To understand the significance of what is happening on Mars right now, you first have to appreciate how long we have believed the planet to be dead. For most of human space exploration, Mars has been categorized as a dormant world, a frozen relic where the last active volcanoes died out millions of years ago. This reputation as a geologically inactive planet shaped every mission sent to the red dust. It meant we weren't really looking for fresh signs of life, because the engine that drives geological and, potentially, biological activity was thought to be off. But that assumption is now under serious challenge by a discovery that feels almost like a ghost story: the detection of a gas that should not be there if the planet’s interior were truly cold and static.
The signal was first picked up in 2021 by the ACS complex, a sophisticated spectrometer part of the ExoMars-2016 Trace Gas Orbiter mission. Researchers from the Space Research Institute (IKI) of the Russian Academy of Sciences were analyzing atmospheric data when they noticed a trace of hydrogen chloride. The concentration was minute—on the order of billionths—which is why it had escaped detection for so long. It was not a massive eruption or a visible plume; it was a chemical fingerprint, a subtle anomaly that suggested something was leaking from the subsurface. The detection marked the first time hydrogen chloride had been registered in this context, opening a window into processes that were previously hidden from view.
Mars may not be geologically dead after all. 🔴 Our ExoMars Trace Gas Orbiter has detected hydrogen chloride above volcanic fissures in the Alba Mons region, which scientists suggest could be linked to dormant volcanic activity beneath the surface. Read more: https://t.co/VEJRtcff8V
What makes this gas behave so oddly is its relationship with the Martian seasons. The data shows that hydrogen chloride is not constant. It peaks during the winter of the northern hemisphere and then almost disappears entirely in the summer. This seasonal ebb and flow is crucial. It suggests a mechanism involving permafrost. Scientists hypothesize that hydrogen chloride is trapped in the frozen ground during the colder months and is released seasonally as the temperature shifts. This gas was specifically detected during the cold aphelion season, a time when the planet is farthest from the sun and the atmospheric conditions are extreme. This cyclical release is not just a weather pattern; it is the respiratory rhythm of a planet that is still exchanging gases with its interior.
Researchers from the University of Bern and the European Space Agency independently analyzed data from the Trace Gas Orbiter.
The correlation between the gas and a specific location is what moves this from interesting to potentially revolutionary. The distribution of the hydrogen chloride tracks the region of Alba Mons, a massive shield volcano. On Earth, we know that shield volcanoes are fed by broad, shallow magma chambers. The presence of the gas in this area, combined with observations of narrow cracks on the surface, points to a subsurface magmatic source. These fissures suggest that the crust is not just cracking from cooling, but is being pushed apart or released from pressure coming from below. It is as if the planet is holding its breath, and these cracks are the places where it leaks out.
Photo from ESA showing the Acheron Fossae region on Mars, located between two giant volcanoes—Olympus Mons to the south and Alba Mons to the northeast. This area is rich in geological features, such as grabens (trough-like depressions formed by tectonic activity) and rock glaciers.(ESA)
This interpretation is not the work of a single lab. Researchers from the University of Bern and the European Space Agency independently analyzed data from the Trace Gas Orbiter. Their findings reinforced the initial detection, identifying the same presence of hydrogen chloride and linking it to the physical evidence of fissures. This convergence of data from different institutions and different analytical approaches strengthens the claim. It suggests that the signal is not an instrument error but a real feature of the Martian atmosphere. The combined analysis challenges the traditional view of Mars as a static, dead rock, replacing it with a picture of a world where geological processes are still active, however slowly.
The core hypothesis proposed by the scientists is that the hydrogen chloride is a tracer for magma. In a volcanic system, gases are released from the melt as it rises. If there is a source of hydrogen chloride correlating with a known volcanic structure, and if that gas is behaving in a way consistent with seasonal release from the subsurface, it implies that there is still magmatic material moving beneath the crust. This is not proof of an imminent eruption, but it is proof that the engine is not off. It is idle, perhaps, but it is not broken. It is ticking over, cycling elements from the deep interior up toward the surface and atmosphere.
Mars may still be volcanically active. Scientists detected hydrogen chloride gas above fissures near Alba Mons, a vast Martian volcano. They think it may be seeping from underground magma; if so, that heat could also create conditions worth exploring in the search for microbial life. Mars may look quiet from here, but apparently it hasn’t finished with us. https://t.co/siVNzMnq2N
Alexander Trokhimovsky, a researcher associated with the findings, put the stakes plainly. He noted that they seem to have managed to find, for the first time, a very serious proof of active magmatic activity on Mars not in the past, but right now. This is a profound shift. It reopens the question of habitability. A planet with an active geological engine is a planet with a dynamic environment. It is a planet that cycles carbon, water, and heat. These are the ingredients that can support complex chemistry and, potentially, life. The discovery of these new signs of volcanic activity rekindles hopes that we have not been looking in the right places for the right reasons.
Today, we stand at a crossroads in planetary science. The data from the ExoMars mission and the Trace Gas Orbiter suggests that Mars is not a museum piece. It is a living system, albeit a slow one, that still communicates with its surface through the release of gases like hydrogen chloride. The narrow cracks and the seasonal variations in the atmosphere are the new facts that must be explained. They tell us that the story of Mars is not finished. It is still being written, one quiet chemical release at a time, deep below the shield volcanoes where the heat has not yet faded.