Exomars Data Suggests Active Magmatic System Near Alba Mons on Mars

Alba Mons Flanks Reveal 1.5 Parts per Billion Hydrogen Chloride Spike

Orbiting instruments above Mars have detected trace amounts of hydrogen chloride peaking at up to 1.5 parts per billion above the flanks of the shield volcano Alba Mons, according to data published in Science Advances.

Now, measurements gathered by the ExoMars Trace Gas Orbiter point toward an active magmatic system beneath the Martian surface, suggesting underground heat and gas release may still occur.

The detected gas appears during the northern hemisphere’s early summer. At this time of year, hydrogen chloride vanishes across almost the rest of the planet.

Orbital Cameras Capture Fresh, Narrow Cracks Below Venting Sites

Below the detection points, orbital cameras reveal swarms of fresh, narrow cracks measuring less than a meter in width. These previously unmapped fissures stretch across the northern flank of the volcanic structure.

Alexander Trokhimovskiy of the University of Bern led the international research team analyzing the orbiter data. The team combined imagery from the CaSSIS color camera with high-resolution views from NASA's Mars Reconnaissance Orbiter to scan the terrain.

The CaSSIS camera on board the ExoMars Trace Gas Orbiter captured this roughly 20 by 20 kilometer region on the northern flank of the Martian volcano Alba Mons on February 3, 2023. Special colored deposits around the fissures serve as an additional clue.

Testing Alternative Chemical Processes Behind Spurengase History

Mège described the volcanic interpretation as an initial intuition that required rigorous testing. As I looked at the spatial distribution of the venting, I immediately realized that something volcanic was behind it – but it had to be proven, he explained.

Most of the team’s effort focused on testing and ruling out alternative chemical processes in the atmosphere that might have generated the gas. Spurengase on Mars carry a debated history within planetary science. Mineral dust was treated as a source in climate models, while ice particles took up hydrogen chloride from the air and thereby shortened its lifetime.

Ice-Rich Ground Acts as a Seasonal Chlorine Valve

A larger seasonal pulse of chlorine circulates globally near the planet’s closest approach to the sun at roughly 180 kilograms per second. Researchers do not consider this broad atmospheric cycle to be volcanic in origin, though some ancient chlorine likely originated from the interior.

Ice-rich ground in the region may act as a seasonal valve between a deeper gas source and the atmosphere. Frozen material can trap hydrogen chloride during the local winter before releasing it as temperatures rise, with increasing warmth in the spring turning ice directly into water vapor.

A Dormant Rather Than Extinct World

No active volcanic eruption has ever been observed on the planet. The localized gas signatures and fresh fissures indicate the world may be dormant rather than completely extinct.