Mars Volcano Region Leaks Hydrogen Chloride, Hinting at a Hot Interior
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A European orbiter has detected traces of hydrogen chloride gas rising from cracked ground near Alba Mons, the largest volcano on Mars by surface area. According to a study in Science Advances, as reported by ScienceAlert, the researchers say the signals point to magma still active in the planet's interior.
The detections came from the European Space Agency's ExoMars Trace Gas Orbiter. The authors say a local volcanic source is the best explanation, though they also lay out two other possibilities that are not volcanic in the deep-interior sense.
The key numbers behind the Mars gas finding
- Parts per billion. The hydrogen chloride signals are extremely faint. ScienceAlert compared them to a single drop of ink in a 10,000-gallon swimming pool. Co-lead author Daniel Mège of the Space Research Centre of the Polish Academy of Sciences likened the search to finding a needle in a haystack.
- 3.7 to 3 billion years ago. This is the span of Mars' Hesperian era, when the planet was very volcanically active and later built the largest volcanoes in the Solar System, according to the report.
- Two million years ago. Olympus Mons may have shown recent activity around this time, ScienceAlert noted. Several regions of Mars also show signs of volcanic activity within the past tens of millions of years.
- -120 degrees Celsius (-184 degrees Fahrenheit). Cold snaps can plunge to this level and may freeze over cracks leading to the interior. Early summer warming in the northern hemisphere sublimates the overlying ice, which lets the gas escape.
- Tens of kilometers. Some of the small fissures linked to the gas form "swarms" that stretch this far, and some are ringed by dark halos, which the researchers say may resemble those around fumaroles on Earth.
How the researchers read the signals
Hydrogen chloride has been detected across Mars in different seasons, but many of those signals appear tied to the planet's water and atmospheric processes. A small number stand out. They appear in early northern summer, when Mars is near aphelion, its farthest point from the Sun.
That season is colder than the southern summer, and the air holds less dust and water vapor. ScienceAlert reported that this makes an atmospheric origin less likely and a magmatic one more likely. The signals also appear at lower altitudes. The detections sit above fissured ground near Alba Mons in the northern Tharsis Plateau, a region of recent and perhaps ongoing subsurface activity.
Hydrogen chloride is a useful clue because it keeps seeping from magma after eruptions end. Martian meteorites, rocks and regolith also show higher chlorine ratios than those on Earth. Other volcanic evidence, including heat signatures, surface features and sulfur-bearing gases, has been hard to find or inconclusive.
Three possible explanations
- The gas comes from deep volcanic sources.
- Mud volcanoes release it as they bubble up and interact with magma, which would still point to a volcanic source.
- Chlorine-containing compounds decompose at the surface.
The team favors a local igneous source. It argues that the fissures would have been buried by dust or reshaped by seasonal ground movement long ago unless something maintained them. They may be vents of hydrothermal systems linked to a deeper "volcanic plumbing system," the researchers suggest.
Why it matters for the search for Martian life
For general readers, the finding is a hint about the planet's present, not a confirmation. The study suggests Mars may not be geologically quiet, and that heat may still exist below its surface. That fits with other signs of an active planet, such as marsquakes and relatively recent lava flows, which ScienceAlert also mentioned.
Heat and chemistry could also matter for biology. Mège said that if hydrothermal systems are active, they could hold the ingredients and energy microorganisms need, and shelter them from the harsh surface. He said searching the seeping fissures of the Alba Mons region would make sense. Neither the study nor the report claims life has been found.
Read next
Mars Orbiter Spots Possible Volcanic Gas Leaks Near Giant Alba Mons
Gas Leaking From Mars Cracks Hints at Magma Still Moving Underground
Gas Seeping From Mars Fissures Suggests Its Volcanoes Are Dormant, Not Dead
Around Prague, based on reporting by ScienceAlert
