Mars Has a Gas Problem. Scientists Can’t Agree on Whether It’s Even Real.

The 20-Year Methane Debate That Could Answer the Biggest Question in Space Exploration and Why the Evidence Keeps Contradicting Itself

Photo by Planet Volumes on Unsplash

Sixty years of robotic exploration have produced a picture of Mars that is difficult to romanticize. Cold, thin-aired, bathed in radiation, desiccated to a degree that makes the Atacama look hospitable. Every rover we have sent has confirmed the same portrait: a surface where liquid water cannot persist, where organic molecules survive poorly, if at all, and where anything resembling life as we understand it would struggle to exist for long.

And yet, for over twenty years, a simple gas has kept a heated scientific debate alive. Methane is a molecule so basic it has four atoms. Its possible presence on Mars has never been confirmed to everyone’s satisfaction, and never convincingly ruled out either.

This difference is significant because, on Earth, methane is primarily produced by living organisms or geological processes associated with environments suitable for life.

The Environment That Makes This Question So Difficult

The picture Mars presents is one of compounding hostility: while the average surface temperature runs around -63°C, with swings that push the poles below -120°C, the equator briefly touches 20°C on a summer afternoon before plunging back to glacial cold. The atmosphere is composed of roughly 95% carbon dioxide, with traces of nitrogen and argon, at a pressure of approximately 6 millibars — less than one percent of Earth’s. At that pressure, liquid water cannot persist at the surface.

It either freezes or converts directly to vapor, bypassing the liquid state. The total water vapor in Mars’s atmosphere, if condensed, would form a film just tens of micrometers thick spread across the entire planet.

There is also no global magnetic field to deflect cosmic rays, and an atmosphere too thin to absorb ultraviolet radiation effectively. For any organism exposed at the surface, the environment combines extreme cold, near-vacuum pressure, and a continuous bombardment of radiation.

This is the context in which the methane question sits. Mars appears lifeless. The physics says it probably is. But a gas that should not be there, detected intermittently by instruments with conflicting results over two decades, keeps refusing to disappear from the scientific conversation entirely.

Twenty Years of Detections That Are Impossible to Confirm

The story begins in the early 2000s. Data from the European Space Agency’s Mars Express orbiter and ground-based telescope observations have hinted at the potential presence of small amounts of methane, in the order of a few tens of parts per billion, within the Martian atmosphere. Shortly after, reanalysis of data from Mars Global Surveyor was also interpreted as consistent with the presence of the gas in certain regions. Both sets of results came with important caveats: they were at the limit of the instruments’ sensitivity, and the quantities involved were small enough that instrumental artifacts or interpretation errors could not be ruled out.

The more significant development came in 2012, when NASA’s Curiosity rover arrived at Gale Crater and began taking atmospheric measurements. After months of initially negative results, the rover started detecting methane at low concentrations — not consistently, but intermittently, with occasional spikes considerably above the baseline. Over time, the data suggested a seasonal pattern: concentrations appear to rise during the Martian summer and fall as temperatures drop.

If this variation is real, it implies something active. A seasonal cycle of methane concentration does not arise from a static ancient reservoir; it requires a source that responds to changing conditions on the planet. That observation alone elevated the debate from an instrumental curiosity to a question about whether Mars is currently, right now in 2026, producing methane through some ongoing process.

The complicating factor is that all of Curiosity’s methane detections have hovered near the instrument’s detection threshold. The amounts are small enough that separating genuine atmospheric methane from measurement noise requires careful analysis, and different teams analyzing the same data have reached different conclusions. Over two decades in, the basic question of whether Mars actually produces methane remains genuinely unresolved.

The Spacecraft That Made It Worse

In 2016, the European Space Agency launched the ExoMars Trace Gas Orbiter (TGO) specifically to address this debate. TGO’s spectrometers are far more sensitive than any instrument previously deployed at Mars. Its mission was to confirm the methane detections, map their sources, and determine once and for all whether the gas is real and where it comes from.

It found nothing.

Since beginning its science mission in 2018, and across eight years of observations as of mid-2026, TGO has not detected any methane in the Martian atmosphere. The upper limit set by TGO is 0.05 parts per billion by volume, which is 10 to 100 times lower than the concentrations Curiosity had previously reported. Even flying directly over Gale Crater — Curiosity’s home — the orbiter found nothing, despite the rover having reported methane at that same location.

As one TGO researcher summarized: “We have a thousand times better sensitivity than the instruments on Curiosity, but we do not see any sign of methane absorption in the Martian atmosphere.”

The Nature paper reporting TGO’s initial non-detection described the contradiction plainly: to reconcile the surface detections with the orbital non-detections, methane would have to be destroyed in the lower atmosphere approximately a thousand times faster than current atmospheric chemistry models predict. A mechanism capable of doing that has not been confirmed.

This is the state of the science today. The rover on the surface is reporting intermittent methane. An orbiter equipped with far superior instruments, viewing the same atmosphere from above, reports no such thing. Both instruments are functioning correctly. The data are not reconcilable with what we know about how atmospheres mix.

Why This Gas Matters So Much

If methane were ordinary, we wouldn’t care. What makes this debate consequential is what methane can tell us about a planet’s activity — and what it cannot.

On Earth, approximately 35% of atmospheric methane is produced by living organisms. Methanogenic archaea are single-celled microorganisms that thrive in oxygen-deprived environments: wetland sediments, deep subsurface rock, and the digestive systems of livestock. They extract energy from chemical reactions involving hydrogen and carbon dioxide, releasing methane as a byproduct. They are among the oldest known forms of life, capable of surviving in environments that would be lethal to most other organisms.

If comparable microorganisms existed today on Mars, buried several meters or kilometers beneath the surface, they too could produce methane that would slowly migrate upward and eventually escape into the atmosphere. The seasonal variation Curiosity observed is consistent, at least qualitatively, with what you would expect if the rate of methane release from the subsurface varied with surface temperature.

The other reason methane matters is its instability. Under the ultraviolet radiation of the Martian sun and the photochemical reactions it drives, methane has a predicted atmospheric lifetime of a few hundred years. On geological timescales, that is essentially instantaneous. If methane is detectable in the Martian atmosphere today, it means a source must have replenished it recently, perhaps continuously. Geological events might release ancient methane that has been preserved in the Earth’s crust for eons, yet the seasonal fluctuations detected by Curiosity don’t readily align with a straightforward leakage hypothesis.

Methane is not proof of life. But it is a potential biosignature — a signal that cannot exist in Mars’s current atmospheric chemistry without some ongoing active process producing it. And identifying what that process is lies at the heart of whether Mars is currently habitable.

The Geological Alternative

The most serious non-biological explanation is a process called serpentinization. When certain iron-and magnesium-rich rocks react with liquid water under conditions of elevated temperature and pressure, they produce hydrogen. That hydrogen can subsequently react with carbon dioxide — abundantly available in Mars’s atmosphere — to generate methane through a purely abiotic process. Serpentinization is well-documented on Earth, occurring at mid-ocean ridges and in certain rock formations. It requires no biology. It requires only the right minerals, heat, and water.

Crucially, serpentinization requires liquid water somewhere in the system. Should this be happening underground on Mars, the water available would be scarce. It might exist as thin films sustained by geological heat, rather than in larger liquid bodies. But that itself is an interesting observation: a subsurface environment containing liquid water under elevated pressure, with chemical energy from rock-water interactions, is exactly the environment where methanogenic archaea thrive on Earth. The geological and biological scenarios are not as cleanly separable as they might initially appear; they implicate similar subsurface conditions.

An alternative theory suggests that methane, trapped in ice-like clathrates underground for eons, is gradually being released as the planet’s core heats. Another possibility is that methane is generated through thermolytic reactions fueled by lingering geological warmth deep within the Earth’s crust. Scientists also propose that methane might be released from clathrates, which are ice-like structures in the subsurface where methane has been frozen for billions of years, as the planet’s interior warms. This process could be complemented by the production of methane through thermolytic reactions, powered by residual geological heat in the deep crust.

These scenarios do not require liquid water or ongoing geological activity at the scale serpentinization implies. Their weakness is that they predict a steadier, more gradual release rather than the seasonal variation Curiosity observed, which is harder to explain without invoking a temperature-sensitive mechanism.

At present, no available data allows scientists to determine which of these scenarios is operating, or whether multiple mechanisms contribute simultaneously.

The Dust Devil Hypothesis

One of the most promising current attempts to reconcile TGO’s non-detection with Curiosity’s measurements involves the near-surface chemistry of Mars itself. Research into Martian atmospheric dynamics has proposed that the tiny electrical discharges produced by dust devils and Martian dust storms — swirling vortices that traverse the planet’s surface continuously — may generate highly reactive chemical species in the lowest layer of the atmosphere. These reactive species could destroy methane far more rapidly than models based on standard photochemistry predict, potentially breaking down the gas within a region so close to the surface that TGO’s orbital measurements, which access altitudes above a few kilometers, would never see it.

This hypothesis would allow both instruments to be correct simultaneously.

Curiosity measures methane within meters of the surface, where it exists transiently before being destroyed by electrochemical reactions driven by charged dust particles. TGO measures several kilometers above, where the gas has already been eliminated. The local chemistry of Martian dust activity, rather than any error in either instrument, would explain why two highly capable detectors produce incompatible results from the same planetary atmosphere.

This remains an active area of research, not a settled explanation. Confirming it would require direct measurement of the reactive species involved at the surface, which no current Mars instrument can do.

What Comes Next?

The investigation moves forward on two parallel tracks.

The first is the Rosalind Franklin rover, ESA’s next Mars surface mission. Unlike every rover that preceded it, Rosalind Franklin will be capable of drilling to two meters below the surface — well past the uppermost layer continuously sterilized by radiation. If organic molecules or biosignatures are present on Mars, they are most likely to be preserved at depth. Even if the rover cannot detect active life, it can characterize the chemical environment at subsurface levels and assess whether the conditions are compatible with biological activity. The sample obtained from a two-meter borehole on Mars will be a unique discovery, never studied before.

The second track involves the continued refinement of atmospheric models. The disagreement between Curiosity and TGO highlights a gap in our understanding of Mars’s lower atmosphere, potentially due to unrevealed chemistry or ambiguity in methane sources. Every mission adds constraints. Every non-detection tells you something about where the gas is not and at what concentrations it cannot exist.

The deeper truth here is that the methane debate illustrates how science actually works at its frontier. An unexpected measurement generates a hypothesis. New missions designed to test that hypothesis sometimes confirm it and sometimes produce incompatible results. The scientists then have to generate new models capable of accounting for all the contradictory data simultaneously, which requires new experiments, which generate new results, some of which contradict each other.

The ongoing investigation into Martian methane, whether it ultimately leads to confirmation, refutation, or an explanation tied to near-surface chemistry that leaves the question of subsurface biology open, is steadily yielding a richer understanding of a world that is far more intriguing than its barren photographs convey. A few molecules of a simple gas, possibly present, possibly not, possibly biological, possibly geological, have driven two decades of scientific effort and are about to drive a drill into Mars’s subsurface looking for an answer.

That is not a small question hiding behind a small gas. That is the biggest question in planetary science, expressed in parts per billion.

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Sources:
Nature, ESA — ExoMars Trace Gas Orbiter, ESA — First results from TGO, ESA — Mars orbiters did not see Curiosity methane burst.