Methane gas on Mars may represent signs of past or present extraterrestrial life—or it could simply come from non-living geological processes. Scientists aim to solve that Martian mystery by studying methane-producing organisms living within remote wells in the Middle Eastern country of Oman.

The Omani wells go down hundreds of meters beneath the Earth’s surface to reach rock layers that store underground water. Such environments, where rocks from our planet’s mantle are in contact with water, could provide clues about the possible past or present habitability of planets such as Mars, says Alexis Templeton, a geologist and microbiologist at the University of Colorado at Boulder. She and her colleagues discovered the existence of tiny microbes capable of making methane in water samples taken from the wells. Their finding marks a first step toward better understanding how methane is produced in such underground environments.

“We were excited to know that we definitely can detect methanogens — organisms that can make methane — and we can detect methane,” says Templeton. “But we can’t make that causal link yet.”

Nobody knew if any life actually existed deep within the wells. But in the winter of 2014, Templeton and her colleagues gained the Omani government’s permission to collect water samples and drill cuttings from the well sites. They detailed their research results in the February 2016 online issue of the journal Geochimica et Cosmochimica Acta. The work was supported by the NASA Astrobiology Institute element of the NASA Astrobiology Program.