Strange gas signature on Mars may help explain methane mystery

An artist's depiction of the European-Russian Trace Gas Orbiter circling Mars.
An artist's depiction of the European-Russian Trace Gas Orbiter circling Mars. (Image credit: ESA/ATG medialab)

A Mars orbiter run by the European Space Agency (ESA) has sniffed out two never-before-seen chemical signatures in the Red Planet's atmosphere. This discovery could solve a longstanding Martian methane mystery.

Both detections come from ESA's Trace Gas Orbiter, which launched in 2016 as part of the first installment of ExoMars, a two-launch European-Russian partnership to the Red Planet. What is particularly strange about the detections, scientists say, is that they line up with where scientists would look for methane, a key component in the search for life on Mars. That unlikely alignment means that these compounds may interfere with scientists' attempts to look for methane.

"These features are both puzzling and surprising," Kevin Olsen, a planetary scientist at the University of Oxford and a researcher on the project, said in an ESA statement. "They lie over the exact wavelength range where we expected to see the strongest signs of methane."

Related: Photos: Europe's ExoMars missions to Mars in pictures

Scientists are fascinated by methane (or its absence) on Mars because, at least here on Earth, while geological processes produce a little of the gas, most of it comes from living things. That connection makes methane a potential biosignature, a marker that life could be nearby. The gas is also relatively short-lived, which means that if methane is spotted on Mars, it must have formed within the past few hundred years.

Researchers have tentatively identified methane on the Red Planet a few different times, including based on data gathered by NASA's Curiosity rover and by ESA's Mars Express orbiter. But those detections have been unclear and complicated, including frequent apparent mismatches between data gathered on the ground and observations from orbit.

This new detection of other gases, strangely aligned with where scientists typically look for methane, could help to explain why the question of methane in Mars' atmosphere has been so difficult to pin down, the scientists behind the new research said.

Carbon dioxide and ozone, alas, are both much more common on the Red Planet than methane, and scientists have seen both compounds plenty of times — carbon dioxide dominates the planet's thin atmosphere. But the Trace Gas Orbiter was able to measure them more precisely, thanks to an instrument called the Atmospheric Chemistry Suite that "tastes" the different components enveloping Mars.

While these compounds have been "sniffed out" on Mars before, these new observations are still intriguing, the scientists said. For example, the strange carbon dioxide signal, the researchers suspect, may point to a previously unknown interaction between the gas and other compounds in the atmosphere, or between the gas and sunlight.

And, while researchers typically study Martian ozone using ultraviolet measurements, the new detection was based on observations with infrared light. And, since ultraviolet measurements only work for ozone at higher altitudes, using infrared instruments could allow scientists to develop a much better understanding of how ozone is behaving low in the atmosphere, closer to the surface of Mars.

"Ozone and [carbon dioxide] are important in Mars' atmosphere," Alexander Trokhimovskiy, an engineer at the Space Research Institute of the Russian Academy of Sciences in Moscow and a researcher on the project, said in the same statement. "By not accounting for these gases properly, we run the risk of mischaracterizing the phenomena or properties we see."

The Trace Gas Orbiter, along with the failed Mars rover Schiaparelli, made up the 2016 launch of the ExoMars program, a partnership between ESA and Russia. The second launch in the program, which includes a rover dubbed Rosalind Franklin, was set to blast off this summer but was delayed to 2022 this spring because of parachute problems and complications from the coronavirus pandemic.

That mission will carry instruments similar to the Atmospheric Chemistry Suite on the Trace Gas Orbiter, allowing scientists to compare orbital data with measurements from the surface.

The research is described in two papers published in the July issue of Astronomy & Astrophysics.

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Meghan Bartels
Senior Writer

Meghan is a senior writer at and has more than five years' experience as a science journalist based in New York City. She joined in July 2018, with previous writing published in outlets including Newsweek and Audubon. Meghan earned an MA in science journalism from New York University and a BA in classics from Georgetown University, and in her free time she enjoys reading and visiting museums. Follow her on Twitter at @meghanbartels.