Gas Leaking From Mars Cracks Hints at Magma Still Moving Underground

A spacecraft orbiting Mars has detected a noxious gas, hydrogen chloride, rising above fresh cracks in the ground near the giant volcano Alba Mons. An international team says this may be some of the strongest evidence yet that magma still moves beneath the Martian surface, EarthSky reported.

The researchers announced the result on Nov. 4, 2026, in a peer-reviewed paper in Science Advances. The volcanoes themselves are not erupting, and the finding does not show that they are. The team argues that the gas is best explained by ongoing igneous activity deep inside the planet.

What the orbiter found near Alba Mons

The detections came from the European Space Agency's Trace Gas Orbiter. According to EarthSky, the gas appeared at parts-per-billion levels, which is tiny but higher than expected. Alba Mons lies northeast of Olympus Mons, the largest volcano in the solar system.

The gas was seen above geologically fresh cracks around the volcano. EarthSky reported that the cracks are several hundred meters long and tens of centimeters wide. The paper describes them as narrow fissures, less than 1 meter across, that could act as pathways connected to magma bodies at depth.

Why the timing of the detection matters

Hydrogen chloride is already known to be widespread in the Martian atmosphere, but mostly in warmer seasons, when it behaves as an aerosol. Aerosols are fine solid particles or liquid droplets suspended in the air. Earlier observations by another instrument, the Atmospheric Chemistry Suite, found the gas at parts-per-billion levels during the warm period when Mars is closest to the sun.

In the cold season, when Mars is farthest from the sun, the gas normally largely vanishes from view because water ice crystals absorb its molecules. The new detections came during that cold season, were isolated to the Alba Mons region and occurred at low altitudes. The authors say the observed atmospheric conditions and models do not explain them. Together with the local geology, they point to a source in the planet's interior.

On Earth, moving magma often releases hydrogen chloride, though it is a minor volcanic gas there compared with water vapor, carbon dioxide and sulfur dioxide. EarthSky noted that scientists think hydrogen chloride could be a major volcanic gas on Mars.

What is still uncertain

The researchers do not claim the gas comes straight from magma. It might instead come from a buffer zone, a layer of permafrost above the magma. In that scenario, ice traps the gas in winter, and as temperatures rise in spring the ice sublimates and releases it into the atmosphere.

EarthSky also noted that the gas levels, though higher than expected, still depend on future studies confirming that the gas is there at all. Sulfur dioxide, which could signal eruptions, has so far not been detected on Mars. The paper says evidence of active magma chambers may be easier to spot through seepage of halogen gases such as hydrogen chloride.

What this means for our picture of Mars

The result has no direct effect on daily life, but it bears on how scientists understand Mars. The planet has no moving tectonic plates to keep reshaping its surface, so it has long been viewed as largely dormant. That view has been shifting. NASA's InSight lander detected more than 1,300 seismic events, showing that marsquakes still occur, and evidence of relatively recent volcanic activity has been building.

Co-lead author Daniel Mège of the Space Research Center of the Polish Academy of Sciences said the findings suggest Mars kept enough internal heat to support volcanic activity until recently, and possibly still does. He described the orbiter's detection as finding the "smoking gun," and said it was remarkable that the instrument caught a handful of molecules from a possibly intermittent source while moving along its orbit.

Mège also said much of the work went into examining every chemical process that could be at play in the Martian atmosphere, to explain the hydrogen chloride without invoking volcanism. The team concluded that an underground igneous source fits best.

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Around Prague, based on reporting by EarthSky