Science.-The mystery of the methane of Mars deepens with the lack of signals



ESA and Roscosmos ‘Exomars TGO (Trace Gas Orbiter) satellite has not detected any signs of methane in Mars’ atmosphere in a new data collection spanning 1.4 Red Planet years.

The mission has set new upper limits on the amount of methane, ethane, ethylene and phosphine in the Martian atmosphere, four gases called “biomarkers” that are possible signs of life.

The search for biomarkers on Mars is a main objective of the TGO. A key biomarker of interest is methane, since much of the methane found on Earth is produced by living things or geological activity, so the same may be true for Mars.

The ‘methane mystery’ on Mars has been ongoing for many years, with conflicting findings from missions including ESA’s Mars Express and NASA’s Curiosity rover that captured sporadic gas spikes and bursts in Mars’ atmosphere, fluctuations both in orbit and on the planet’s surface. signs of gas that vary with the seasons, or not seeing methane at all.

“We found no sign of the gas at all, which suggests that the amount of methane on Mars is probably even lower than previous estimates suggest,” Franck Montmessin of LATMOS, France, a co-principal investigator of the LATMOS, France, said in a statement. Atmospheric Chemistry Suite (ACS) instrument aboard the orbiter.

Because TGO instruments are highly sensitive, if methane is present, it should be in an abundance of less than 0.05 ppbv, and more likely less than 0.02 ppbv, say Franck and his colleagues. The scientists also looked for signs of methane around Curiosity’s home, Gale Crater, and found nothing, even though the rover reported the presence of methane there.

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“Curiosity measures directly on the surface of Mars, while the orbiter takes measurements a few kilometers above, so the difference between these two findings could be explained by any methane trapped in the lower atmosphere or in the vicinity of the rover,” he adds. Franck.

The apparent lack of Martian methane reported by Franck and his colleagues is supported by a paper using data from the orbiter’s NOMAD (Nadir Occultation Mars Discovery) instrument, again spanning a full Martian year and looking for methane and two other biomarkers.

“We also found no signs of methane on Mars, and we set an upper limit of 0.06 ppbv, which is consistent with TGO’s initial findings using ACS,” says the paper’s lead author, Elise Wright Knutsen, previously at the Goddard Space Flight Center. from NASA, USA, and now LATMOS, France. “In addition to looking for global methane, we also looked for columns located in more than 2,000 places on the planet and we did not detect anything, so if methane is released in this way, it must be sporadic.”


Along with methane, Elise and her colleagues looked for two other possible biomarker gases: ethane and ethylene. These molecules are expected to be produced after methane is broken down by sunlight, so they are exciting both in their own right and in the context of our quest for methane. Ethane and ethylene molecules also have a short lifespan, meaning that if they are found in a planetary atmosphere, they must have been recently released or created through a continuous process. This makes them excellent tracers for possible biological or geological activity.

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“These are the first results of ExoMars looking for these two gases,” says Elise. “We didn’t detect either one, so we set upper limits for ethane and ethylene at 0.1 and 0.7 ppbv, respectively, low but higher than our limits for methane.”

The orbiter has also been looking for phosphine, a gas that caused a lot of controversy last year when it was allegedly detected on Venus. Most of the phosphine on Earth is produced biologically, which makes it an interesting biomarker in the atmospheres of terrestrial planets.

“We didn’t find any signs of phosphine on Mars,” says Kevin Olsen of the University of Oxford, UK, and lead author of the phosphine study. “Our upper limits are similar for ethane and ethylene, between 0.1 and 0.6 ppbv.”

The search for life on Mars, or its persistent signatures, is a central goal of the ExoMars program, and the search for biomarkers in particular is a primary goal of the Trace Gas Orbiter. ExoMars’ next rover, Rosalind Franklin, to be launched in 2022, will complement TGO’s search for biomarkers by digging into the Martian surface; Underground samples are more likely to retain biomarkers, as the material is shielded from the harsh radiation environment of space.

Myrtle Frost

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