Mars’ atmosphere is just 1 percent as dense as our own, but researchers believe that it was once a much warmer and wetter planet. According to a report from Phys.org, a recent study from Caltech offers insight into what may have happened to the atmosphere on Mars.

Mars’ thin atmosphere prevents large bodies of water from evaporating and subliming, which would set the formation of a more Earth-like atmosphere in motion. Scientists believe that Mars’ atmosphere was even thicker than that of Earth’s, and was primarily made of carbon.

A team of scientists led by Renyu Hu, a JPL postdoc and visitor at the planetary science department at Caltech have published their findings in the journal Nature Communications. According to Hu, the team has identified a new photochemical process that may have kick-started the dissipation of Mars’ early atmosphere without having ‘missing” carbon. “With this new mechanism, everything that we know about the Martian atmosphere can now be pieced together into a consistent picture of its evolution,” Hu said.

There are two possible ways that carbon could have exited the Martian atmosphere. In one explanation, atmospheric carbon dioxide was incorporated back into minerals and rocks called carbonates; in the second, it simply was lost to space.

Separate studies examining the carbonate rocks on Mars suggest that there are not enough minerals to have accounted for the entire atmosphere, which was at its thickest point roughly 3.8 billion years ago.

By comparing the relative abundance of carbon-12 and carbon-13 isotopes in the atmosphere, scientists may be able to piece together when the atmosphere started to dissipate into space. They compared measurements of the isotope ration in meteorites from Mars that contained gases from deep inside the planet’s crust. These offered a glimpse at what the chemical makeup of the earlier atmosphere on Mars was probably like.

The study has shed new light into the untimely fate of Mars’ once-rich atmosphere. A press release from Caltech outlining the details of the study can be found here.