New studies indicate that the atmosphere of Mars, which significantly reduced around 3.5 billion years ago, might be trapped within the planet’s clay-rich crust. It is believed that water on Mars could have triggered reactions that extracted CO2 from the atmosphere and transformed it into methane within the clay minerals.
Mars wasn’t always the icy wasteland it appears to be now. There is growing evidence showing that water once flowed on its surface billions of years ago. If water was present, it implies that there was once a dense atmosphere to prevent this water from freezing. However, roughly 3.5 billion years ago, the water evaporated, and the once-abundant carbon dioxide in the atmosphere significantly decreased, leaving behind only a thin atmosphere that lingers today.
So, what happened to Mars’ atmosphere? This has been a longstanding mystery in the history of Mars, which spans 4.6 billion years.
Two geologists from MIT believe the answer might be found in the planet’s clay. In a study published in Science Advances, they suggest that a large portion of Mars’ lost atmosphere may be stored in its clay-covered crust.
The researchers argue that the presence of water on Mars could have allowed it to seep through specific rock types, initiating a gradual series of reactions that extracted carbon dioxide from the atmosphere, turning it into methane—a form of carbon that could be preserved within the clay for eons.
This process is similar to what’s observed in certain areas on Earth. The team utilized their understanding of rock-gas interactions on Earth to theorize how comparable processes could occur on Mars. Their findings indicate that the clay covering Mars could potentially trap up to 1.7 bar of carbon dioxide, which could represent about 80 percent of the planet’s original atmosphere.
The researchers speculate that this stored carbon on Mars could one day be extracted and converted into fuel for future missions between Earth and Mars.
“Our research on Earth implies that similar mechanisms likely worked on Mars, allowing significant amounts of atmospheric CO2 to have been transformed into methane and stored in clays,” says study co-author Oliver Jagoutz, a geology professor in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS). “This methane could still exist and might even provide energy for missions on Mars in the future.”
Leading the research is Joshua Murray, a recent graduate of EAPS.
In the folds
Jagoutz’s group at MIT aims to uncover the geological processes and interactions that shape the Earth’s lithosphere—the solid, outer layer encompassing the crust and upper mantle, where tectonic plates reside.
In 2023, he and Murray concentrated on a type of surface clay mineral known as smectite, recognized for its exceptional ability to trap carbon. Each grain of smectite contains numerous folds, providing a sanctuary for carbon to lie undisturbed for billions of years. They demonstrated that smectite on Earth likely resulted from tectonic processes, and once exposed, these clay minerals could absorb and store substantial amounts of carbon dioxide from the atmosphere, leading to global cooling over millions of years.
Shortly after sharing their findings, Jagoutz noticed a Mars surface map that indicated vast areas were covered with similar smectite clays. Could these clays have had a comparable carbon-trapping capacity on Mars, and if so, how much carbon could they store?
“We understand that this process occurs, and it’s well-known on Earth. These rocks and clays are also found on Mars,” Jagoutz notes. “So we aimed to connect the dots.”
“Every nook and cranny”
Unlike Earth, where smectite results from continental plate movements that bring deep rocks to the surface, Mars lacks tectonic activity. The team explored potential ways the clays might have formed on Mars, guided by existing knowledge about its history and makeup.
Remote sensing data of Mars hint that some parts of its crust may contain ultramafic igneous rocks, akin to those that generate smectites through weathering processes on Earth. Other geological patterns resemble terrestrial river systems, suggesting pathways where water might have flowed and interacted with surrounding rock.
Jagoutz and Murray pondered whether water might have interacted with Mars’ deep ultramafic rocks, resulting in the formation of the surface clays seen today. They created a straightforward model of rock chemistry based on how igneous rocks interact with their surroundings on Earth.
They applied this model to Mars, where it’s believed the crust largely consists of igneous rock rich in the mineral olivine. This model was used to foresee the transformations that olivine-rich rock might undergo if water existed on the surface for a billion years amidst a CO2-rich atmosphere.
“In that epoch of Mars’ past, we posit that CO2 was prevalent in every nook and cranny, with water percolating through the rocks saturated with CO2,” explains Murray.
Over approximately a billion years, as water passed through the crust, it would have slowly reacted with olivine—a mineral abundant in reduced iron. The oxygen molecules from the water would bond with iron, releasing hydrogen and forming oxidized iron, which gives Mars its distinctive red hue. This freed hydrogen would then unite with carbon dioxide in the water to create methane. Over time, olivine would gradually transform into another iron-rich rock type, known as serpentine, which continued to react with water, producing smectite.
“These smectite clays possess remarkable capacity for carbon storage,” remarks Murray. “Then we leveraged our knowledge of how these minerals store organic compounds in clays on Earth to estimate how much methane could potentially be stored within Martian clays if the surface features this much clay.”
He and Jagoutz determined that if Mars is enveloped by a layer of smectite measuring 1,100 meters in depth, this clay could enclose vast amounts of methane, analogous to most of the carbon dioxide believed to have been lost since the planet dried up.
“Our findings indicate that the projected global clay quantities on Mars could be sufficient to account for a significant portion of Mars’ initial CO2 being sequestered as organic compounds within the clay-rich crust,” Murray explains. “In some respects, Mars’ lost atmosphere may be right in front of us.”
This research was partly funded by the National Science Foundation.
