Analysis of 2021 observations from the European‑Russian ExoMars Trace Gas Orbiter has revealed that Mars is releasing hydrogen chloride (HCl) gas from the vicinity of Alba Mons, the planet’s largest volcano by surface area. The discovery, reported in a paper published in Science Advances, points to possible recent volcanic activity beneath the Martian surface.
Hydrogen chloride emissions detected
Scientists have long recorded seasonal variations in HCl across the Red Planet, but the 2021 data showed spikes that appeared in unexpected locations and at unusual times. Those spikes were concentrated around the flanks of Alba Mons. Researchers interpret the emissions as a slow “belching” of hydrogen chloride, likely sourced from hot magma deep beneath the crust.
Fissures on Alba Mons indicate subsurface activity
The international team identified new fissures extending for thousands of feet around the volcano. Discolorations along these cracks suggest mineral deposits formed by seeping gases, a pattern comparable to volcanic gas vents on Earth. Co‑lead author Daniel Mège, a professor at the Polish Academy of Sciences, said the Trace Gas Orbiter acted like “a needle in a haystack,” detecting a handful of HCl molecules from a potentially intermittent source while continuously orbiting the planet.
“Our findings suggest that Mars has retained enough internal heat to support volcanic activity until recently, and possibly still does,” Mège stated. The presence of active fissures could provide pathways for gases to escape, creating the observed HCl signatures.
Implications for past habitability
Beyond the geological significance, the fissures may offer promising sites for the search for ancient life. Mège argued that hydrothermal systems associated with active or recent volcanism could supply both the chemical ingredients and energy required for microorganisms, while also shielding them from harsh surface conditions.
“Looking for martian life in the seeping fissures of the Alba Mons region would make a lot of sense,” he added. If Mars retained enough internal heat to drive volcanic outgassing, it may have once supported a warmer, thicker atmosphere capable of sustaining liquid water on the surface—a key factor in the planet’s habitability.
The findings add to a growing body of evidence that challenges the view of Mars as a completely geologically dead world. While the planet’s surface appears barren today, the detection of HCl emissions and the identification of fresh fissures suggest that the interior may still be dynamic, at least on a limited scale.
Future missions equipped to analyze the composition of these fissures directly could test the hypothesis of lingering volcanic activity and assess the potential for preserved biosignatures. For now, the Trace Gas Orbiter’s observations provide a compelling clue that Mars may have been geologically active much more recently than previously thought.
Helene Elliott is the Lead Science & Space Reporter at News Raise. She reports on aerospace missions, astrophysics discoveries, quantum research, and environmental technology.
