Mars Orbiter Finds Gas Leaks Hinting at Volcanoes Alive Today

"Looking at the spatial distribution of the seeping, it became instantly obvious to me that there was something volcanic behind it, but it had to be demonstrated," Mège explained. "We needed to be rigorous, critical, and creative to explain the presence of hydrogen chloride. The data were complex, but also excellent brain food."

The gas localization itself came from TGO's Atmospheric Chemistry Suite (ACS), a set of three infrared spectrometers — instruments that identify gases by the fingerprints they leave in light.

Why does the gas arrive in summer?

The timing points to a seasonal plug. During winter, temperatures around the fissures drop to -120 degrees Celsius, freezing the openings shut. Hydrogen chloride rising from below gets trapped, and the pressure builds until early summer, when the ice melts and sublimates — turns directly to vapor — and the gas escapes in a burst.

The team's analysis links the emissions to a dormant magma chamber beneath Alba Mons, a kind of "volcanic plumbing system" that still channels gases toward the surface. The gas release happens just after winter frost disappears.

That's the mechanism. But no eruption has ever been observed, so the claim of present-day volcanism stays hedged for now.

Is Mars really still active?

The question has been open for years. Mars hosts the largest volcanoes in the solar system; Alba Mons alone, the biggest by surface area, rises 6.8 km at its peak, and some deposits around it are over three billion years old. Orbiter imagery suggests some volcanoes were active as recently as a few million years ago, and NASA's InSight lander recorded thousands of "marsquakes."

Yet nobody has seen an eruption. The hydrogen chloride fissures are the strongest atmospheric hint so far that the planet's interior still holds heat.

Mège credits the orbiter for catching it: "The Trace Gas Orbiter was able to find the smoking gun. It was like looking for a needle in a haystack. It's truly amazing that it spotted a handful of molecules from a perhaps intermittent source, whilst moving continuously along its orbit to monitor the whole Martian atmosphere."

Why habitability matters here

The findings carry more than geological weight. Millions of years ago, hydrogen chloride and other magmatic gases helped build a thick, warm Martian atmosphere — conditions under which liquid water flowed. If the fissures ever allow magma to reach groundwater, they could create small pockets of habitable conditions.

"Looking for Martian life in the seeping fissures of the Alba Mons region would make a lot of sense," Mège said. Active hydrothermal systems could supply the ingredients and energy microorganisms need, while shielding them from the harsh surface environment.

TGO launched on a Proton rocket from Kazakhstan in March 2016 and entered a 400-by-400-km circular orbit around Mars that October. It was built to study methane and other trace gases, and it has now shown it can flag potentially habitable regions just by sniffing the air. "These findings may prove to be TGO's greatest success yet," said ESA project scientist Colin Wilson.

The caveats are real: the evidence is indirect, and a dormant magma chamber is an interpretation, not a confirmed observation. But for now, the gas keeps leaking on schedule each Martian summer.