Mars' subsurface is 'burping' out methane and scientists aren't sure why

News
By Stefanie Waldek
published

Salt might play a key role in the mysterious behavior of methane seeps on Mars.

image of a large whitish rover on the surface of mars, surrounded by rocks and red dirt.
NASA's Mars Curiosity rover took this selfie on June 13, 2018. The six-wheeled robot has repeatedly detected methane during its exploration of Mars' Gale Crater, and scientists are still trying to figure out where the gas is coming from. (Image credit: NASA/JPL-Caltech)

Since 2012, NASA's Curiosity rover has repeatedly detected methane on Mars, specifically near its landing site inside the 96-mile-wide (154 kilometers) Gale Crater. 

But that Mars methane is behaving erratically. It only appears at night, it fluctuates seasonally and it spikes unexpectedly to levels 40 times higher than usual. To make things more puzzling, the gas isn't present in appreciable amounts high in the Martian atmosphere, and it hasn't been detected near the surface in other Red Planet locales. So what's going on at Gale Crater?

A group of NASA researchers led by planetary scientist Alexander Pavlov may now have at least a partial answer. The team suggests the Mars methane is trapped beneath a crust of solidified salt within the regolith at Gale. Warm daytime temperatures could weaken the crust, allowing methane to slip out at night. And the weight of a heavy rover driving over the crust could crack the crust, too, allowing methane to burst out in a concentrated puff. (Yes, it's akin to burping a baby.)

Related: NASA's Mars rover Curiosity: The ultimate guide

The researchers tested their hypothesis here on Earth, using a simulated Martian regolith; a salt called perchlorate, which exists widely on Mars; and neon as an analog for methane. Their tests, performed inside a Mars simulation chamber at NASA's Goddard Space Flight Center in Maryland, showed that a salt crust could form under certain conditions, trapping methane beneath it.

While a layer of solidified salt might explain the irregular behavior of Martian methane, scientists still don't know why methane even exists on Mars in the first place. On Earth, methane is primarily produced by living organisms — but we still haven't found signs of life on Mars. 

And, to be clear, methane is not a surefire sign of life; the gas can be produced by geological processes as well.

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"It's a story with a lot of plot twists," Ashwin Vasavada, Curiosity's project scientist at NASA's Jet Propulsion Laboratory in Southern California, said in a statement. "Some of the methane work will have to be left to future surface spacecraft that are more focused on answering these specific questions."

A paper on the team's research was published on March 9, 2024, in the Journal of Geophysical Research.

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Stefanie Waldek
Stefanie Waldek
Contributing writer

Space.com contributing writer Stefanie Waldek is a self-taught space nerd and aviation geek who is passionate about all things spaceflight and astronomy. With a background in travel and design journalism, as well as a Bachelor of Arts degree from New York University, she specializes in the budding space tourism industry and Earth-based astrotourism. In her free time, you can find her watching rocket launches or looking up at the stars, wondering what is out there. Learn more about her work at www.stefaniewaldek.com.

9 Comments Comment from the forums
  • Unclear Engineer
    And then there is this https://www.livescience.com/space/mars/hundreds-of-black-spiders-spotted-in-mysterious-inca-city-on-mars-in-new-satellite-photos .

    Get past the click bait headline, and see the description of the environmental physics that create these patterns.
    Reply
  • HobartStinsonian
    I’ll take exception to this sentence, “On Earth, methane is primarily produced by living organisms”. On Earth a huge majority of methane comes naturally from inside Earth’s crust. Natural gas. There is every reason to believe that the crust of Mars may also contain natural gas. When methane was captured inside the Earth during the formation of the solar system, why not also in other planets? And on Titan too?
    Reply
  • Sarah Newton
    HobartStinsonian said:
    I’ll take exception to this sentence, “On Earth, methane is primarily produced by living organisms”. On Earth a huge majority of methane comes naturally from inside Earth’s crust. Natural gas. There is every reason to believe that the crust of Mars may also contain natural gas. When methane was captured inside the Earth during the formation of the solar system, why not also in other planets? And on Titan too?
    And where does "natural gas" come from?
    Reply
  • Unclear Engineer
    Sarah Newton said:
    And where does "natural gas" come from?
    That is sort of an interesting question.

    On Earth, the assumption is that it comes from decaying biological matter that has been transported below and trapped below the surface by various geological processes, including silt layer buildup over swamps, plate tectonics, etc.

    But, if there always was no life on Mars, then that could not account for what we see on Mars. The methane there would not be from photosynthesis of carbon dioxide and water.

    Methane is also common in other planetary atmospheres where we don't think any life has ever existed. We think it forms in space and gets compacted into planets along with the other materials.

    So, could some of the methane oozing out of the Earth be "primordial" instead of biological? Maybe. But, the geologic evidence is that most of it can be explained by biological processes.

    The radioactive isotopes of hydrogen and carbon are too short lived to look for the "age" of very old methane. But, carbon has 2 stable isotopes, atomic weights 12 and 13. C-13 is rare on Earth. Somebody might try to used the ratio of C-13 to C-12 to distinguish different origins of some methane, but I have never heard of that.
    Reply
  • HobartStinsonian
    Unclear Engineer said:
    That is sort of an interesting question.

    On Earth, the assumption is that it comes from decaying biological matter that has been transported below and trapped below the surface by various geological processes, including silt layer buildup over swamps, plate tectonics, etc.

    But, if there always was no life on Mars, then that could not account for what we see on Mars. The methane there would not be from photosynthesis of carbon dioxide and water.

    Methane is also common in other planetary atmospheres where we don't think any life has ever existed. We think it forms in space and gets compacted into planets along with the other materials.

    So, could some of the methane oozing out of the Earth be "primordial" instead of biological? Maybe. But, the geologic evidence is that most of it can be explained by biological processes.

    The radioactive isotopes of hydrogen and carbon are too short lived to look for the "age" of very old methane. But, carbon has 2 stable isotopes, atomic weights 12 and 13. C-13 is rare on Earth. Somebody might try to used the ratio of C-13 to C-12 to distinguish different origins of some methane, but I have never heard of that.
    Methane is detected in Titan and its origin is not biological. Methane is detected in interstellar gas clouds, not biological. It was likely in the cloud of gas and dust when the solar system formed. Same with all elements inside all the planets. Interesting that helium sources are almost always associated with natural gas wells. Not biological, eh? Why assume living organisms were transformed into coal, oil, and gas, when the precursor elements don’t balance with the product elements?
    Reply
  • Unclear Engineer
    Helium is definitely created inside the Earth - by radioactive decay that involves alpha particle emissions. Alpha particles are just the nuclei of Helium-4 atoms. The uranium and thorium in the Earth are decaying to lead in processes that produce a lot of intermediate elements, and along the way, each initial atom of uranium or thorium releases 6, or 7, or 8 alpha particles that become He-4 atoms. See https://en.wikipedia.org/wiki/Decay_chain .

    So, that does collect in places in the crust that also collect methane, such as gas and oil deposits. And, we "mine helium" by separating it out when we extract the oil and methane.

    So, could we tell if any of the methane that we are extracting is primordial, rather then the result of photosynthesis creating it from water and carbon dioxide taken from the atmosphere and eventually buried by geological processes?

    Here is a study of isotopic ratios for carbon and oxygen in the Martian atmosphere: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021JE006992 . It provides some discussion of the complexities of the natural processes that affect isotopic ratios.
    Reply
  • Ken Fabian
    HobartStinsonian - The sedimentary geology of oil and gas deposits on Earth support their formation out of biological materials that came from the surface, by observable processes. The existence of non-biological methane on Mars doesn't mean methane on Earth must be abiotic - nor does the abundance of methane on Earth with biological origins mean that Earth can't have sources of methane that are abiotic.
    Reply
  • Torbjorn Larsson
    The NASA article by Lonnie Shekhtman is a bit more informative:
    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 Curiosity has measured in Gale Crater. But regolith there is rich in a different type of salt minerals called sulfates, which Pavlov’s team wants to test next to see if they can also form seals.
    https://science.nasa.gov/solar-system/planets/mars/why-is-methane-seeping-on-mars-nasa-scientists-have-new-ideas/
    Reply
  • Torbjorn Larsson
    Unclear Engineer said:
    So, could some of the methane oozing out of the Earth be "primordial" instead of biological? Maybe. But, the geologic evidence is that most of it can be explained by biological processes.

    The radioactive isotopes of hydrogen and carbon are too short lived to look for the "age" of very old methane. But, carbon has 2 stable isotopes, atomic weights 12 and 13. C-13 is rare on Earth. Somebody might try to used the ratio of C-13 to C-12 to distinguish different origins of some methane, but I have never heard of that.
    The kerogen cycle of sedimentary organic material compression and heat conversion has long been known to produce most of modern Earth's natural gas deposits. Coal mining show the fossils and the associated oil/gas production. The atmospheric methane has today mostly industrial but still a hefty biosphere production basis.
    The known sources of methane are predominantly located near the Earth's surface. Two main processes that are responsible for methane production include microorganisms anaerobically converting organic compounds into methane (methanogenesis), which are widespread in aquatic ecosystems, and ruminant animals. Other natural sources include melting permafrost, wetlands, plants, and methane clathrates.
    https://en.wikipedia.org/wiki/Atmospheric_methane
    It is likely Hadean Earth contained primordial methane which was converted into carbon dioxide as atmospheric hydrogen was lost to space. This is an active research area for studies of astronomical biosignatures.

    Since cellular metabolism prefer the less massive C12 the negative C13/C12 fractional ratio (compared to a reference) has long been used to identify biotic sources for methane.
    12C and 13 C are measured as the isotope ratio δ13C in benthic foraminifera and used as a proxy for nutrient cycling and the temperature dependent air–sea exchange of CO2 (ventilation).
    https://en.wikipedia.org/wiki/Isotopes_of_carbon
    Reply