Mars, known as the Red Planet, has an intriguing past that diverges significantly from its current cold and desolate environment. Evidence suggests that billions of years ago, water once coursed across its surface, implying that it harbored a thicker atmosphere capable of preventing the water from freezing. However, around 3.5 billion years ago, this water evaporated, and the planet’s once dense atmosphere, rich in carbon dioxide, suffered drastic thinning, leaving behind only a faint atmosphere.
This evolution raises a critical question: What happened to Mars’ atmosphere? This enigma has puzzled scientists throughout Mars’ 4.6-billion-year history.
Two geologists from MIT may have found a piece of the puzzle in Martian clay. In a recent study published in Science Advances, they propose that a considerable part of Mars’ vanished atmosphere could be trapped within the planet’s clay-rich crust.
The researchers argue that as water existed on Mars, it could have seeped through certain rock formations, triggering a slow progression of reactions that drew carbon dioxide out of the atmosphere and converted it into methane — a stable form of carbon that could remain stored in the planet’s clay for millions of years.
This process mirrors those observed in various regions on Earth. The team leveraged their understanding of terrestrial rock-gas interactions to theorize how similar actions might have unfolded on Mars. They estimate that the vast expanse of clay covering Mars could potentially sequester up to 1.7 bar of carbon dioxide, which equates to roughly 80% of the planet’s original atmosphere.
The researchers also suggest that this trapped carbon could one day be utilized as fuel for future missions between Mars and Earth.
“Based on our findings from Earth, we show that comparable processes likely occurred on Mars, indicating that substantial amounts of atmospheric CO2 may have transformed into methane and been locked away in clays,” says Oliver Jagoutz, a geology professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “This methane could still exist and might even be harnessed as an energy source on Mars in the future.”
Leading the study is recent EAPS graduate Joshua Murray, PhD ’24.
Investigating Geologic Processes
Jagoutz’s team at MIT is dedicated to unraveling the geological processes that shape the evolution of Earth’s lithosphere, a term that describes the outer hard layer comprising the crust and upper mantle where tectonic plates exist.
In 2023, they focused on a specific clay mineral known as smectite, recognized for its remarkable capacity to trap carbon. Each smectite grain contains numerous folds, providing ample space for carbon to be securely stored for billions of years. They demonstrated that smectite on Earth likely originated from tectonic activity, which once exposed the clay minerals on the surface, allowing them to draw down and store substantial amounts of carbon dioxide from the atmosphere over millions of years, thereby cooling the Earth.
Shortly after presenting their results, Jagoutz looked at a map of Mars’ surface and discovered that much of it is covered with smectite clays. This raised a compelling question: Could these clays have similarly trapped carbon on Mars, and if so, how much?
“We understand this process occurs, and it is well-documented on Earth. Furthermore, we can find these rocks and clays on Mars,” Jagoutz remarks. “Therefore, we aimed to connect the dots.”
Understanding Mars’ Unique Geology
Unlike Earth, where smectite results from tectonic plate movements, Mars lacks such activity. Thus, the team sought to uncover how these clays formed on Mars by considering the planet’s history and geological composition.
Certain remote measurements suggest that parts of Mars’ crust may contain ultramafic igneous rocks, comparable to those that yield smectites through weathering on Earth. Additionally, some observations hint at geologic formations resembling rivers, indicating possible water flows interacting with the underlying rocks.
Jagoutz and Murray hypothesized whether water could have reacted with Mars’ deep ultramafic rocks, resulting in the formation of the prevalent clays. They devised a straightforward chemical model, applying their knowledge of how igneous rocks behave in Earth’s environment.
Using their model, they examined the conditions on Mars, where scientists believe the crust predominantly consists of olivine-rich igneous rock. They estimated how these rocks might have transformed over a billion years, assuming the presence of water and a thick carbon dioxide atmosphere.
“At that period in Mars’ history, we believe CO2 was ubiquitous, flowing through every crevice, and water interacting with these rocks was saturated with CO2 as well,” Murray explains.
Over approximately a billion years, the percolating water would slowly have reacted with olivine, a mineral abundant in a reduced form of iron. Oxygen from the water would bond with the iron, releasing hydrogen and creating the oxidized iron that gives Mars its characteristic red hue. The free hydrogen then combined with the dissolved carbon dioxide in the water, resulting in methane. As this reaction advanced, olivine progressively transformed into serpentine, which continued reacting with water to form smectite.
“These smectite clays possess immense capacity for carbon storage,” Murray states. “We drew upon existing knowledge of how these minerals are preserved in clays on Earth and extrapolated that knowledge. If the Martian surface harbors this much clay, how much methane could be stored there?”
Ultimately, Jagoutz and Murray found that if Mars is enveloped by a layer of smectite reaching 1,100 meters deep, the potential for methane storage could rival the majority of the carbon dioxide believed to have vanished since the planet dried up.
“We conclude that global estimates for clay volumes on Mars align with the idea that a substantial fraction of Mars’ original CO2 has been sequestered as organic compounds within the clay-rich crust,” Murray says. “In many respects, Mars’ missing atmosphere might be hiding in plain sight.”
“Understanding what happened to the CO2 from an early, denser atmosphere is a fundamental question in deciphering Mars’ climate history and potential habitability,” says Bruce Jakosky, a professor emeritus of geology at the University of Colorado and principal investigator for the Mars Atmosphere and Volatile Evolution (MAVEN) mission, which has been studying Mars’ upper atmosphere since 2014. While not involved in this specific research, Jakosky acknowledges its significance. “The findings by Murray and Jagoutz shed light on the chemical interactions of rocks with the atmosphere, a process that may have played a major role in removing CO2 from Mars’ early atmospheres.”
This research was partially supported by the National Science Foundation.
Photo credit & article inspired by: Massachusetts Institute of Technology
