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If you're not a chemist, an astrobiologist or a scientist, and that includes most of us, then a tiny smell of methane, almost imperceptible, in the Martian atmosphere can seem very serious. But that's the case, nice humans. It is.
Why?
Because this could be a sign that a life process is at work. And even we, non-scientists, have asked ourselves at one point whether the only life in the solar system, or perhaps in the whole universe, is confined here on Earth.
Let's go inside.
Some time ago, in 2013 and 2014 to be exact, NASA's MSL Curiosity mobile detected methane peaks in the atmosphere at Gale Crater. And much earlier, in 2004, the Mars Express Orbiter (MEO) also detected methane in the Martian atmosphere. Methane is important because it could be an indicator of a living process. (Methane can also be produced by non-biological processes.)
Methane does not stay long. Once released into the atmosphere, it can be quickly destroyed by natural atmospheric processes. So any methane detected in the Mars atmosphere means that it must have been released recently, although it could have been produced millions of years ago, even billions of years ago, and stuck in underground rock formations .
On Earth, most of the methane is produced by living creatures; microorganisms in the sedimentary layers or in the intestines of ruminants, for example. Part of it is produced by abiotic or non-living processes, but finding methane on Mars remains, at least potentially, a big problem.
Now, the European Space Agency, which operates the Mars Express orbiter, examined the data from June 15, 2013, when Curiosity detected a spike in methane and found something. The Fourier Planetary Spectrometer (PFS) aboard the MEO detected methane at the same location as Curiosity a day later.
This is the first time that a Curiosity methane spike is saved by other independent observations. These results are presented in a new article published on April 1 in Nature Geoscience.
The results of MEO are part of a new method of analyzing data from his spectrometer. The technique involves collecting several hundred measurements over an area over a short period of time. The team at the origin of the results has also developed a new way to analyze the data.
"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 peak of About six parts per billion.", Says Marco Giuranna of the National Institute of Astrophysics – Institute of Space Astronomy and Space Planetology in Rome (Italy), principal investigator of the PFS experiment and lead author of the. article reporting the results Nature Geoscience.
15 parts per billion is not a huge amount. But this remains significant.
"Although the parts per billion are generally a relatively small amount, this is quite remarkable for Mars – our measure is an average of about 46 tonnes of methane present in an area of 49,000 square kilometers observed since our orbit., "Said Giuranna in a press release.
Another correlation supports this confirmation. Ten other observations made by the Mars Express orbiter spectrometer showed no methane, which corresponds to a period of time when Curiosity also exhibited weak measurements.
So where does it come from? Initially, the prevailing wind at the Curiosity site at Gale Crater came from the north. Scientists thought that the methane came from inside the crater itself, transported to Curiosity by the wind. It does not seem so likely.
"Our new Mars Express data, taken one day after the Curiosity registration, modifies the interpretation of the origin of methane, particularly when considering global atmospheric circulation patterns as well as local geology."Giuranna said. "Based on geological evidence and the amount of methane we measured, we believe that it is unlikely that the source is located in the crater.. "
When talking about the source in this study, they do not talk about whether it's an abiotic (non-living) or biological source. They only talk about the location of the methane release.
In the graph above, scientists from the Royal Belgian Institute for Aeronautics in Brussels, who are collaborating in the study, have divided the area around the crater of Gale into a grid. For each square, they used computer simulations to generate one million emission scenarios.
The simulations used measured methane, atmospheric circulation patterns and methane release characteristics, based on the phenomenon known as "gas infiltration". Gas infiltration occurs when trapped methane is released by subterranean formations, usually due to tectonic activity. Percentages reflect the probability that methane will come from each square of the grid.
"We have identified tectonic faults that could extend below a proposed region to contain shallow ice. Since permafrost is an excellent insulator for methane, it is possible that ice would trap methane beneath the surface and release it episodically along the faults traversing this ice."Says Giuseppe Etiope, co-author of the National Institute of Geophysics and Volcanology in Rome. "Remarkably, we have seen that the atmospheric simulation and the geological evaluation, carried out independently of each other, suggested the same region of origin of the methane.. "
Methane on Mars is always a puzzle. But the pieces begin to nestle. Now that another spacecraft, the Trace Gas Orbiter (TGO) is on Mars, we can expect the puzzle to be even more complex.
TGO is a joint mission of the European Space Agency and Roscosmos. He will do the most detailed analysis of the atmosphere of Mars. He arrived on Mars and started operating in 2016, but it is only recently that methane research has begun.
As for the source of methane on Mars, it will be necessary to wait. We do not yet know how it was produced and whether living organisms are responsible or not.
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