Mars’ Atmosphere Might be Hiding in Plain Sight, New Research Suggests

New research suggests that Mars' missing atmosphere, long a mystery for planetary scientists, could be hiding within the planet's clay-rich surface. This surprising discovery sheds light on how carbon dioxide (CO2) from the early Martian atmosphere might have been chemically trapped in clays, primarily through interactions between water and certain types of rock, locking away significant portions of the planet's atmospheric gases.

The Atmospheric Puzzle of Early Mars

Billions of years ago, Mars was a vastly different world from the dry, cold planet we see today. Evidence gathered from Martian rovers and satellite observations suggests that Mars had flowing rivers, lakes, and perhaps even oceans. For liquid water to exist on the surface, Mars would have needed a thick atmosphere to trap heat, keeping temperatures above freezing. Most scientists agree that early Mars had an atmosphere dominated by carbon dioxide, which acted as a greenhouse gas, insulating the planet and making it potentially habitable.

However, about 3.5 billion years ago, Mars underwent a drastic transformation. The atmosphere thinned, temperatures dropped, and the planet lost its surface water. For decades, researchers believed that this atmospheric loss was primarily due to solar winds stripping away Mars' protective envelope of gas after the planet lost its magnetic field. While this process explains part of the atmosphere's disappearance, recent research highlights that it may not be the whole story. According to Joshua Murray, the lead author of the new study, “Current rates of loss to space can explain less than 1 percent of the early atmosphere when extrapolated back into the past.” This prompted researchers to look for other mechanisms that could explain where Mars' thick atmosphere had gone.

How Clay Minerals May Hold the Key

The new study, led by researchers from the Massachusetts Institute of Technology (MIT) and published in Science Advances, proposes a novel explanation: Mars' missing atmosphere may not have been lost to space but rather absorbed by its own surface, particularly through chemical reactions involving clay minerals. On Earth, a similar process occurs when CO2 from the atmosphere is trapped in smectites, a type of clay known for its carbon-storing properties. Smectites are created when ultramafic rocks, which are rich in olivine, react with water.

The study suggests that a comparable process may have occurred on ancient Mars. As water trickled through Mars' igneous rocks, the resulting chemical reactions converted atmospheric carbon dioxide into methane, which was then stored in the clay. This methane could remain trapped in the Martian crust for billions of years. According to Oliver Jagoutz, a co-author of the study, “Based on our findings on Earth, we show that similar processes likely operated on Mars and that copious amounts of atmospheric carbon dioxide could have transformed to methane and been sequestered in clays.”

These clays could have locked away significant portions of Mars' carbon, leading to the depletion of its atmosphere over time. The team used a geological model based on Earth's processes to estimate how much CO2 could have been stored in Mars' clays. Their findings indicate that the Martian surface could hold as much as 1.7 bar of CO2—which is approximately 80% of the planet's initial atmosphere. In essence, Mars' ancient atmosphere might still be there, just trapped beneath the surface.

The Role of Smectites and Methane in Atmospheric Loss

One of the central components of the study is the role of smectites, which are found in abundance on the Martian surface. Smectites are layered minerals with an exceptional capacity to store gases like CO2, locking them away for billions of years. While on Earth, tectonic activity constantly recycles carbon stored in clays, Mars does not have active tectonic plates. This lack of tectonic recycling on Mars means that once carbon is trapped in smectites, it could remain there indefinitely.

Using satellite data and rover observations, scientists have found extensive clay deposits across Mars. According to Murray, “There is plenty of evidence for a thick clay layer on the Martian surface. Almost 80 percent of satellite spectra detect these high-surface-area clay minerals on the Martian surface. Clay has been detected in craters as deep as 17 kilometers [10.5 miles].” The presence of such extensive clay deposits suggests that Mars' surface has been absorbing CO2 for billions of years, providing a possible answer to the long-standing question of where Mars' atmosphere went.

The process of trapping CO2 in smectites begins with the reaction between water and olivine. This reaction produces serpentine, which slowly transforms into smectites. As serpentine and smectites form, they trap methane—created when hydrogen freed during the reaction bonds with CO2. This methane remains locked within the clay-rich crust, preventing it from escaping back into the atmosphere.

Implications for Future Mars Exploration

The idea that Mars' atmosphere is not lost but hidden beneath its surface opens new possibilities for both planetary science and future Mars exploration. If methane and CO2 are still trapped in the planet’s clays, these gases could potentially be extracted and used as a resource. Methane, in particular, could serve as a fuel for future human missions to Mars, providing a critical resource for long-duration exploration of the Red Planet.

This discovery also helps scientists better understand Mars' climate history. By studying the interactions between water, rocks, and atmospheric gases, researchers can piece together how Mars evolved from a warm, wet world into the cold desert we see today. Murray explains, “If the Martian surface has this much clay in it, how much methane can you store in those clays?” Answering this question could reveal more about the planet's early atmospheric composition and how it changed over time.

The new findings also challenge previous assumptions about how planets lose their atmospheres and may have implications for understanding other rocky planets. The research suggests that the geological processes trapping atmospheric gases in surface minerals could be more common than previously thought. This insight could apply not just to Mars but to other planets or moons with ancient atmospheres, expanding our knowledge of planetary evolution.

Could Mars' Atmosphere be Restored?

While the notion of tapping into Mars' methane-rich clays is an exciting prospect for future exploration, the researchers caution that much more work is needed to confirm the extent of CO2 and methane sequestered within the planet’s surface. Even if these gases can be accessed, releasing them back into the atmosphere would be a complex task, requiring advanced technologies that are still years away from development. However, if successful, it could potentially lead to the terraforming of Mars, making the planet more hospitable for future human missions.

In conclusion, the discovery that Mars' atmosphere may be hidden within its clay-rich crust represents a significant breakthrough in planetary science. The research offers a compelling new explanation for how Mars lost its atmosphere and opens exciting possibilities for using these trapped gases in future exploration. With further study, scientists hope to unlock more secrets about the Red Planet's ancient climate and its potential for supporting human life in the future.