ExoMars orbiter finds hydrogen chloride spikes over Alba Mons, hinting at magma still warm under Mars

5 November 2026

Europe's ExoMars Trace Gas Orbiter has detected unexpected spikes of hydrogen chloride in the Martian atmosphere above volcanic fissures on the flanks of Alba Mons.
The gas was picked up by the orbiter's Atmospheric Chemistry Suite of infrared spectrometers, appearing in early northern summer and outside the usual seasonal pattern, while the orbiter's CaSSIS camera imaged fresh narrow fissures, some hundreds of metres long, next to colour changes on the ground.
The international research team, led by Alexander Trokhimovskiy, suggests the chlorine is carried up from hot magma below, a sign of volcanism that is dormant rather than dead.
The fissures may channel the gas out as surface ice sublimates at temperatures as low as minus 120 degrees Celsius.
The paper, titled Enigmatic HCl detections as a potential signature of igneous activity on Mars, appeared in Science Advances on 4 November 2026.
The orbiter first reported hydrogen chloride on Mars in 2021.
Mars carries the largest volcanoes in the Solar System, but no eruption or new lava flow has ever been observed there.