to collect several hundred measurements over a short period of time.
“In general we did not detect any methane, aside from one definite detection of about 15 parts per billion by volume of methane in the atmosphere, which turned out to be a day after Curiosity reported a spike of about six parts per billion,” said Marco Giuranna from the Institute for Space Astrophysics and Planetology in Rome and lead author of the new paper published to Nature Geoscience.
“Although parts per billion in general means a relatively small amount, it is quite remarkable for Mars – our measurement corresponds to an average of about 46 tonnes of methane … present in the area of 49,000 sq km observed from our orbit.”
Seeping out from ice
When Curiosity detected methane almost six years ago, it was speculated that the gas originated north of the rover because the prevailing winds were southward, and that the release likely occurred inside the crater. These new findings dismiss this theory based on the new geological evidence.
After conducting two independent analyses to pinpoint the methane’s origin, the team concluded the likeliest scenario: that it seeped out from frozen ice below the surface.
The paper’s co-author, Giuseppe Etiope, explained: “We identified tectonic faults that might extend below a region proposed to contain shallow ice. Since permafrost is an excellent seal for methane, it is possible that the ice here could trap subsurface methane and release it episodically along the faults that break through this ice.
“Remarkably, we saw that the atmospheric simulation and geological assessment, performed independently of each other, suggested the same region of provenance of the methane.”
The researchers now hope to better understand how methane is removed from the atmosphere.