NASA’s Curiosity Rover has discovered methane in Gale Crater on Mars, a surprising find since there are no signs of life on the planet. Scientists are investigating geological sources and seasonal patterns of these emissions, with methane levels showing unusual fluctuations and disappearing during the day. (Artist’s concept.) Credit: SciTechDaily.com
A recent article may help explain why a portable chemistry lab is underway
” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>NASA‘s Curiosity rover has continually sniffed out traces of the gas near the surface of Gale Crater.
The most surprising revelation from NASA’s Curiosity Mars Rover – that methane is seeping from the surface of Gale Crater – has scientists scratching their heads.
Living things produce most of the methane on Earth. But scientists have not found convincing signs of current or ancient life
” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>March, and therefore did not expect to find methane there. Still, the portable chemistry lab aboard Curiosity, known as SAM, or Sample Analysis at Mars, has been constantly sniffing for traces of the gas near the surface of Gale Crater, the only place on Mars’ surface where methane has so far been detected. Its likely source, researchers hypothesize, is geological mechanisms involving water and rocks deep underground.
Filled with salt lakes, the Quisquiros Salt Flat in South America’s Altiplano region represents the type of landscape that scientists believe may have existed in Gale Crater on Mars, which NASA’s Curiosity Rover is exploring. Credit: Maksym Bocharov
If that was the whole story, it would be easy. However, SAM has found that methane behaves in unexpected ways in Gale Crater. It appears at night and disappears during the day. It fluctuates seasonally, sometimes peaking at levels 40 times higher than usual. Surprisingly, the methane does not accumulate in the atmosphere either: ESA’s (den
” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>European Space Agency) The ExoMars Trace Gas Orbiter, which was sent to Mars specifically to study the gas in the atmosphere, has not detected any methane.
Why do some scientific instruments detect methane on the Red Planet while others do not?
“It’s a story with many twists and turns,” said Ashwin Vasavada, Curiosity’s project scientist at NASA’s Jet Propulsion Laboratory in Southern California, who is leading Curiosity’s mission.
Methane keeps Mars scientists busy with lab work and computer modeling projects aimed at explaining why the gas behaves strangely and is only detected in Gale Crater. A research team from NASA recently shared an interesting proposal.
This is a sample of apparent Martian regolith, which is “soil” made of broken rock and dust. It is one of five samples that researchers infused with varying concentrations of a salt known as perchlorate that is common on Mars. They exposed each sample to Mars-like conditions in the Mars Simulation Chamber at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The brittle lumps in the sample above show that a seal of salt did not form in this sample because the salt concentration was too low. Credit: NASA/Alexander Pavlov
Reporting in a March paper i Journal of Geophysical Research: Planets, the group suggested that methane — regardless of how it’s produced — could be sealed under solidified salt that can form in Martian regolith, which is “soil” made of broken rock and dust. As temperatures rise during warmer seasons or times of day, weakening the seal, methane can seep out.
Led by Alexander Pavlov, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, the researchers suggest that the gas can also erupt in flares when seals rupture under the pressure of, say, a rover the size of a small SUV driving over it. The team’s hypothesis could help explain why methane is only detected in Gale Crater, Pavlov said, because it is one of two places on Mars where a robot is moving and drilling the surface. (The other one is Jezero Craterwhere NASA’s Perseverance rover works, even though that rover has no methane-detecting instrument.)
This image is of another sample of apparent Martian “soil” after it was removed from the Mars simulation chamber. The surface is sealed with a solid salt crust. Alexander Pavlov and his team found that a seal formed after a sample spent three to 13 days in Mars-like conditions, and only if it had a 5% to 10% perchlorate salt concentration. The color is lighter in the center where the sample was scratched with a metal pick. The light color indicates a drier soil below the top layer, which absorbed moisture from the air as soon as the sample was removed from the simulation chamber and turned brown. Credit: NASA/Alexander Pavlov
Pavlov traces the origin of this hypothesis to an unrelated experiment he led in 2017, which involved growing microorganisms in a simulated Martian permafrost (frozen soil) infused with salt, as much of Martian permafrost is.
Pavlov and his colleagues tested whether bacteria known as halophiles, which live in saltwater lakes and other salt-rich environments on Earth, could thrive under similar conditions on Mars.
The microbe-growing results proved inconclusive, he said, but the researchers noticed something unexpected: The top layer of soil formed a salt crust when salty ice sublimated, turning from a solid to a gas, leaving the salt behind.
“We didn’t think much of it at the moment,” Pavlov said, but he remembered the crust in 2019, when SAM’s tunable laser spectrometer detected a methane burst no one could explain.
“That’s when it clicked in my mind,” Pavlov said. And that’s when he and a team began testing the conditions that could form and crack hardened salt seals.
Curiosity sought to answer the question: Did Mars ever have the right environmental conditions to support tiny life forms called microbes? Early in its mission, Curiosity’s science tools found chemical and mineral evidence of previously habitable environments on Mars. It continues to explore the rock record from a time when Mars could have been home to microbial life. Credit: NASA
Pavlov’s team tested five samples of permafrost infused with different concentrations of a salt known as perchlorate that is widespread on Mars. (There is likely no permafrost in Gale Crater today, but the seals could have formed long ago when Gale was colder and icier.) The researchers exposed each sample to different temperatures and air pressures inside a Mars simulation chamber at NASA Goddard.
Periodically, Pavlov’s team injected neon, a methane analog, under the soil sample and measured the gas pressure below and above it. Higher pressures during the test suggested that the gas was trapped. Ultimately, a seal formed under Mars-like conditions within three to 13 days only in samples with 5% to 10% perchlorate concentration.
That’s a much higher salt concentration than what Curiosity has measured in Gale Crater. But regolith there is rich in another type of salt minerals called sulfates, which Pavlov’s team wants to test alongside to see if they can also form seals.
Improving our understanding of methane generation and destruction processes on Mars is an important recommendation from 2022 NASA Planetary Mission Senior Review, and theoretical work such as Pavlov’s is essential to this effort. But scientists say they also need more consistent methane measurements.
SAM only sniffs for methane several times a year because it is otherwise busy doing its primary job of drilling samples from the surface and analyzing their chemical composition.
“Methane experiments are resource intensive, so we have to be very strategic when we decide to do them,” said Goddard’s Charles Malespin, SAM principal investigator.
But testing how often methane levels increase, for example, would require a new generation of surface instruments that measure methane continuously from many locations across Mars, researchers say.
“Some of the methane work will have to be left to future spacecraft that are more focused on answering these specific questions,” Vasavada said.
Reference: “Formation and Stability of Saline Earth Seals Under Mars-Like Conditions. Implications for Methane Variability on Mars” by Alexander A. Pavlov, James Johnson, Raul Garcia-Sanchez, Ariel Siguelnitzky, Chris Johnson, Jeffrey Davis, Scott Guzewich, and Prabhakar Misra, March 9, 2024, Journal of Geophysical Research: Planets.
DOI: 10.1029/2023JE007841
Curiosity was built by
” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>JPL, which is managed by Caltech in Pasadena, California. JPL is leading the mission on behalf of NASA’s Science Mission Directorate in Washington.
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