Imagine a future in which Mars explorers build their own tools, fuel their own rockets, or 3-D print their own houses. Although this future might be far off, the materials for such endeavors may be waiting for us in the Red Planet’s subsurface.
One of these materials is methane, the small organic molecule composed of one carbon atom and four hydrogen atoms. On Earth, methane is the main component of natural gas, which made up about 31% of the United States’ energy consumption in 2018, according to the U.S. Energy Information Administration. If we were able to find and harness methane on Mars, along with the planet’s abundance of carbon dioxide and water, the possibilities would be endless.
“The most important thing about having methane, water, and carbon dioxide is a lot of people don’t realize that natural gas is basic feedstock for the petrochemical industry,” said Michael Max, a geologist at University College Dublin in Ireland who specializes in figuring out the economic uses of Earth’s raw materials. In other words, methane could provide a crucial raw material for plastic, a petrochemical product that could be 3-D printed into a number of objects useful for living on Mars (like tools, protective sheeting, and spaceship parts).
Methane could also provide the starting point for creating rocket fuel, Max said, which would revolutionize how we travel through space.
“Mars then would not just be a destination, Mars could be the jumping-off point for the other planets,” he said. Max presented his research on the uses for Martian methane at AGU’s Fall Meeting 2019 on 12 December.
Martian Methane Origins
Before we get too excited about the prospect of deep-space travel, first, we have to find the methane. And that might be harder than it sounds. After all, Earth’s natural gas comes from decaying organisms that settled on ocean floors billions of years ago. As those organisms were buried under many, many tons of sediment, pressure and heat caused chemical reactions that turned them into the natural gas we know today. The methane entering the atmosphere today comes from both natural and anthropogenic sources.
Methane’s story is a bit more complicated on Mars. Because we haven’t yet discovered life on the Red Planet, scientists must consider abiotic processes that produce methane, said Dorothy Oehler, a senior scientist at the Planetary Science Institute in Houston, Texas. One of those processes is called thermogenesis, wherein methane forms from organic materials heated during burial in deep basins. In this case, those organics could have been delivered to Mars by meteorites or interplanetary dust. Methane could also be stored in permafrost deep underground, in gas pockets sealed off by deep sediment, or in ice-like crystal structures called clathrates, also deep underground.
Although NASA’s Curiosity rover has periodically detected spikes of the gas in the atmosphere surrounding its home in Gale Crater, some Mars orbiters haven’t been able to corroborate those readings—so methane’s existence in the Mars subsurface is still under active debate.
Methane Treasure Hunt
Oehler and her colleagues are working on finding the methane, and they also presented at AGU’s Fall Meeting. As a former petroleum exploration geologist, Oehler is well versed in spotting geological formations that hint at subsurface stocks of natural gas. She uses image data from Mars orbiters while studying methane in the atmosphere using data from instruments aboard the European Space Agency’s ExoMars and Mars Express orbiters and from ground level from NASA’s Curiosity rover in Gale Crater.
Oehler looks for places that could host deep basins where methane could form via thermogenesis and places where water ice in the subsurface could form permafrost, locking methane in ice. She and her team also look for geological formations like mud volcanoes, which on Earth provide seepage pathways for methane percolating up from the subsurface.
For example, Mars’s Acidalia Planitia and Utopia Planitia, both situated in Mars’s northern lowlands, could be great candidates for methane storage, Oehler said. These relatively smooth plains (when compared to Mars’s southern highlands) could indicate resurfacing from ancient floods or volcanism—two processes that could trap ancient methane under sediment. Acidalia Planitia also hosts mysterious mound-shaped features, which Oehler thinks could be long-dead mud volcanoes.
The Future of Methane Detection
But scientists would still need to detect the methane, and orbiter detections haven’t been definitive. Because methane releases are so infrequent and because the handful of Mars orbiters can’t cover every spot on Mars at all times, methane detection has been elusive.
“Since Mars does not have a pervasive biosphere which generates much of the methane on Earth, occasional seeps could be easy to miss by occasional observations made by Earth-based telescopes or orbiters,” Oehler said.
Now that Oehler and her colleagues have pinpointed spots on Mars where methane could be trapped or seeping out, the next step would be to instruct orbiters to observe those spots more frequently. With more frequent observations, “actual sites of methane release may be identified and then singled out for future exploration, using in-ground collection,” she said.