Where Did the Carbon in the Martian Atmosphere Go?

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Where did the carbon in the martian atmosphere go? This puzzling question has troubled scientists for a long while. Now a joint scientific team from the California Institute of Technology and JPL believe they found the answer.

Mars is covered by a thin atmosphere, mostly composed of carbon dioxide. The martian atmosphere is so thin that it cannot prevent surface water from evaporating. However, it’s been long thought the atmosphere of Mars was once far thicker than even that of Earth. In line with this hypothesis, the joint scientific team suggests that Mars was indeed blanketed by a thicker atmosphere 3.8 billion years ago.

The study published in the Nature Communications journal presents a plausible scenario where a photochemical process led to the thinning of the atmosphere while being consistent with the current carbon stock and eliminating the possibility of carbon having escaped in space.

According to the joint scientific team, two possible scenarios related to the thinning of the martian atmosphere can be taken into account. The first is that the excess carbon dioxide was lost in space. The second and the start point of the California Institute of Technology-JPL research is that the excess carbon dioxide was stocked in minerals found in rocks. The rocks on the surface of Mars are called carbonates.

A JPL study involving crunching data from several satellites orbiting the red planet has yielded a great study resource: an inventory of carbonates on Mars. According to this study, the upper crust of the red planet doesn’t contain sufficient carbonates to account for the thinning of the martian atmosphere by stocking carbon 3.8 million years ago.

So where did the carbon in the martian atmosphere go? Another piece of the puzzle was set in place when the researchers analyzed carbon isotopes ratio (carbon-12, carbon-13) to study the escape-to-space hypothesis. The carbon isotope ratio at different points in time acts as an accurate indicator of the timeline of the thinning of the martian atmosphere.

The start point for the measurement was established by measuring the carbon isotope ratio  of martian meteorites. These contain gases consistent with the deep mantle of the red planet. The atmosphere of a planet is produced as the mantle releases gases via volcanic activity. As such, the starting point is a measure of the initial martian atmosphere.

The results obtained were compared to the carbon isotopes of the martian atmosphere as collected by Curiosity. The isotopic measurements of Curiosity reveal that the martian atmosphere is rich in carbon-13. If the carbon had escaped to space, carbon-12 isotopes would be the first to reach the atmosphere and escape as they are lighter.

However, a photochemical process might have intervened. An ultraviolet light particle would meet a carbon dioxide molecule in the upper atmosphere and divide it into carbon monoxide and oxygen. Another ultraviolet light particle encountering a carbon monoxide molecule divides it into carbon and oxygen. Carbon thus produced would have escaped the atmosphere.

Photo Credits: Phys.org