Mars' carbon mysteriously disappeared, and scientists now know why

A team of scientists, trying to track down the 'missing' carbon from the Martian atmosphere, has come up with an answer.

Mars is blanketed by a thin, mostly carbon dioxide atmosphere, one that is far too thin to prevent large amounts of water on the surface of the planet from subliming or evaporating. But many researchers have suggested that the planet was once shrouded in an atmosphere many times thicker than Earth's. For decades that left the question, "Where did all the carbon go?"

The Caltech and JPL researchers suggest that 3.8 billion years ago, Mars might have had only a moderately dense atmosphere. They have identified a photochemical process that could have helped such an early atmosphere evolve into the current thin one without creating the problem of "missing" carbon and in a way that is consistent with existing carbon isotopic measurements.

With this new mechanism, everything that researchers know about the Martian atmosphere can now be pieced together into a consistent picture of its evolution, says lead author Renyu Hu. When considering how the early Martian atmosphere might have transitioned to its current state, there are two possible mechanisms for the removal of excess carbon dioxide (CO2). Either the CO2 was incorporated into minerals in rocks called carbonates or it was lost to space.

The complete study appears in the journal Nature Communications.