Without liquid water, life is impossible. The search for life on other planets, therefore, is often guided by the search for water. Our nearest planetary neighbor, Mars, is currently too cold to play host to liquid water on its surface, but, according to a recent, partially DCO-funded, study, this may not always have been the case.
Many millions of years ago, Mars was volcanically active, spewing gases into its atmosphere. As this activity decreased over time, such degassing also decreased. Changes in atmospheric composition have profound consequences for a planet; in particular the amounts of the greenhouse gases carbon dioxide and methane can affect surface temperature. Surface temperature, in turn, affects the behavior of all other compounds on the planet, including water.
Therefore, in order to understand the conditions of a young Mars (or indeed any other terrestrial planet), we need to understand volcanic degassing and how it is impacted by the chemical composition of the mantle.
In the present study, scientists from Brown University, Northwestern University, and the Carnegie Institution of Washington performed experiments on primitive magma analogs to understand how much carbon and water can be carried by magmas as they ascend and erupt. Their work, published in Proceedings of the National Academy of Sciences, challenges previous understanding of how carbon cycles in and out of the mantle.
Carbon moves through the mantle by interacting with other elements and compounds therein. A particularly important factor in deep carbon chemistry is the oxygen fugacity of molten rock, a metric that describes the abundance of reactive oxygen, and has been estimated for several terrestrial bodies in our solar system (including Mercury, Mars, and the Moon). The oxygen fugacity on Earth is higher than on other planets, but precisely how this difference affects volcanic degassing and therefore atmospheric composition was in question.
By studying various basaltic rock compositions, the authors showed that carbon is more soluble than previously thought in low oxygen fugacity situations. This discovery has implications not only for how we view the deep carbon cycle here on Earth, but how we view the history of a planet like Mars. The low oxygen fugacity there had led scientists to believe that, despite high levels of volcanic activity, Mars would never have been warm enough for liquid water to flow on its surface. Now, however, it would seem that this is not the case. Degassing of larger amounts of methane and carbon monoxide, and relatively less carbon dioxide, than predicted by prior models. Because methane has a stronger greenhouse effect than carbon dioxide, volcanic degassing could have produced a thinner atmosphere yet one more capable of warming the planet.
Photo Credit: NASA
A commentary was also published alongside the article in PNAS by DCO scientist Marc Hirschman.