Enigmatic HCl detections as a potential signature of igneous activity on Mars.

Hydrogen chloride (HCl) is detected at part-per-billion levels in Mars’ atmosphere during the cold aphelion season, isolated to the Alba Mons region.

• Why it matters: Mars’ lack of ongoing volcanism is uncertain, and sulfur dioxide remains undetected; halogen gas seepage could better signal active magma.
• What they did: Using Atmospheric Chemistry Suite observations, the study reports HCl detections in the cold aphelion season and links them to fresh, narrow (<1 meter) fissures in Alba Mons.
• The result: The combined HCl detections and <1 meter fissures are best explained by ongoing igneous processes in the Martian interior, implying active subsurface pathways there.

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