So, where was the methane from Mars?

Work of art: TGO

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Work: TGO looks through the atmosphere and identifies the molecules by the way they absorb sunlight

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The mystery of methane on Mars became much more complicated.

The gas, which on Earth is largely produced by living things, has previously been detected on the Red Planet by remote observation, and on the ground by NASA's Curiosity rover.

But the most sensitive search on Mars so far, made by a joint European-Russian satellite, has gone blank.

And this Trace Gas Orbiter, as it is called, is able to see methane at incredibly low levels.

Even when the concentration is only a few tens of molecules in every trillion molecules of Martian air, the TGO should be able to identify the presence of CH4, if it is there.

The fact that the satellite failed to explore the atmosphere in April to August of last year raises some difficult questions and some fascinating possibilities.

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Inevitably, some people will argue that previous detections were confused, but Oleg Korablev of the Space Research Institute of the Russian Academy of Sciences in Moscow will not be among them.

"We prefer not to criticize the results of others, we can only affirm the accuracy of our results," the TGO scientist told the BBC.

"We simply report the data and let the theorists try to explain what is happening."

Curiosity sampling in 2013 in the Equatorial Gale crater found methane peaks in the air at a few parts per billion.

This was ostensibly confirmed by concurrent observations from orbit by another satellite, the European spacecraft Mars Express.

So, if it is accepted that methane was actually there in 2013 and that the TGO is the gold standard on Mars today, scientists are required to identify a process not yet recognized that can quickly remove CH4 from the atmosphere in a short space of time.

This is the working hypothesis, says Dr. Manish Patel, another TGO scientist from the Open University of the United Kingdom.

"If we take the measurements before their nominal value, and obviously we believe in our own results, then there is something that is happening in the atmosphere between those two points in time, and it is something we did not predict.

"We expect methane to remain in the atmosphere of Mars for hundreds of years, it is destroyed by sunlight, but it is destroyed on relatively long time scales in terms of human observation." What had been there before should still be there today, even if a diluted level. "

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NASA / JPL-Caltech / MSSS

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Curiosity encountered both peaks and a methane background level shortly after landing in 2012

It's as if we now have a double puzzle.

People had been debating where methane could arise on the planet, with the tempting prospect that the microbial producers of CH4 could be the source. Now, they will have to debate where the methane goes; What could be their "sinks".

A kind of chemical interaction would be an answer, but Håkan Svedhem, the project scientist for the European Space Agency at TGO, says that people should not be discouraged by the possibilities of life on the planet if it is finally determined that methane is not I presented.

"We have a bit of methane fixation because on Earth we all know that more than 95% of methane comes from biological sources, but there are abundant forms of life that do not produce methane," he told BBC News.

The Orbiter of Trace Gas arrived on the Red Planet in October 2016, but then it took another year to maneuver in its proper scientific orbit at an altitude of 400 km above the surface.

Starting in April of last year, he began his systematic search of the atmosphere, using the onboard spectrometers NOMAD and ACS.

These measure the constituents of the Martian air looking through the atmosphere towards the sun. Different molecules absorb light in a characteristic way.

The accuracy of this solar hiding method allows TGO to set an upper limit for methane at only 12 parts per trillion. In other words, if the methane is there, it has to have a lower concentration than this.

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Title of the mediaHåkan Svedhem: "We have to find some method to destroy methane"

The mission team reports its latest observations here at the General Assembly of the European Union of Geosciences.

The group also has some articles that are published in the journal Nature and in the Proceedings of the Russian Academy of Sciences.

Other results include an exquisite description of how the water was brought into the atmosphere during the recent global dust storm on the planet; and a new map of water below the surface derived from the satellite's neutron spectrometer.

This map has a higher resolution than any previous study and, apart from the permafrost, obviously rich in water, of the polar regions, it detects some "wet" regions previously unknown at the equator.

These could be important for future surface robots looking for evidence of current microbial life and for astronauts who need local water resources.

[email protected] And follow me on Twitter: @BBCAmos

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