Wednesday, July 14, 2021

Scientists are getting closer to solving the methane mystery on Mars.

rovermars
Image NASA

Scientists and non-scientists alike have been intrigued by reports of methane detections on Mars. Microbes that aid in the digestion of plants produce a substantial amount of methane on Earth. When livestock expel or belch gas into the air, the digesting process is complete.

While there are no livestock, goats, or sheep on Mars, the discovery of methane is significant because it could mean that bacteria have lived or now live there. Methane, on the other hand, could be produced by geologic processes involving the interaction of rocks, water, and heat without having anything to do with germs or biology.

Before scientists can pinpoint the origins of methane on Mars, they must first answer a vexing question: why do certain equipment detect the gas while others do not? For example, NASA's Curiosity rover has discovered methane just above the surface of Gale Crater on many occasions. However, the European Space Agency's (ESA) ExoMars mission's Trace Gas Orbiter, TGO, has not identified methane in the Martian atmosphere.

"The Trace Gas Orbiter was expected to indicate that there is a modest quantity of methane everywhere on Mars," Chris Webster, director of the Tunable Laser Spectrometer (TLS) on the SAM instrument, a chemistry laboratory aboard the Curiosity rover, said.

In Gale Crater, the TLS has averaged less than a half per billion by volume of methane. This is the same as a pinch of salt diluted in an Olympic-size pool. Disturbing peaks of up to 20 parts per billion by volume have been observed during these measurements.

"However, I was shocked when the European team said it had found no methane," said Webster, who works at NASA's Jet Propulsion Laboratory in Southern California.

The European orbiter was built to be the most accurate in the world in measuring methane and other gases. At the same time, Curiosity's TLS is so precise that it will be used to identify fires on the International Space Station before they spread and to monitor oxygen levels in astronaut suits. It's also approved for use in power plants, oil pipelines, and military aircraft, where pilots can check the amounts of oxygen and carbon dioxide in their helmets.

Nonetheless, Webster and the SAM team were taken aback by the European orbiter's findings and set out to investigate TLS readings on Mars right away.

Some analysts speculated that the rover was expelling gas on its own. Webster explained, "So we looked at relationships with rover orientation, dirt, rock crushing, wheel degradation, you name it." "I can't express how meticulously the team has scrutinized every last element to ensure that those metrics are accurate, which they are."

While the SAM team attempted to validate their methane detections, planetary scientist John E. Moores of York University in Toronto, a member of Curiosity's science team, issued an exciting prediction for 2019. "I took a very Canadian approach to this," Moores explained, "in that I addressed the question, 'What if Curiosity and TGO are correct?"

Moores and other Curiosity group members investigating wind patterns in Gale Crater theorized that the difference in methane measurements is due to the time of day they are obtained. TLS is only active at night, when other Curiosity instruments aren't working, because it requires a lot of power. Moores pointed out that because the Martian atmosphere is silent at night, methane escaping from the ground gathers near the surface, where Curiosity can detect it.

TGO, on the other hand, necessitates the use of sunlight to locate methane around 5 kilometers above the ground. "During the day, any atmosphere near a planet's surface goes through a cycle," Moores explained. Warm air rises and cold air falls when the Sun's heat stirs the atmosphere. As a result, methane trapped near the surface at night mixes with the rest of the atmosphere during the day, diluting it to undetectable levels. Moores explained, "I understood that no instrument, especially one in orbit, would see anything."

The Curiosity crew chose to put Moores' prediction to the test right away by taking the first high-precision diurnal measurements. TLS took three measurements of methane over the course of a Martian day, combining a nocturnal measurement with two daylight measurements. SAM took in Martian air for two hours at a time during each experiment, continually eliminating carbon dioxide, which makes up 95 percent of the planet's atmosphere. TLS was able to quantify a concentrated sample of methane by repeatedly running an infrared laser beam across it, one that was calibrated to employ an exact wavelength of light that is absorbed by the methane.

"Our two daytime observations validated John's prediction that methane should effectively decrease to zero throughout the day," said Paul Mahaffy, principal investigator for SAM, which is based at NASA's Goddard Space Flight Center in Greenbelt, Maryland. The TLS measurement taken at night falls well within the team's determined average. "So that's one approach to settle this huge gap," Mahaffy remarked.

While this study reveals that methane emissions on the surface of Gale Crater increase and decrease throughout the day, scientists have yet to solve the entire methane problem on Mars. Methane is a long-lasting chemical that will last for roughly 300 years on Mars before being destroyed by solar radiation. If methane is continually escaping from all similar craters, as scientists think given Gale's geological similarity, enough should have accumulated in the atmosphere for the TGO satellite to detect it. In fewer than 300 years, scientists believe that something is depleting the methane.

Investigations are ongoing to see if dust-induced low-level electrical discharges in the Martian atmosphere may demolish methane, or if abundant oxygen on the Martian surface can quickly destroy methane before this reaches the higher atmosphere.

Curated By Gerluxe

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