Europe’s ExoMars Trace Gas Orbiter has handed planetary science a quiet but striking clue: Mars may still leak volcanic gas. A Science Advances study led by Alexander Trokhimovskiy reports unusual hydrogen chloride (HCl) pulses above the northern flank of Alba Mons — sharp, localised, and out of step with the dust-and-ice chemistry that usually explains HCl in the southern summer.
Amounts are tiny, around two parts per billion, yet they sit over fresh fissures roughly a hundred metres long that geologists link to vertical magma sheets. Polish Academy of Sciences researcher Daniel Mège says the clues “point to a volcanic origin.” Ice seal in winter; when northern summer arrives, the gas can seep out.
Caveats remain loud. The team cannot prove those exact cracks are the vents, and Oxford physicist Kevin Olsen stresses the source could be trapped gas pockets or hydrothermal chemistry instead of molten rock. No lava rivers have been caught on camera — this is passive degassing above what may be a still-warm magmatic system, not an erupting plume.
Even so, dormant volcanism would rewrite textbooks that call Mars geologically dead and keep alive the idea that subsurface heat and fluids could shelter microbes. The orbiter’s Atmospheric Chemistry Suite did not deliver fireworks; it delivered a scent. Follow-up orbits and sharper imaging of Alba Mons will decide whether the Red Planet is merely sleeping.
Alba Mons is Mars’s most sprawling volcano; youthful lava sheets and earlier InSight marsquakes elsewhere already hinted that something under the crust may still stir.
