Astronomy
The Potential for Methanogenic Life in Mars' Subsurface
Quick fact
Methane has been repeatedly detected in Mars' atmosphere, but in puzzlingly variable amounts—and at least some of it could be produced by microbes living deep underground. However, the most famous detection by the Curiosity rover was later found to be likely contaminated by Earthly methane from the rover itself.
Why this is interesting
When you think of life on Mars, you might picture little green men—but what if the real clue is a simple gas that you cook with on Earth? Why would that gas make astrobiologists rethink everything?
Read the full explanation
Understanding The Potential for Methanogenic Life in Mars' Subsurface
To understand why methanogenic life might exist underground on Mars, first compare it to Earth. On our planet, certain microbes called methanogens live in oxygen-free places like swamps, the guts of cows, and deep rock fractures. They don't need sunlight or organic food from plants—they can survive by 'eating' hydrogen and carbon dioxide, producing methane as waste. Now imagine Mars: its surface is frozen, bombarded with radiation, and drying out. But kilometers below the surface, the pressure and warmth might let liquid water exist in pores and cracks of rock. There's also evidence of hydrogen produced when water reacts with certain minerals, and carbon dioxide is abundant in the atmosphere. So if you put those ingredients together—H2, CO2, and a watery, oxygen-free place—you have a recipe for methanogenesis. The methane would then seep up to the surface through fractures, which is why we detect it in the atmosphere.
A deeper explanation
The mechanism hinges on the metabolic pathway called methanogenesis. It's an anaerobic (oxygen-avoiding) form of respiration that uses a series of enzymes to combine hydrogen (H2) with carbon dioxide (CO2) to produce methane (CH4) and water. This reaction releases energy that microbes can use to live. On Mars, several non-biological processes also make methane, like ultraviolet light breaking down organic molecules or volcanic activity. But if the methane we see is coming from a biological source, it must be protected from the surface's harsh conditions. The subsurface provides that shield: it blocks radiation, maintains stable temperatures, and could hold liquid water in brine-filled fractures. The potential is exciting because on Earth, such deep subsurface communities thrive without sunlight, relying solely on chemical energy. If Mars ever had life, it might have retreated to these hidden aquifers as the surface became inhospitable. Detecting methane spikes, especially with isotopic ratios similar to biological production, could be a strong hint. But the story is still open; many mysteries remain about the exact sources and sinks of Martian methane, which is why future missions like the ExoMars rover are designed to drill and sniff for such signs.