Maybe Sulfur Dioxide, Not Carbon Dioxide, Kept Mars Warm

Try to walk on Mars today, and the planet will simultaneously freeze and suffocate you. Not to mention the minimal air pressure and relentless radiation from space. But billions of years ago, the Red Planet was much warmer and liquid water flowed on its surface. Warm temperatures on Earth are maintained by the carbon cycle, but maybe another greenhouse gas – sulfur dioxide (SO2) – maintained the temperatures on Mars.

This is the hypothesis put forward by Harvard and MIT researchers, published in the December 21st edition of the journal Science.

Over millions of years on Earth, our climate has been controlled by the carbon cycle. Carbon dioxide is released from volcanoes, and then chemical reactions with silicate rocks on the Earth’s surface remove it back out of the atmosphere and turn it into limestone.

There are vast deposits of limestone on Earth; evidence that the carbon cycle has been going on for eons. But planetary geologists haven’t found any limestone on Mars. If the planet was kept warm, the limestone should be there.

Perhaps another greenhouse gas, sulfur dioxide – also released in vast quantities from volcanoes – kept the atmosphere warm. On Earth, sulfur dioxide is removed quickly from the atmosphere, since it’s even more reactive with silicate rocks than carbon dioxide.

“The sulfur dioxide would essentially preempt the role of carbon dioxide in surface weathering reactions,” says Itay Halevy, the first author of the report. “The presence of even a small amount of sulfur dioxide in the atmosphere would contribute to the warmer climate, and also prevent limestone deposits from forming.”

So if this is true, sulfur minerals, and not limestone, should have formed in bodies of water. This may help to explain the surprising discovery the rovers have made that sulfur minerals are an abundant component of Martian soils.

With sulfur dioxide, the Martian oceans would have been much more acidic than Earth’s oceans. There might have been periods on Earth when our atmosphere was similar, and there could be similar periods when sulfur kept us warm too.

The similarities and differences of the two planets still have much to teach scientists.

Original Source: Harvard News Release