Planetary scientists perk up whenever methane is mentioned. Methane is produced by living things on Earth, so it\u2019s considered to be a potential biosignature elsewhere. In recent years, MSL Curiosity detected methane coming from the surface of Gale Crater on Mars. So far, nobody\u2019s successfully explained where it\u2019s coming from. <\/p>\n
NASA scientists have some new ideas. <\/p>\n
<\/p>\n Ever since Curiosity landed on Mars in 2012, it\u2019s been sensing methane. But the methane displays some odd characteristics. It only comes out at night, it fluctuates with the seasons, and sometimes, the amount of methane jumps to 40 times more than the regular level. <\/p>\n The ESA\u2019s ExoMars Trace Gas Orbiter entered a science orbit around Mars in 2018, and scientists fully expected it to detect methane in the planet\u2019s atmosphere. But it didn\u2019t, and it has never been detected elsewhere on Mars\u2019 surface. <\/p>\n If life was producing the methane, it appears to be restricted to the subsurface under Gale Crater. <\/p>\n There\u2019s no convincing evidence that life exists on Mars. It may have in the past, and it\u2019s possible that some extant life clings to a tenuous existence in subsurface brines or something. But we lack evidence, so life is basically ruled out as the methane source. Especially since the evidence shows life would have to be under Gale Crater and nowhere else. <\/p>\n Scientists have been trying to determine the source of methane, but so far, they haven\u2019t come up with a specific answer. It has something to do with subsurface geological processes involving water, most likely. <\/p>\n \u201cIt\u2019s a story with a lot of plot twists,\u201d said Ashwin Vasavada, Curiosity\u2019s project scientist at NASA\u2019s Jet Propulsion Laboratory in Southern California, which leads Curiosity\u2019s mission.<\/p>\n Alexander Pavlov is a planetary scientist at NASA\u2019s Goddard Space Flight Center who leads a group of NASA scientists studying the Martian Methane Mystery. In recent research, they suggested that the methane is stored underground. They didn\u2019t explain what produced it, but they showed that methane can be sealed underground by salt solidified in the Martian regolith. <\/p>\n They suggested that the methane could be released from its subsurface reservoir by the weight of the Curiosity rover itself. The rover\u2019s weight could break the salt seal and release methane in puffs. That\u2019s an interesting proposition, but it doesn\u2019t explain the seasonal and diurnal fluctuations. That makes sense since the Gale Crater is one of only two regions where a rover is working. The other is Jezero Crater, where the Perseverance Rover is working, but it doesn\u2019t have a methane detector. (Neither will the ESA\u2019s Rosalind Franklin rover, which is scheduled to land on Mars in 2029.)<\/p>\n The research group addressed those fluctuations by suggesting that seasonal and daily heating could also break the seal and release methane. <\/p>\n Their potential explanations stem from research Pavlov conducted in 2017. He grew bacteria called halophiles, which grow in salty conditions, in simulated Martian permafrost. The simulated soil was infused with salt, replicating conditions on much of Mars. The microbe growth was inconclusive, but the researchers noticed something else. As the salty ice sublimated, a layer of solidified salt remained, forming a crust.<\/p>\n \u201cWe didn\u2019t think much of it at the moment,\u201d Pavlov said.<\/p>\n But he remembered it when MSL Curiosity detected an unexplained burst of methane on Mars in 2019. <\/p>\n \u201cThat\u2019s when it clicked in my mind,\u201d Pavlov said. Then, he and a team of researchers began testing conditions that could form the hardened salt seals and then break them open.<\/p>\n Perchlorate is a chemical salt that\u2019s widespread on Mars. Pavlov and his fellow researchers recreated different simulated Martian permafrosts with varying amounts of perchlorate. Inside a Mars simulation chamber, they subjected the samples to different temperatures and atmospheric pressures to see if they would form seals. <\/p>\n In their experiments, they used neon as a methane analog and injected it under the soil. Then, they measured the gas pressure below and above the soil. They found that the pressure was higher under the soil, meaning the gas was being trapped by the salty permafrost. Furthermore, they found that seals formed in samples containing as little as 5% or 10% perchlorate, and they formed within 3 to 13 days. Those are compelling results. <\/p>\n While 5-10% perchlorate doesn\u2019t sound like much, it\u2019s actually a higher concentration than in Gale Crater, where the methane has been detected. But perchlorate isn\u2019t the only salt in Martian regolith. It also contains sulphates, another type of salt mineral. Pavlov says he and his team will test sulphates next for their ability to form a seal. <\/p>\n The Martian Methane Mystery is commanding a lot of attention. It\u2019s a juicy mystery, and once it\u2019s solved, our understanding of methane as a biosignature or false positive will be much improved. NASA\u2019s 2022 Planetary Mission Senior Review recommended that the issue of methane production and destruction at Mars be investigated further. <\/p>\n The type of work that Pavlov and his colleagues are doing is important, but it\u2019s being held back. Pavlov says that they need more consistent methane measurements. The problem is that Curiosity\u2019s SAM (Sample Analysis at Mars) instrument, which senses the methane, is busy with other tasks. It only checks for methane a few times per year. It\u2019s mostly occupied with drilling samples and testing them, a critical and time-consuming part of the rover\u2019s mission.<\/p>\n \u201cMethane experiments are resource intensive, so we have to be very strategic when we decide to do them,\u201d said Goddard\u2019s Charles Malespin, SAM\u2019s principal investigator.<\/p>\n Curiosity\u2019s mission wasn\u2019t designed to measure methane fluctuations. In 2017, NASA said its SAM instrument only sampled the atmosphere 10 times in 20 months. That\u2019s a very inconsistent sample that leaves lots of unanswered questions. <\/p>\n Scientists think another mission is needed to advance their understanding of Martian methane. Rather than one sensor taking irregular methane readings from one location, we need multiple testing stations on the surface that regularly monitor the atmosphere. Nothing like it is in the works. <\/p>\n \u201cSome of the methane work will have to be left to future surface spacecraft that are more focused on answering these specific questions,\u201d Vasavada said.<\/p>\n![\"This](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2024\/05\/Mars-Methane-salt-cap-1024x793.jpg\")
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