Mars was not always the cold, desolate desert we see today. There is more and more evidence that water once flowed across the surface of the red planet, which requires the existence of a thick atmosphere, but suddenly the atmosphere thinned out and Mars became dry
Mars was not always the cold, barren desert we see today. There is increasing evidence that water once flowed across the surface of the Red Planet, billions of years ago. And if there was water, there must also have been a thick atmosphere that prevented the water from freezing. But at some time about 3.5 billion years ago, the water dried up and the air, once rich in carbon dioxide, became thin, leaving only a trace of the atmosphere that clings to Mars today.
Where exactly did the atmosphere of Mars go? That question is a central mystery for scientists studying the 4.6 billion years of Mars' history.
Two geologists from MIT suggest in a paper in Science Advances that much of Mars' missing atmosphere may be locked up in its clay-covered crust.
They argue that when there was water on Mars, the liquid may have seeped through certain types of rock and started slow chain reactions that gradually pulled carbon dioxide from the atmosphere and turned it into methane—a form of carbon that can be preserved for eons in the clayey face of Mars.
Similar processes occur in certain regions of the Earth. The researchers used their knowledge of interactions between rocks and gases on Earth and deduced from it how similar processes could have occurred on Mars. They found, given the amount of clay estimated to cover the surface of Mars, that the clay could contain up to 1.7 bar of CO2, equivalent to about 80% of the early, starting atmosphere of the star.
It may one day be possible to recover this hidden reddish carbon and convert it into fuel to be used for future missions between Mars and Earth, the researchers suggest.
"Based on our findings on Earth, we show that similar processes were likely at work on Mars, and these abundant amounts of CO2 Atmospherics turned into methane and buried in the clay," said Oliver Yagotz, one of the authors of the study. "It is possible that this methane is still on Mars and could be used there as a source of energy in the future."
Yigotz's group at MIT seeks to identify the geological processes and interactions that drive the development of the Earth's lithosphere - the hard, brittle outer layer that includes the crust and upper mantle, where the tectonic plates lie.
In 2023, he and Joshua Murray, the paper's lead author, focused on a type of clay mineral called smectite that is found on Earth's surface and is known to be a very effective trap for carbon. One grain of smectite has many folds, within which carbon can be undisturbed for billions of years. They showed that the smectite on Earth is likely the product of tectonic activity, and once exposed on Earth's surface, the clay minerals acted to attract and sequester CO2 in an amount that was enough to cool the land for millions of years.
Shortly after the team reported their results, Yegotz happened to look at a map of the surface of Mars and realized that much of the Martian surface is covered with the same smectite clay. Did the clay have a similar carbon-trapping effect on Mars, and if so, how much carbon could the clay store?
"We know that this process happens, and it is very well documented on Earth. And these rocks and clay exist on Mars," says Yagotz. "So we wanted to tie things together."
Unlike on Earth, where smectite is the result of the displacement and uplift of continental plates that bring rocks from the mantle to the surface, on Mars there is no such tectonic activity. The team looked for ways in which the clay could have formed on Mars, based on scientific knowledge of its history and composition.
For example, there are remote measurements of the surface of Mars that show that at least part of its crust contains ultramafic basic rocks (rich in iron and magnesium oxides), similar to the rocks that produce smectite through weathering in Israel. Other observations reveal geological patterns similar to terrestrial rivers and tributaries, where water could flow and react with the bedrock.
Yegotz and Marie wondered whether water might have reacted with the deep ultramafic rocks of Mars in a way that created the clay that covers the surface of Mars today. They developed a simple model of rock chemistry, based on what is known about how basic rocks interact with their environment on Earth.
They applied this model to Mars, whose crust, the scientists believe, is largely composed of bedrock rich in the mineral olivine. The team used the model to estimate the changes an olivine-rich rock might have undergone, assuming water had existed on the surface of Mars for at least two billion years, and the atmosphere was full of CO2.
"At this time in the history of Mars, we think that CO2 Found everywhere, in every corner, and the water seeping through the rocks is also full of CO2", said Marie.
For more than a billion years, water seeping through the crust slowly reacted with the olivine - the oxygen bonded to the iron, releasing hydrogen and forming the red oxidized iron that gives Mars its iconic color. The free hydrogen joined the CO2 in water and methane is formed. Over time the olivine turned into serpentine, also a rock rich in iron, which continued to react with water and smectite was formed.
More of the topic in Hayadan:
