ExoMars TGO detects hydrogen chloride over Mars's Alba Mons volcano; authors link it to magma
Spectrometers on the ExoMars orbiter found localized HCl above Alba Mons in the cold season. The authors link it to ongoing igneous processes in the Martian interior.
A team led by Alexander Trokhimovskiy reported detections of hydrogen chloride (HCl) in the Martian atmosphere during the cold aphelion season, isolated in the Alba Mons region. The study, published on 4 November 2026 in Science Advances, uses data from the Atmospheric Chemistry Suite on the ExoMars Trace Gas Orbiter science.org
Science Advancesscience.orgOpen source ↗. The authors conclude that the results are best explained by ongoing igneous processes in the Martian interior.
HCl signal above Alba Mons
Earlier observations by the Atmospheric Chemistry Suite found HCl at part-per-billion levels across the Martian atmosphere during the warm perihelion period. That widespread signal was attributed to aerosol-atmospheric sources. The new detections differ: they are localized above volcanic fissures on the flanks of Alba Mons and recur in the same place in early northern summer, just after winter frosts sublimate.
Sulfur dioxide, which could also indicate eruptive activity, has so far not been detected on Mars. According to the authors, seepage of halogen gases such as HCl may identify active magma chambers better. Marsquakes have been recorded recently, and clues to volcanism younger than tens of millions of years have accumulated. No new lava flows or eruptions have been observed.
Fresh fissures and the magma scenario
Images from the orbiter's CaSSIS camera show fresh, narrow fissures in the area, under 1 meter wide. Some are hundreds of meters long and are associated with changes in surface color science.org
Science Advancesscience.orgOpen source ↗. The authors interpret them as possible pathways for HCl rooted in magmatic bodies at depth.
The team proposes that a dormant magma chamber supplies gases that rise through the fissures. In winter, with temperatures down to −120°C (−184°F), ice could block the openings. As it sublimates in early summer, the gases would reach the atmosphere, much as at fumaroles on Earth. Deposits left by the escaping gases could also explain the discoloration around the fissures.
Daniel Mège of the Space Research Centre of the Polish Academy of Sciences, a co-lead author, said the findings suggest Mars retained enough internal heat to support volcanic activity until recently, and possibly still does. He added that if hydrothermal systems are active there, they could contain the ingredients and energy needed for microorganisms. This remains a hypothesis: the gas source itself has not been observed directly.
