PARIS, Friday, November 6, 2026 — A European orbiter circling Mars has detected traces of hydrogen chloride gas rising from cracks on the flanks of the planet's largest volcano, Alba Mons, in what scientists say may be the strongest hint yet that Mars is not entirely geologically dead. The gas appeared again and again above the same narrow fissures, in a season when the usual explanation for it does not apply, suggesting that heat from a dormant volcanic system deep below the surface could still be seeping upward.
Illustration: The ExoMars Trace Gas Orbiter above Mars, with the broad shield volcano Alba Mons below.
What Happened
The European Space Agency (ESA) announced on Thursday, November 5, 2026, that its ExoMars Trace Gas Orbiter (TGO) had detected hydrogen chloride, known as HCl, above fissures on the flanks of Alba Mons, in the Tharsis region of Mars. The findings were published in the journal Science Advances on Wednesday, November 4, 2026, in a paper titled "Enigmatic HCl detections as a potential signature of igneous activity on Mars". The lead author is Alexander Trokhimovskiy of the Space Research Institute in Russia, and the co-lead author is Daniel Mège of the Space Research Centre of the Polish Academy of Sciences.
The detections were made by the orbiter's Atmospheric Chemistry Suite, or ACS, a set of infrared spectrometers that analyse the chemical makeup of the Martian atmosphere. The gas was found in early northern summer on Mars, at a concentration of about two parts per billion by volume, according to Mège.
What makes the findings unusual is where and when the gas appeared. The detections were strongly localised in both place and time: they occurred repeatedly above the same fissures on Alba Mons, and they happened in the aphelion season, the part of the Martian year when the planet is farthest from the Sun and dust storms are rare. Hydrogen chloride in the Martian atmosphere has previously been linked to dust storms, which can lift chlorine-bearing dust into the air. These new detections break that pattern, the researchers say, because there were no dust storms to explain them and the gas kept appearing over one specific place.
A second instrument on the orbiter added a visual clue. The Colour and Stereo Surface Imaging System, known as CaSSIS, photographed the area and showed fresh, narrow fissures on the volcano's flanks, some of them hundreds of metres long, with changes in the colour of the surface around them. The gas detections sit directly above them.
The researchers are careful about what that something might be. Their interpretation, presented as a hypothesis rather than a proven fact, is that the gas could be seeping from a dormant magma chamber, a reservoir of molten rock held in a volcanic plumbing system beneath the surface. No eruption has been observed, and no lava has been seen. The gas is a hint, not proof of an eruption, and the authors do not claim otherwise. What they argue is that the pattern of the detections is difficult to explain in any other way that fits the evidence so far.
"Our findings suggest that Mars has retained enough internal heat to support volcanic activity until recently, and possibly still does," Mège said. ESA's project scientist for the Trace Gas Orbiter, Colin Wilson, described the result in strong terms, saying the findings "may prove to be TGO's greatest success yet."
Background
Alba Mons is the largest volcano on Mars by surface area. It rises to about 6.8 kilometres in elevation and sits in the Tharsis region, north of Olympus Mons. Some of the deposits around Alba Mons are more than three billion years old, which is why the volcano has generally been regarded as an ancient, long-quiet giant. The new findings complicate that picture: a volcano that built its great bulk billions of years ago may still have a warm interior today.
The Trace Gas Orbiter itself has been at Mars for a decade. It launched in March 2016 and entered orbit around Mars in October 2016, as part of the joint ESA-Roscosmos ExoMars programme. Its main task has been to study the gases in the Martian atmosphere in fine detail. Hydrogen chloride was one of its early successes: the gas was first detected in the Martian atmosphere by the orbiter in 2021, in work led by Kevin Olsen. At that time, the detections were associated with dust storms.
That earlier explanation is exactly what the new work challenges. Dust storms can spread the gas widely and briefly, in step with the dusty season. The Alba Mons detections behave differently. They are pinned to one location, they repeat above the same fissures, and they occur in early northern summer, around aphelion, when dust storms are rare. A dust-driven explanation would predict the opposite: a broad signal, tied to stormy weather. The researchers therefore looked for a source that stays in one place and releases gas steadily, and a volcanic system beneath the fissures fits that description.
The fissures themselves are part of the evidence. Fresh cracks can act as pathways, letting gas escape from below to the atmosphere above. If a magma chamber or a warm volcanic plumbing system sits beneath Alba Mons, gas could travel upward through such fractures and emerge at the surface, where the orbiter's spectrometers can detect it. The picture is consistent, but it is still indirect: nobody has seen the chamber, and nobody has seen an eruption. The gas is the messenger, and the researchers are reading its message with care.
The paper's title carries the same caution: the detections are called "enigmatic", and the volcanic interpretation a "potential signature" of igneous activity, not a settled fact.
The result also sits apart from two other well-known Mars stories, and it should not be confused with either of them. The Rosalind Franklin rover, the next ExoMars rover, is planned for launch in 2028 and will target Oxia Planum, a different site entirely, to search for signs of past life. And the marsquakes recorded by NASA's InSight lander came from Cerberus Fossae and the Elysium Planitia region, a different part of the planet.
Illustration: Narrow fissures on the flank of Alba Mons, with faint gas rising from the cracks — the site of the new hydrogen chloride detections.
Why It Matters
The first reason this matters is the question it answers about Mars itself. Whether a planet is geologically alive or dead shapes almost everything scientists want to know about it: how its interior cools, how its atmosphere evolved, and whether conditions underground could have supported life, now or in the past. A Mars that still has warm, gas-releasing volcanic systems is a different world from a Mars that froze solid billions of years ago. It means the planet's interior is still doing something, visible only as a whisper of gas in the atmosphere.
The second reason is the method. The discovery was made from orbit, by watching the atmosphere, not by landing on the surface or drilling into the ground. That shows an orbiter with sensitive spectrometers can detect geological activity that leaves almost no visible trace, by reading the faint chemical signals that leak into the sky. If the technique works at Alba Mons, it can be applied elsewhere on Mars, turning the atmosphere into a diagnostic tool for what is happening deep underground. Future missions could be designed to watch for such signals deliberately, rather than stumbling across them.
The third reason is the connection to the search for life. Volcanic heat and the gases that come with it can create environments where liquid water might persist underground, and where chemical energy might be available to living things. Nobody is claiming that life exists beneath Alba Mons, and the new paper makes no such claim. But on Earth, volcanic systems are among the places where life thrives in extreme conditions, and a warm, gas-releasing system on Mars would be exactly the kind of place scientists would want to look more closely.
Illustration: A dormant magma chamber deep beneath Alba Mons, with volcanic plumbing rising toward the surface fissures.
What Happens Next
The most immediate next step is more observation. The Trace Gas Orbiter is still operating at Mars, and its instruments can keep watching the Alba Mons fissures to see whether the hydrogen chloride signal repeats in future early summers, whether it grows stronger or fades, and whether it appears at other times of the Martian year. A repeating signal would strengthen the volcanic interpretation considerably; a signal that vanishes would force scientists to reconsider. Either outcome would be useful, because both would narrow down what is happening below the surface.
Researchers will also want to look at the fissures themselves in greater detail. Further imaging could reveal whether the cracks are changing over time, whether new ones are opening, and whether the surface around them continues to evolve. Changes on the surface would be another line of evidence pointing to activity below, and they could be tracked from orbit without sending a lander.
Other missions may be able to help as well. Orbiters that have studied Mars for years carry their own spectrometers and cameras, and their archives may hold observations of Alba Mons that were not examined with this question in mind. In the longer term, the finding could influence where future missions look.
For now, the honest summary is the one the researchers themselves offer. Mars has given scientists a hint, not a verdict. A faint trace of hydrogen chloride, found above the same cracks again and again, in a season when it should not be there, suggests that the planet has retained enough internal heat to support volcanic activity until recently, and possibly still does. The orbiter will keep watching, and the gas will keep telling its story, a few parts per billion at a time.
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FAQ
What did the ExoMars Trace Gas Orbiter detect on Mars?
The orbiter detected hydrogen chloride (HCl) gas above fissures on the flanks of Alba Mons, the largest volcano on Mars by surface area. The gas was found at about two parts per billion by volume, in early northern summer, using the Atmospheric Chemistry Suite infrared spectrometers. The detections repeated above the same fissures.
Why do scientists think this gas could come from a volcano?
Hydrogen chloride in the Martian atmosphere has previously been linked to dust storms, but these detections break that pattern: they happened in the aphelion season, when dust storms are rare, and they stayed pinned to one location. The CaSSIS camera also showed fresh, narrow fissures with surface colour changes around them. The researchers' interpretation is that the gas may be seeping from a dormant magma chamber beneath the surface. That interpretation is a hypothesis, not proof.
Has an eruption been observed on Mars?
No. No eruption and no lava have been observed. The finding is a hint of possible volcanic activity, based on a faint gas signal and the fissures above which it appears. Daniel Mège said the findings suggest Mars has retained enough internal heat to support volcanic activity until recently, "and possibly still does", but further observation is needed before any stronger claim can be made.
What is Alba Mons?
Alba Mons is the largest volcano on Mars by surface area. It rises to about 6.8 kilometres in elevation and sits in the Tharsis region, north of Olympus Mons. Some of the deposits around it are more than three billion years old, which is why it has long been regarded as an ancient, quiet volcano.
What happens next in this research?
The Trace Gas Orbiter, which launched in March 2016 and has been in orbit at Mars since October 2016, will keep watching the Alba Mons fissures to see whether the hydrogen chloride signal repeats in future early summers. Researchers will also study the fissures in greater detail and may re-examine older observations from other orbiters.
Sources
- "European orbiter detects fresh hints of volcanic activity on Mars," phys.org, November 4, 2026. https://phys.org/news/2026-11-european-orbiter-fresh-hints-volcanic.html
- "European orbiter detects hints of volcanic activity on Mars," Oxford Physics, November 2026. https://www.physics.ox.ac.uk/news/european-orbiter-detects-hints-volcanic-activity-mars
- "ExoMars TGO finds evidence of volcanic activity on Mars," NASASpaceflight, November 4, 2026. https://www.nasaspaceflight.com/2026/11/tgo-volcanic-activity/
- "European orbiter detects hints of volcanic activity on Mars," Space and Defense, November 2026. https://spaceanddefense.io/european-orbiter-detects-hints-of-volcanic-activity-on-mars/
- "Mars's Largest Volcano Leaking Volcanic Gas? New Detection Method Found What Thermal Surveys Missed," Tech Times, November 5, 2026. https://www.techtimes.com/articles/330081/20261105/marss-largest-volcano-leaking-volcanic-gas-new-detection-method-found-what-thermal-surveys.htm
- Alexander Trokhimovskiy et al., "Enigmatic HCl detections as a potential signature of igneous activity on Mars," Science Advances, November 4, 2026. DOI: 10.1126/sciadv.aeb9422. https://www.science.org/doi/10.1126/sciadv.aeb9422
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