The search for life beyond Earth is one of humanity’s oldest and most exciting goals. For years, scientists have pointed their telescopes and sent their robotic explorers toward Mars, our closest planetary neighbor, hoping to find a sign that we are not alone. Mars today is a cold, dry, dusty place, but we know it once had liquid water, which is essential for life as we know it. One of the biggest clues, and the source of the most intense scientific debate, is the detection of a simple gas in the Martian atmosphere: methane ($\text{CH}_{4}$).
Methane is a molecule made of one carbon atom and four hydrogen atoms. On Earth, the vast majority—over 90%—of the methane in our atmosphere comes from living things, such as microbes called methanogens, or from human activities like farming and industry. Because life produces so much of it on our planet, finding even tiny amounts of methane on Mars immediately captured the world’s attention. If it’s there, it must be produced by something, and that something could be life, either living right now or active in the very recent past. The alternative is that some geological process is at work, but the way this gas appears and disappears on Mars is strange and doesn’t fit easily with simple rock chemistry.
This small, invisible gas has become a massive question mark hanging over the Red Planet. Its presence suggests that Mars is not a dead world, but one that is still active in some way—biologically or geologically. The mystery is less about whether the methane exists, and more about what is creating it, and why the different missions sent to Mars don’t always agree on how much of it is there. So, what exactly is it about this elusive Martian gas that makes it the center of the debate about life?
What Makes Methane an Important “Biosignature” for Life on Mars?
A biosignature is any substance, object, or pattern whose presence or abundance requires a biological origin. Methane fits this description perfectly because of how frequently it is produced by life on Earth. Microbes, which are tiny organisms, are constantly releasing methane as a waste product when they digest nutrients. These organisms are incredibly robust and have been found thriving in extreme environments on Earth, such as deep underground or in very hot or cold places. Scientists believe that if life exists on Mars, it would likely be found deep below the surface, protected from the planet’s harsh radiation and cold temperatures.
Since Mars has very little geological activity—it doesn’t have active volcanoes like Earth to pump out gases—any methane that is detected in the atmosphere is expected to break down quickly. Solar radiation, specifically ultraviolet light, destroys methane molecules in a process called photolysis, giving the gas a lifetime of only a few centuries (around 300-600 years) in the Martian air. This is a very short time in the history of a planet. If scientists keep finding methane today, it means that something is actively putting it into the atmosphere right now to replenish the supply. It cannot be gas left over from when Mars formed billions of years ago. Therefore, the detection of methane is proof of an active process, and one of the most exciting possibilities for that active process is life.
How Did Scientists First Discover Methane on the Red Planet?
The search for methane on Mars has a long and complicated history, dating back to early claims that were later retracted. The first reliable detections of methane came from Earth-based telescopes in 2004, and these were later confirmed by the European Space Agency’s (ESA) Mars Express orbiter. These initial measurements were a major breakthrough, reporting a global average of a few parts per billion (ppb) of methane in the atmosphere, and even suggesting that there were plumes or patches of higher concentration. The amount of methane was tiny—far less than on Earth—but its presence was significant.
Following these initial findings, NASA sent the Curiosity rover to the surface of Mars in 2012, landing in Gale Crater. Curiosity carries a very sensitive instrument called the Tunable Laser Spectrometer (TLS), which is part of the larger Sample Analysis at Mars (SAM) chemistry lab. The TLS is designed to “sniff” the atmosphere and look for the unique chemical fingerprint of methane. Curiosity’s in-situ (on-site) measurements confirmed that methane is definitely present and, critically, showed that the amount of the gas changes both with the seasons and through random, sudden “spikes.” This variability only deepened the mystery, suggesting a localized source that turns on and off.
Can Geological Processes Create Methane Without Any Life?
Yes, they absolutely can, and this is the main alternative explanation that scientists are exploring. On Earth, there are geological ways to create methane, and the same processes might be at work deep beneath the Martian surface. The most common non-biological process that could create methane on Mars is called serpentinization. This happens when water reacts with certain iron-rich minerals, such as olivine and pyroxene, which are known to be abundant on Mars.
In simple terms, when water seeps down and interacts with these specific rocks under the right amount of heat and pressure, a chemical reaction occurs. This reaction produces a mineral called serpentine, along with hydrogen gas ($\text{H}_{2}$). The hydrogen gas can then react with carbon dioxide ($\text{CO}_{2}$), which is the main component of the Martian atmosphere, to create methane. This process is most likely to happen deep underground where it is warm enough for liquid water to exist, even if it’s too cold for it on the surface. Another possibility is that the methane is ancient gas trapped in “ice cages” called clathrates, which are structures of frozen water that can store gas molecules. If these clathrates are warmed up—perhaps due to seasonal changes or geological events—they could release a sudden puff of trapped methane into the air.
Why Do Curiosity’s and TGO’s Methane Readings Disagree So Much?
The most confusing part of the Mars methane mystery is the disagreement between the measurements taken on the surface and those taken from orbit. NASA’s Curiosity rover, on the surface of Gale Crater, consistently detects a low level of methane that rises and falls with the seasons, and it sometimes sees sudden, high “spikes” of the gas. Meanwhile, the European Space Agency’s ExoMars Trace Gas Orbiter (TGO), which arrived at Mars in 2016 and has a much more sensitive instrument, has reported very little to no methane in the Martian atmosphere, setting a very low global upper limit.
This is a huge puzzle. If methane is being released, as Curiosity detects, TGO should be able to see it, especially since it is so sensitive. The discrepancy has led to intense debate. One idea is that the methane detected by Curiosity is being destroyed or removed from the atmosphere much faster than current science models predict. If there’s an unknown, quick-acting “methane sink” that removes the gas just above the surface, then the low levels observed by TGO from higher up would make sense. Another possibility, which scientists are still investigating, is that the methane source is extremely localized—perhaps coming from a small fault line very close to the Curiosity rover—and is quickly dispersed or destroyed before it can reach the higher altitudes where TGO is looking. Some scientists have even explored the chance that the gas detected by Curiosity might, in part, be contamination from the rover itself, though its design was carefully made to avoid this.
How Does the Seasonal Change in Methane Offer Clues?
The fact that the background level of methane detected by Curiosity rises and falls predictably with the seasons provides one of the strongest clues about its source. Curiosity found that the methane concentration is typically highest during the Martian summer and lowest during the winter. This seasonal change is far greater than what would be expected from simple changes in atmospheric pressure.
This strong correlation with the seasons suggests a process that is somehow temperature-dependent. For a biological source, warmer temperatures could allow buried microbes to become more active and produce more methane. For a geological source, the warmer summer months might cause the shallow subsurface ice or soil to warm up just enough to release trapped gas. Imagine a soda bottle: shaking it up and warming it slightly makes the gas escape faster when you open the lid. On Mars, the methane might be trapped in soil or ice just below the surface and the subtle warming of the seasons is the process that “opens the lid” to let the gas leak out. The seasonal pattern indicates an ongoing, repeatable mechanism, whether it is life or a non-biological chemical process.
What Are Scientists Doing in 2025 to Finally Solve the Mystery?
The mystery of Mars methane is a top priority for space missions today, and scientists are using every tool they have to try and solve it. In 2025, the focus is less on finding the methane and more on determining its origin. Scientists are working on a few key areas to move the debate forward.
First, they are using more advanced computer models to better understand how methane moves through the thin Martian atmosphere. These simulations can help them pinpoint where a gas source would need to be located to produce the specific patterns seen by Curiosity, while also remaining consistent with TGO’s non-detections. Second, new instruments are being developed or proposed that can do something critical that current missions cannot: measure the isotopic signature of the methane. Isotopes are atoms of the same element (like carbon) that have a different mass. Methane produced by living organisms (biotic) often has a slightly different ratio of carbon isotopes than methane produced by geological processes (abiotic). Finding this isotopic “fingerprint” would be the closest thing to a definitive answer about whether life is involved. The search is becoming less about ‘is it there?’ and more about ‘where did it come they come from, and what is the carbon made of?’
The presence of methane on Mars has profoundly changed our view of the planet. It proves that Mars is not an inert, completely dead world, but one with dynamic and active processes that we do not fully understand. Whether the methane is a product of tiny, resilient microbes living deep underground or the result of a strange chemical reaction between rock and water, its existence forces us to confront the possibility of an active Martian world. The sporadic appearances and disappearances of this gas, combined with the conflicting measurements from rovers and orbiters, makes the Red Planet’s atmosphere the ultimate scientific enigma. Ultimately, solving this mystery is the key to knowing the planet’s history and whether life ever did—or still does—call Mars home.
What do you think is a more likely answer to the methane mystery: geology or biology?
FAQs – People Also Ask
What is the chemical composition of methane?
Methane is a very simple organic molecule with the chemical formula $\text{CH}_{4}$. It is made up of a single carbon atom that is bonded to four hydrogen atoms. It is the main component of natural gas and is a colorless, odorless gas that acts as a potent greenhouse gas both on Earth and in any planet’s atmosphere.
What is the “methane sink” on Mars?
The term “methane sink” refers to a process that removes methane from the atmosphere. On Mars, the main known sink is the sun’s ultraviolet radiation, which breaks down the methane molecule. However, since the observed methane disappears much faster than this process alone can account for, scientists believe there must be a faster, unknown sink, such as a chemical reaction with Martian dust or surface minerals, that is quickly destroying the gas near the surface.
How much methane is in the Martian atmosphere compared to Earth?
The amount of methane detected on Mars is extremely small, typically measured in parts per billion by volume (ppbv). Curiosity’s background measurements are usually less than one ppbv. In comparison, the Earth’s atmosphere has over 1800 ppbv of methane, which is thousands of times more concentrated. This difference means the Martian methane is a trace gas, making its detection and study very difficult.
Is the methane found on Mars proof of current life?
No, the methane found on Mars is not definitive proof of current life. While life is a strong candidate, the gas could also be produced by geological processes, such as the reaction between water and rock, which does not require any living organisms. To prove life is the source, scientists would need to find a biological “fingerprint,” like a specific isotopic ratio, or find the microbes themselves.
What is serpentinization and why is it important for Mars methane?
Serpentinization is a geological process where water reacts with iron-rich minerals like olivine under heat and pressure, forming serpentine minerals. This reaction releases hydrogen gas, which can then combine with carbon to form methane. It is important because it is a plausible, non-biological way to create a continuous supply of methane on Mars, even without active volcanoes or a strong internal heat source.
What is the difference between a high “spike” and the “background” methane level?
The background level of methane is the very low, persistent concentration of the gas that is constantly present in the atmosphere of Gale Crater, which Curiosity measures to vary predictably with the seasons. A spike is a sudden, high increase in methane concentration—sometimes ten times higher than the background—that appears randomly and lasts for only a short period. The background suggests a steady, seasonal mechanism, while the spikes suggest a sudden, localized release event.
What is the role of the ExoMars Trace Gas Orbiter (TGO) in the debate?
The TGO’s role is to act as a highly sensitive global watchdog for trace gases, including methane, from orbit. Its non-detection of a global methane background means that if the gas exists, it must be concentrated very close to the surface, released in very short bursts, or destroyed much faster than models predict. Its data places a strict upper limit on the total amount of methane in the atmosphere, challenging the interpretation of Curiosity’s measurements.
Could the detected methane be contamination from the Curiosity rover?
Scientists have taken great care to investigate the possibility of contamination. While there is a very small amount of terrestrial methane that may have been sealed into the instruments before launch, sophisticated tests have largely ruled out the rover as the main source of the large, seasonal and spike variations. The fact that the methane concentration changes so dramatically and predictably suggests it is a product of the Martian environment, not the rover itself.
What is an isotopic signature and how can it help solve the methane mystery?
An isotopic signature involves measuring the ratio of different versions of the same atom, called isotopes, within a molecule like methane. For example, carbon-12 and carbon-13 are two isotopes of carbon. Living things prefer to use lighter isotopes (like carbon-12) to produce methane, while geological processes produce a different ratio. Scientists hope that measuring this ratio in the Martian methane will act as a “fingerprint” to definitively distinguish between a biological or non-biological source.
Why is it so difficult to reconcile the different methane measurements on Mars?
It is difficult to reconcile the measurements because they seem to contradict basic atmospheric physics. Methane should mix easily and quickly across the atmosphere, meaning both the ground-based rover and the orbiting satellite should see a similar background level. The fact that the rover sees a background and spikes, while the orbiter sees almost nothing, implies either a huge measurement error, an unknown, extremely fast methane destruction mechanism, or a source that is only releasing gas in a highly localized and transient way.