Scientists say they've uncovered evidence of volcanic activity on Mars.
The evidence, captured by the European Space Agency's ExoMars Trace Gas Orbiter, suggests Mars isn't geologically dead below its surface, but is merely sleeping.
Images show fissures along a region on Mars known as Alba Mons indicate potential active spots under the planet, where gases from inside Mars are making their way up to the surface.
"Our findings suggest that Mars has retained enough internal heat to support volcanic activity until recently and possibly still does," says Daniel Mège, Professor at the Space Research Centre of the Polish Academy of Sciences and co-lead author of the science paper.
More on Mars
Spotting rising gas on Mars
An international team of scientists led by Alexander Trokhimovskiy made the discovery, which shows evidence of hydrogen chloride being released by hot magma under the surface of Mars.
That could be a sign of dormant volcanism.
The ExoMars Trace Gas Orbiter discovered hydrogen chloride gas in the Martian atmosphere back in 2021.
Scientists say the gas is commonly found on Earth escaping from magmatic vents. That could mean the same thing is happening on the Red Planet.
The release of this gas varies according to the Martian seasons, reaching maximum activity in the planet's northern hemisphere's winter then largely disappearing in the summer.
But scientists noticed spikes of hydrogen chloride in the northern hemisphere summer where it shouldn't have been – and during a period when it should have been quiet.
The gas release always seemed to occur during the same season and at the same place, above volcanic fissures around the Alba Mons volcano in early summer.
Mars is not dead, just dormant
Mars has the largest volcanoes in the Solar System, including the largest in the Solar System, Olympus Mons.
But it's not understood how active Mars's volcanoes really are.
Images captured by spacecraft orbiting the Red Planet show some volcanoes have been active within the last few million years.
Seismometers have also detected marsquakes, suggesting the planet could be volcanically active.
And yet no new lava flows or eruptions have ever been observed.
Finding Mars's volcanic smoking gun
First to be discovered was hydrogen chloride, localised in space just after the frosts of Martian winter.
Then the Trace Gas Orbiter found fresh, narrow fissures in the Alba Mons region. In some cases these were hundreds of metres long and accompanied by colour changes on the surface.
"The Trace Gas Orbiter was able to find the smoking gun. It was like looking for a needle in a haystack," says Daniel.
"It’s truly amazing that it spotted a handful of molecules from a perhaps intermittent source, whilst moving continuously along its orbit to monitor the whole Martian atmosphere."
The team suggest gases could be rising through the fissures once the freezing ice of winter begins to thaw during Martian summer.
And the change in colour around the fissures could be a result of deposits left behind by gases escaping from Mars’s interior.
"Looking at the spatial distribution of the seeping, it became instantly obvious to me that there was something volcanic behind it, but it had to be demonstrated," says Daniel.
"A huge part of the work consisted of examining all the possible chemical processes going on in the Martian atmosphere.
"We needed to be rigorous, critical and creative to explain the presence of hydrogen chloride. The data were complex, but also excellent brain food."
The team even think the seepage could be connected to a dormant magma chamber under the surface of Mars.
What it means for life on Mars
Scientists say magmatic gases like hydrogen chloride could have been more abundant on Mars in the past.
They could have contributed to ancient Mars's thicker atmosphere and warmer climate, when liquid water covered most of the surface of the planet.
If lava were rising through the planet's crust at that time, it could have led to warm, habitable spots on Mars.
"Looking for Martian life in the seeping fissures of the Alba Mons region would make a lot of sense," says Daniel.
"If hydrothermal systems are active, they could contain the ingredients and energy needed for microorganisms to develop and shield microorganisms from the hostile and changing environment above the surface."
