Mars' hidden secret: Atmosphere trapped within ancient crust

Geologists from the Massachusetts Institute of Technology (MIT) argue that a significant portion of Mars's atmosphere may be hidden in its crust. They are referring to carbon dioxide that has been transformed into methane and trapped in clay layers.

As the scientists from MIT remind us, Mars wasn't always the desert planet we know today. According to collected information, extensive water reservoirs existed on the Red Planet billions of years ago. However, about 3.5 billion years ago, the water vanished, and the thick atmosphere rich in carbon dioxide thinned significantly. Planetologists have been pondering what exactly happened to the Martian atmosphere for years.

According to MIT experts, most of Mars's atmosphere may be hidden in rocks, specifically in the clay present in the planet's crust.

"Based on our findings on Earth, we show that similar processes likely operated on Mars and that copious amounts of atmospheric CO2 could have transformed to methane and been sequestered in clays," says Professor Oliver Jagoutz, author of the publication that appeared in the journal "Science Advances."

Scientists explain that when water was present on Mars, chemical reactions could have occurred due to its interaction with iron. The result of these reactions was the transformation of carbon dioxide into methane. The clay then absorbed this methane. According to Jagoutz, methane could still be there, which means there is a chance of using it as an energy source in the future.

Experts estimate that up to 80 per cent of Mars's former atmosphere could be hidden in the clay. In their theory, the researchers based their findings on similar chemical reactions observed on Earth.

Last year brought additional research on the mineral called smectite. Its characteristic is that it strongly absorbs carbon. On Earth, smectite was likely the product of tectonic activity. Once on the Earth's surface, such minerals stored significant amounts of carbon dioxide, which could have contributed to the planet's cooling over millions of years.

After examining maps of Mars, scientists noticed that a large part of the planet's surface is covered with clay containing smectite. This layer reaches a depth of more than 1 kilometre. However, Mars lacks the tectonic activity that would create this mineral. Therefore, scientists developed a model to explain how smectite could have been produced in the Martian crust.

"We find that estimates of global clay volumes on Mars are consistent with a significant fraction of Mars’ initial CO2 being sequestered as organic compounds within the clay-rich crust," says Professor Murray.

"In some ways, Mars’ missing atmosphere could be hiding in plain sight," he adds.