ESA’s ExoMars Trace Gas Orbiter has caught spikes of hydrogen chloride (HCl) above fresh fissures on the northern flanks of Alba Mons, a huge, low shield volcano, in early northern summer — exactly when this gas usually vanishes from Mars’s air. The orbiter’s CaSSIS camera shows narrow cracks, some hundreds of metres long, with discoloured ground around them. The team led by Alexander Trokhimovskiy and Daniel Mège (Polish Academy of Sciences) suggests winter ice at about −120 °C seals the cracks and that, as it vanishes in summer, gas from a still-warm magma body below escapes, like fumaroles on Earth (Science Advances, 4 Nov 2026). Caveat: no eruption or fresh lava has been seen; the volcanic origin is an interpretation that still has to be proved.
HClhydrogen chloride spikes in early summer
100s of mlength of the fresh fissures seen by CaSSIS
−120 °Cwinter ice that may seal the cracks