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Esa / ATG medialab
Illustration: Mars Express operates in orbit around the red planet since 2003
A European spacecraft has confirmed a report that methane would be released from the surface of Mars.
The methane peak was first measured by the NASA Curiosity robot at the surface; now this has been confirmed by the Mars Express orbiter.
The nature and extent of methane in the Martian atmosphere are intensely debated.
Gas is of interest because terrestrial methane can come from life forms as well as geological processes.
Methane is supposed to have only a very short life in the Martian atmosphere; its detection means that it must have been rejected very recently.
A strong methane signal was measured by the Curiosity mobile on June 15, 2013.
The measurement was confirmed by data collected the next day by the Fourier Planetary Spectrometer (PFS) aboard Mars Express.
The results of two studies are described in Nature Geoscience.
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"In general, we did not detect any methane, apart from a definitive detection of approximately 15 parts per billion of methane volume in the atmosphere, a day after Curiosity reported a rise about six parts per billion, "said Marco Giuranna, senior investigator for the PFS.
"Although the parts per billion are generally a relatively small amount, this is quite remarkable for Mars." Our measurement is an average of about 46 metric tons of methane present in an area of 49,000 square kilometers observed since our orbit. "
At the time of the detection of Curiosity, it was thought that the methane could have come from the north of the rover (because the prevailing winds were facing south) and that the release came from inside the crater Gale, the place of 39, Curiosity landing.
The team conducted two independent analyzes to target potential source areas of methane, dividing a large area around the crater of Gale into grids of approximately 250 square kilometers.
Biology or geology?
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NASA
Peak methane reported for the first time by Curiosity rover in 2013
Methane can be produced in different ways on Mars.
If microbes still exist, they are a possible source. The methane produced by microorganisms in the distant past could also be trapped in the ice. When the ice melts, it could then release the old methane into the atmosphere.
However, some geological processes can produce methane and do not require biology. These include serpentinization – a process of mineral alteration of the crust involving heat and water. Methane can be manufactured downstream of serpentinization.
Marco Giuranna suspects that the plume does not come from Gale Crater.
Scientists have examined the area around Gale for features that could lead to gas infiltration.
This process is well known on Earth to occur along tectonic faults and natural gas fields.
"We have identified tectonic faults that could extend below a proposed area to contain shallow ice.As permafrost is an excellent seal for methane, it is possible that the ice would trap methane beneath the surface and release it episodically along the faults that cross it, "said Giuseppe Etiope of the National Institute of Geophysics and Volcanology in Rome, co-author of one of the studies.
"Remarkably, we have seen that atmospheric simulation and geological evaluation, performed independently of one another, suggested the same source region of methane."
The Orbiter ExoMars Trace Gas Orbiter, designed to make a detailed inventory of the Martian atmosphere, was launched in 2016. However, it has not yet reported on its scientific results.
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