Mars used to be a water-rich world before becoming the dry, cold desert that it is today. However, data from Curiosity previously revealed that the planet had flowing water for a lot longer than researchers expected. Now, a new theory suggests how that could have happened.
According to a study published in Nature Geoscience, explosive bursts of methane could have kept the Red Planet warm enough to allow liquid water on its surface. The international team of researchers developed a simulation to show that underground methane emissions could have extended Mars' capabilities to keep liquid water on its surface.
Being further away from the Sun, Mars has always been cooler than Earth. But for its first billion years of existence, it had a thick atmosphere that kept things stable. The constant erosion of the atmosphere by the solar wind led to the world we see today. This process should have been enough to make the planet waterless 3.6 billion years ago, but data from NASA’s Curiosity show that water persisted until about 3 billion years ago.
This epoch, called the Hesperian period, is a bit of a puzzle. Previous hypotheses like intense volcanism and meteor impacts could create climate warming episodes, but scientists were unsure if they would be enough for such a long-lasting event.
In Gale Crater, Curiosity has found evidence of flowing deltas and stable lakes throughout the Hesperian. It was possibly covered in ice, but it was a lake nonetheless. These findings motivated researchers to find a mechanism to keep Mars mild.
A key point in this study has to do with Mars’ wildly changing axis. Unlike Earth’s axis, Mars’ tilt can vary dramatically, even by 10 or 20 degrees. This can expose frozen regions of the planet previously at high latitudes to a warmer climate. The researchers think this could have allowed the surface ice to thaw and methane from the underlying rocks to erupt.
Methane is a terrifyingly efficient greenhouse gas, 25 times more powerful than carbon dioxide. It would take a very long time for methane to be broken down by sunlight. A methane-led warming of the Red Planet could have lasted for hundreds of thousands of years.
It’s still unclear what mechanism kept Mars warm during the Hesperian, and perhaps it wasn’t a single event but a combination of astronomical and geological events. The methane-burst hypothesis is an intriguing addition to the several ideas we currently have about early Mars.