New evidence from gas seeping above volcanic rifts suggests Mars is not geologically dead deep inside, but merely sleeping.
Fresh fissures along the Alba Mons region hint at active spots under the surface, where gases from inside the planet may be making their way up to the surface.
An international research team led by Alexander Trokhimovskiy suggests that the release of hydrogen chloride comes from hot magma beneath the surface – a sign of dormant volcanism.
The ExoMars Trace Gas Orbiter (TGO) first reported hydrogen chloride gas in the martian atmosphere back in 2021. This gas is commonly found escaping from magmatic vents on Earth, leading researchers to wonder whether the same was happening on Mars.
"Our findings suggest that Mars has retained enough internal heat to support volcanic activity until recently, and possibly still does," says Daniel Mège , Professor at the Space Research Centre of the Polish Academy of Sciences and co-lead author of a paper published in Science Advances yesterday.
Rising gas
It was early summer in the northern hemisphere of Mars when a team of researchers noticed spikes of hydrogen chloride where it shouldn't have been, and during an odd season.
This gas varies seasonally on Mars, reaching its maximum in northern hemisphere winter, then mostly disappearing in the summer. Most of this variability appears to be linked with Mars' dust and water cycles . Yet there was one exception to this pattern, always in the same season and at the same place – above volcanic fissures on the flanks of the Alba Mons volcano, in early summer.
Mars is not dead, just dormant
Mars has the largest volcanoes in the Solar System, but it is not known how active they are. Orbital imagery shows that some volcanoes appear to have been active within the last few million years , and seismometers have detected marsquakes – the earthquakes of Mars. Both facts point to the possibility of Mars being volcanically active.
However, no new lava flows or eruptions have ever been observed.
Fissures and seasonal gases
The finding is the result of combined atmospheric and geological analysis. First came the detection of hydrogen chloride strongly localised in space and at a time just after the frosts of winter sublimate. The infrared spectrometers from TGO's Atmospheric Chemistry Suite were on the case.
Then a close look at the Alba Mons region using TGO's CaSSIS camera showed fresh and narrow fissures, in some cases hundreds of metres long, associated with colour changes on the surface.
"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," explains Daniel.
Scientists suggest magmatic gases might be rising through these fissures, like some fumaroles on Earth. Blocked by ice during winter's freezing temperatures, down to -120°C, the fissures would channel the release of chloride as the ice sublimates in early summer.
The discolouration around the fissures could come from deposits left behind by gases escaping from Mars's interior, as around fumaroles (volcanic gas vents) on Earth.
The team of researchers relied on geological intuition to make the link between the gas and the rifts. "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" concedes Daniel.
"A huge part of the work consisted of examining all the possible chemical processes going on in the martian atmosphere. We needed to be rigorous, critical and creative to explain the presence of hydrogen chloride. The data were complex, but also excellent brain food," adds Daniel.
The team suggests that the seepage is connected to a dormant magma chamber, a sort of volcanic plumbing system under the martian surface.
Niches for life
Magmatic gases like hydrogen chloride could have been more abundant in the past, contributing to a thicker atmosphere and warmer climate and allowing liquid water to cover much of the martian surface. If lava rising through the crust meets groundwater, this could lead to warm habitable niches.
"Looking for martian life in the seeping fissures of the Alba Mons region would make a lot of sense. If hydrothermal systems are active, they could contain the ingredients and energy needed for microorganisms to develop, and shield microorganisms from the hostile and changing environment above the surface," ponders Daniel.
"These findings may prove to be TGO's greatest success yet," highlights Colin Wilson, ESA's project scientist for the ExoMars Trace Gas Orbiter.
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Paper published in Science Advances on 4 November 2026, 'Enigmatic HCl detections as a potential signature of igneous activity on Mars'
