The case for life on Mars rests on two very different kinds of evidence. One looks back roughly four billion years, to massive mineral deposits in a southern basin that appear to have formed on the floor of a vanished sea. The other is happening now, or very recently: instruments aboard Europe’s ExoMars Trace Gas Orbiter have caught hydrogen chloride gas escaping from narrow fissures around Alba Mons, a signal researchers interpret as emissions from magma still lingering beneath the Martian surface. Both lines of evidence point to the same underlying ingredient—heat—and both frame Mars as a planet where the conditions associated with life’s emergence on Earth may have existed, and may still exist underground.

Mars’ Ancient Past: A Warm, Wet World with Seafloor Vents

In 2017, NASA’s Jet Propulsion Laboratory described an international report examining observations from the Mars Reconnaissance Orbiter of enormous deposits in the Eridania basin, a region of connected, quasi-circular basins in Mars’ southern hemisphere that may have originated as very ancient impacts. The study’s authors interpret the data as evidence that the deposits formed when heated water from a volcanically active part of the crust entered the bottom of a large sea, long ago.

What makes the find notable is its specificity. As JPL reported, sea-floor hydrothermal deposits add an important type of wet ancient environment to a list that already included rivers, lakes, deltas, seas, groundwater and hot springs. This is geological evidence—minerals laid down by warm, chemically reactive water at a seafloor—not a direct trace of life. But it identifies an area of Mars that may offer clues about how life originated on Earth, because it preserves the kind of environment where that origin is thought to have occurred.

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Modern Mars: Hints of Subsurface Volcanic Activity

The more recent evidence comes from a very different kind of observation. The Trace Gas Orbiter’s infrared spectrometers detected hydrogen chloride strongly localized in space, and in time—appearing just after winter frosts sublimate. A closer look at the Alba Mons region with the orbiter’s CaSSIS camera revealed fresh, narrow fissures, some hundreds of metres long, associated with color changes on the surface.

Scientists interpret the gas as emissions from hot magma below the regolith, and the research team suggests the seepage is connected to a dormant magma chamber—a kind of volcanic plumbing system under the Martian surface. The researchers suspect ice may block the fissures during much of the year, with thawing in early summer letting trapped volcanic gases escape. As Live Science reported, Alba Mons is the largest Martian volcano by surface area, and more research is still required to confirm the emissions. The detection is strong evidence for subsurface magmatic processes, not proof of active surface eruptions.

The biological logic of the finding is straightforward, though: if lava rising through the crust meets groundwater, warm, habitable niches could result. “Looking for martian life in the seeping fissures of the Alba Mons region would make a lot of sense,” the team argues.

The Engines of Martian Hydrothermal Systems: Magmatic and Radiogenic Heat

Not every hydrothermal system needs a volcano. Research published in Nature Communications by Lujendra Ojha and colleagues distinguishes two heat engines that could drive circulating, water-heating systems on Mars: magmatic heat from molten rock, and radiogenic heat from the slow decay of radioactive elements in the crust.

The difference matters for habitability. Magmatic systems depend on molten rock near the surface, which ties them to active volcanism. Radiogenic systems, by contrast, are fueled by uranium, thorium and potassium—elements with half-lives in the billions of years. Because of those long half-lives, the study’s authors write, radiogenic hydrothermal systems “can survive for >100 million years,” far outlasting magmatic or impact-driven ones. That longevity makes them prime targets for astrobiological exploration, and it means Mars’ potential for life is not limited to places where magma still moves.

The same study connects the two eras of this story: regions of Mars enriched in heat-producing elements during the Noachian period could have sustained hydrothermal circulation for a prolonged period—including, plausibly, the Eridania basin. The authors also note that radiogenic heat-driven hydrothermal systems may have been widespread on early Earth, when radioactive heat production would have been far higher than today.

Why Hydrothermal Systems are Cradles of Life

The reason scientists keep returning to vents, fissures and heated seafloors is that these environments bundle what prebiotic chemistry and microbial life require. As researcher Trokhimovskiy explained, rising magma can encounter, melt and heat underground water, “creating environments shielded from the harsh surface conditions,” and such active systems may provide the energy sources and favorable conditions needed to support microbial life.

The protection matters as much as the warmth. On Mars today, and probably on early Earth, the surface was hostile—thin or unstable atmosphere, radiation, cold. A submerged or buried hydrothermal system offers water, chemical energy, and a stable temperature refuge at once. In the past, magmatic gases like hydrogen chloride could even have contributed to a thicker atmosphere and warmer climate, allowing liquid water to cover much of the planet’s surface.

What researchers look for in such settings are biosignatures—preserved traces of organisms. One concrete example discussed in a 2024 study published in the Journal of Geophysical Research: Planets is stromatolites: rocks containing evidence of ancient layered mats of bacteria, visible to the naked eye, sometimes found on Earth in extreme environments such as geyser basins. On Mars, a returned sample could be examined for exactly such structures.

Comparative Analysis of Hydrothermal Environments

The table below brings the three environments into a single frame, so the parallels—and the gaps in what each line of evidence actually shows—can be read at a glance. It compares the geological record, the likely energy source, and the astrobiological significance of each setting.

Three hydrothermal environments relevant to the search for Martian life
Feature Ancient Mars (Eridania basin) Potential modern Mars (Alba Mons) Early Earth deep-sea vents
Environment type Ancient seafloor hydrothermal system Potential subsurface hydrothermal system (inferred) Radiogenic heat-driven systems thought widespread on early Earth
Location Eridania basin, southern Mars Rifts of Alba Mons, above a suggested dormant magma chamber Deep seafloors; specific settings not detailed in the evidence
Evidence Massive deposits interpreted as formed by volcanically heated water at a sea floor Localized hydrogen chloride gas and fresh fissures; not yet confirmed Life on Earth thought to have first emerged in hydrothermal systems
Heat source Volcanically active crust; radiogenic heat could sustain long-lived circulation Subsurface magma; retained internal heat Radiogenic decay, higher in the Hadean and Archean than today
Astrobiological significance May preserve clues about the origin of life; one of several known wet environments Warm, shielded niches where groundwater meets magma A leading candidate setting for where life arose

Read together, the rows show why the two Martian sites matter for different reasons: Eridania preserves a finished record of an Earth-like environment, while Alba Mons hints that the machinery of one may still be running.

Implications for the Search for Life on Mars

The synthesis supports a clear scientific posture: scientists should continue to prioritize the exploration of both ancient hydrothermal deposits and regions with evidence of recent subsurface magmatic activity on Mars. The ancient deposits offer searchable, preservable records of a warm, wet world; the gas-seeping fissures offer the possibility of environments that still exist today.

“Our findings suggest that Mars has retained enough internal heat to support volcanic activity until recently,” said Daniel Mège of the Space Research Centre of the Polish Academy of Sciences, a co-lead author of the Science Advances paper behind the detection, “and possibly still does.” Whether that retained heat—and the planet’s older hydrothermal record—ever translated into organisms remains unproven either way.

The measurable next steps are concrete: future missions detecting biosignatures in ancient deposits, or confirming active subsurface hydrothermal systems through direct sampling or further gas analysis, would settle whether Mars’ habitable environments crossed the same threshold Earth’s apparently did.

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