Chemistry

Mars methane hunt comes up empty, flummoxing scientists

Colourful THEMIS false colour image of Gale Crater on Mars.
Colourful THEMIS false colour image of Gale Crater on Mars.

NASA’s Curiosity rover has detected methane at Mars’s Gale crater (which is proven right here in false color).Credit score: ASU/JPL-Caltech/NASA

A spacecraft that was supposed to unravel the thriller of methane on Mars has as an alternative compounded scientists’ confusion. The European–Russian Hint Gasoline Orbiter (TGO), which started searching for the gasoline final 12 months, has but to search out any whiffs of it in Mars’s environment, says a examine printed on 10 April in Nature1.

“It’s an enormous shock,” says Dorothy Oehler, a planetary geologist on the Planetary Science Institute in Houston, Texas.

Earlier Mars missions have detected hints of methane wafting via the environment. The TGO’s failure to this point to search out the gasoline means that an unknown course of is scrubbing a lot of it from the environment quickly after it seems, says Oleg Korablev, a physicist on the House Analysis Institute in Moscow and lead writer of the examine.

Planetary scientists are eager to grasp the place Martian methane comes from as a result of most methane in Earth’s environment is produced by residing organisms. Pinning down how a lot methane is in Mars’s environment, and the place, would assist researchers to find out whether or not the gasoline comes from geological sources, reminiscent of chemical reactions in rocks, or has a extra thrilling origin — doubtlessly, Martian life2.

Scientists have repeatedly noticed methane on Mars over the previous 15 years. The reviews embrace telescopic views of a plume of methane3 in 2003 and occasional detections by NASA’s Curiosity rover because it landed at Gale crater4 in 2012. The European House Company’s Mars Categorical spacecraft has noticed the gasoline at a number of sites5 — together with a plume close to Gale6 in 2013.

Sniffing the skies

Aiming to reply the query extra definitively, the TGO arrived at Mars in 2016 and commenced accumulating atmospheric information in April 2018. Between April and August 2018, it discovered no indicators of methane, despite the fact that its devices can detect the gasoline at concentrations beneath 50 elements per trillion.

Curiosity sniffed about 500 elements per trillion of methane in mid-June 2018 — on the identical time that the TGO flew overhead with out seeing any, says Christopher Webster of the Jet Propulsion Laboratory in Pasadena, California, who runs the rover’s methane-measuring instrument. Fashions counsel that any methane plumes ought to drift upward and blend effectively into the planet’s environment inside a couple of months.

“Why do they disappear so shortly?” asks John Moores, a planetary scientist at York College in Toronto, Canada. “There’s some piece of the puzzle we’re lacking.”

Researchers are searching for solutions within the hole between Curiosity, which hunts for methane 1 metre above Mars’s floor, and the TGO, which takes its finest measurements no less than 5 kilometres above the planet. The scientists try to find out how methane might be destroyed comparatively near Mars’s floor.

One chance is that methane seeping out of the bottom is eliminated by some type of low-altitude chemical response — maybe involving mud — earlier than it could drift larger into the air, says Michael Mumma, a planetary scientist at NASA’s Goddard House Flight Middle in Greenbelt, Maryland. A workforce primarily based at Aarhus College in Denmark, which has studied how mud particles might deplete Martian methane7, will describe its concepts on 11 April on the European Geosciences Union assembly in Vienna.

In June 2018, just some months after the TGO started monitoring Mars’s environment, a large mud storm unfold throughout the planet. It obscured Mars’s environment and quickly pressured the spacecraft to focus its seek for methane on excessive elevations and latitudes.

Outlook hazy

Nonetheless, some researchers are sceptical that the TGO will ever discover the gasoline. “I’ve by no means seen a convincing detection of indigenous methane on Mars, and I don’t imagine I ever will,” says Kevin Zahnle, a planetary scientist at NASA’s Ames Analysis Middle in Moffett Area, California, who has lengthy argued that the reviews of Martian methane are observational errors.

However Oehler says that methane most likely wafts erratically out of geologically lively areas on Mars, reminiscent of these riddled with faults. With the one on-ground measurements of the gasoline coming from Curiosity, scientists merely haven’t had the prospect to look at the way it is perhaps seeping from totally different elements of the planet’s floor, or how methane is perhaps destroyed because it drifts upward8. Sushil Atreya, a planetary scientist on the College of Michigan in Ann Arbor, wish to see a collection of methane-measuring drones, dirigibles or balloons float over many areas of the Martian floor.

Within the meantime, the TGO will proceed to observe Mars’s environment via no less than 2022. Up to now, it has noticed solely a fraction of a Martian 12 months, which lasts practically two Earth years. Hints of methane may but emerge because the seasons go.

“One factor about Mars is it’s by no means boring,” says Oehler.

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