A Little Methane and Hydrogen May Have Kept Mars Warm

A growing number of studies have pointed to the existence of liquid water on Mars. Since the 1970s, scientists have hypothesized that the chilly Red Planet must have once been warm enough to allow water to flow on its surface. NASA's Curiosity rover was sent to Mars primarily to investigate possible liquid water sites on the Red Planet.

But scientists are still struggling to explain how a planet that is so far away from the sun could have gotten warm, especially during the sun's dim phase - a time when it was 10 to 15 percent dimmer than it is today.

The thin Martian atmosphere is now mostly carbon dioxide. According to climate models, carbon dioxide - a type of greenhouse gas - could trap little heat and would not have kept Martian temperatures high above freezing levels when the sun was fainter.

But a new study by Robin Wordsworth of Harvard University suggests that even if just a few percent of carbon dioxide in the atmosphere is made up of molecules of hydrogen or methane - about 2 to 10 percent - it could be enough to keep the planet warm. According to Wordsworth, when hydrogen or methane collide with carbon dioxide molecules, they absorb light in a key wavelength range and allows the planet to trap enough heat to let the water flow, New Scientists reports.

A previous study by James Kasting of Pennsylvania State University had introduced a climate model that involves a bigger percentage of hydrogen. According to Kasting and his colleagues, a few percentage of carbon dioxide in addition to 5 to 20 percent hydrogen could have been needed to keep the Red Planet warm.

"We had to wave our arms a lot to justify that much hydrogen in the atmosphere," Kasting told New Scientist. "This new paper allows that same hypothesis to work with a lot less arm waving."