For the past two decades, planetologists have attempted to solve the mystery surrounding measurements of atmospheric methane on Mars. This includes repeated detections of this potential biosignature just above the surface of Mars’ Gale crater by NASA’s Curiosity rover.
But so far, the European Space Agency’s (ESA) ExoMars trace gas orbiter (TGO) has been found empty when searching for methane higher up in the Martian atmosphere, according to NASA.
“When the Trace Gas Orbiter arrived on board in 2016, I expected the orbiter team to report that there is a small amount of methane all over Mars,” Chris Webster, head of the Tunable Laser Spectrometer (TLS) instrument in sample analysis. at the Mars Chemistry Laboratory (SAM) aboard the Curiosity rover, said in a statement.
But now NASA thinks it has found a solution.
Because it needs a lot of power, TLS mainly operates at night when no other Curiosity instrument is operating, NASA explains. This is when the Martian atmosphere is calm at night, and methane seeping from the ground collects near the surface where Curiosity can detect it, the agency notes.
ESA’s Trace Gas Orbiter, on the other hand, requires sunlight to locate methane about 3 miles above the surface.
Thus, NASA carried out specific measurements using the TLS instrument during the day and also confirmed a non-detection of methane gas. Webster and his colleagues detailed their results this week in The Journal of Astronomy and Astrophysics.
Over the past two decades, the authors point out, measurements of Mars from a wide variety of platforms (ground telescopes, orbiters, and rover) have returned methane values from zero to about 45 parts per billion in volume.
We report that the very low levels of methane measured at night – possibly from an underground seep – are dissipated and dispersed when the sun rises, Paul Mahaffy, the SAM principal investigator, who is based at Goddard Space Flight NASA Center in Greenbelt, Maryland, told me. Our daytime measurements also give zero detection, as do those of ESA’s orbiting TGO spacecraft, he says.
As for the methane measured in Gale crater, the site that Curiosity has been exploring for nearly ten years?
“In the absence of proof of the production of methane by the rover itself, we propose that the source is planetary micro-infiltration,” write the authors.
The methane seepage from Gale Crater could come from present or past microbial life of the variety that produces methane (methanogens) on Earth, says Mahaffy. But he says it’s just as plausible that this methane could have come from underground abiotic interactions between water and rock that also produced methane.
If the methane we’re measuring comes from a methane seep in Gale Crater, Mahaffy expects this to happen in many places on Mars as well, as there are many similar deep craters on Mars.
Methane is a stable molecule that is expected to last around 300 years on Mars before being torn apart by solar radiation, according to NASA. The agency notes that experiments are underway to test whether very low-level dust-induced electrical discharges in the Martian atmosphere could destroy methane, or whether the abundant oxygen on the Martian surface rapidly destroys methane before it can destroy methane. ‘it cannot reach the upper atmosphere.
Since we have occasionally seen large spikes of orders of magnitude more intense than most of our measurements, I encourage our European colleagues to continue to monitor this signal as they orbit Mars, says Mahaffy. The release of methane from the basement can be episodic and a sudden big burp can allow TGO detection of this transient signal, he says.
Such methane detections are too important to do otherwise since most of the methane in Earth’s atmosphere comes from microbial activity.
“But Earth teaches us that there are multiple pathways by which methane can be produced in the total absence of biology,” said Timothy Lyons, a distinguished professor of biogeochemistry at the University of California at Riverside, who did not part of the team. me. “We just don’t know yet what is the case with methane on Mars. “