A noxious gas seeping through cracks on Mars may be a sign of magma beneath the surface, and perhaps of an environment a bit like the hydrothermal vents where life likely arose on Earth, Live Science reported. Europe's ExoMars Trace Gas Orbiter spotted a possible signal of hydrogen chloride leaking from rifts in the region of Alba Mons, the largest volcano on Mars by surface area, though Olympus Mons is taller. Scientists interpret the gas as emissions from hot magma below the regolith. The study, published Nov. 4 in Science Advances, "is not the first to suggest that magma may be flowing on Mars," Live Science noted; NASA's InSight lander had interpreted its presence through seismic observations earlier this year. But the new findings are "the strongest evidence yet of gases being released by dormant volcanoes on Mars," first author Alexander Trokhimovskiy, of Russia's Space Research Institute, told the site. "Our study offers a complementary and potentially independent line of evidence [of Martian magma]: Atmospheric observations that reveal a possible signature of gas release from a subsurface magmatic system."
TGO first detected hydrogen chloride in Mars's atmosphere in 2021, but scientists were hesitant to link it to volcanoes. The gas appeared seasonal, was not localized at a volcanic region, and other volcanic gases, such as sulfur, were not present, co-author Kevin Olsen, a visiting researcher at the University of Oxford, told Live Science. Later work suggested it was not confined to southern spring and summer; it also appeared in northern winter. "I managed to catch two observations from the start of northern winter in the first Mars year of our mission, and a single observation the next year," Olsen said. A year on Mars is closer to two years on Earth. Those out-of-season measurements were close to one another in location and time in both years, which he called surprising. The team then ran a targeted campaign for two Mars years, about four Earth years.
They confirmed a "distinct and pronounced signal" in the northern hemisphere that then diminished and fell below the spacecraft's detection threshold. "This inconsistency is more suggestive of a puff of gas entering the atmosphere than of regular atmospheric chemistry," Olsen said. "While the link remains a hypothesis, we have now seen this gas appear locally, and nowhere else, over four Mars years of observations." Co-author Daniel Mège, a planetary geologist at the Polish Academy of Sciences, identified the fissures where the gas may be emerging. He said InSight's ground data and TGO's atmospheric detections complement each other.
Magma activity is not itself a sign of life. Mège noted that Earth's first life-forms came from sites like hydrothermal zones, which have a similar mix of materials and energy. But conditions would need to stay favorable for at least millions of years. "If these requirements are met at local scale, at the scale of the seepage structures, then living organisms might wait for us to discover them," he said. "But maintaining stable conditions over such a long period at a very local scale is not obvious." The verified claim is a localized, repeating hydrogen-chloride signal near Alba Mons, still described by the authors as a hypothesis, not a confirmed inhabited vent.