How Mars Has Lost its Atmosphere

Today’s Martian atmosphere is tenuous.

There are two possible mechanisms that may explain how Mars transitioned to its current state. While this has been a viable theory, new results from NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) has shown that the solar wind wipes away around 100g of particles per second.

Essentially, in models in which Mars has a more Earth-like atmosphere, one large agent accounts for the loss of massive amounts of carbon.

Sputtering favors carbon-12 a bit more than carbon-13, but the difference is not enough to explain the ratio of carbon-12/carbon-13 in Mars’ atmosphere. And it continues to this day.

Scientists from Caltech and NASA’s JPL tackled the problem in a paper published this week.

This previously dense atmosphere that may have had a surface pressure similar to Earth’s, has evolved through time into a tenuous one. 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, as a starting point for the research, the team involved with the study used measurements of the carbon isotope ratio in martian meteorites that contain gases that originated deep in the planet’s mantle.

“Our paper shows that transitioning from a moderately dense atmosphere to the current thin one is entirely possible”. However until now there was no explanation for how did that change, transforming the planet into the cold, dry place that it is today. One reads the Carbon dioxide was absorbed into minerals in carbonates, a kind of rock.

A recent study rules out the carbonate scenario.

But scientists think still there should be more carbon in Modern Martian atmosphere. “Even if you combined all known carbon reservoirs together, it is still nowhere near enough to sequester the thick atmosphere that has been proposed for the time when there were rivers flowing on the Martian surface”.

The escaped-to-space scenario has also been problematic. This process involves interactions between solar wind and the red planet’s upper atmosphere.

Hu and the team based their findings on data collected by NASA’s Curiosity robotic rover and orbital satellites. But not in substantial amounts.

To verify the theory of the carbon dioxide being lost in space, scientists start measuring carbon-12 and carbon-13.

So what’s going on? It’s called ultraviolet photodissociation. Another ultraviolet light particle encountering a carbon monoxide molecule divides it into carbon and oxygen. The ratio of carbon isotopes is then affected as carbon atoms are lost the space. Scientists found that carbon-12 was much more likely to escape than carbon-13. The infographic below visualizes this process.

Modeling the long-term effects of this ultraviolet photodissociation mechanism coupled with volcanic gas release, loss via sputtering, and loss to carbonate rock formation, the researchers found that it was very efficient in terms of enriching carbon-13 in the atmosphere.

It’s nearly a given now that, 3.9 billion years ago, Mars had lakes of water on its surface.

“This solves a long-standing paradox”, said Bethany Ehlmann of Caltech and JPL, a co-author of study. This could help in determining mass of the carbon. “You can use normal loss processes as we understand them, with detected amounts of carbonate, and find an evolutionary scenario for Mars that makes sense”.