Overview
- The Science Advances study published Wednesday reports repeated, spatially confined detections of chlorhydric acid (HCl) above the flank of Alba Mons by the ExoMars Trace Gas Orbiter's Atmospheric Chemistry Suite.
- The HCl appeared in early northern summer when the gas is usually scarce, a seasonal pattern that the authors say is hard to reconcile with previously proposed dust–water atmospheric chemistry.
- High-resolution CaSSIS and other imagery show narrow, sometimes several-hundred-metre-long fissures at the sites and nearby light or dark discolorations that could be deposits from escaping gases.
- Study authors propose the signals could come from gases rising along fissures from a still-warm magmatic body but emphasize that HCl alone is not direct proof of active volcanism and that non‑volcanic chemical pathways remain viable explanations.
- If a warm magmatic source is confirmed it could create local hydrothermal niches of astrobiological interest, and the team calls for follow-up orbital measurements and analyses to seek direct evidence of subsurface heat or fluids.