Cirrus Clouds Could Have Kept Early Mars Warm, Scientists Say

A new study suggests that liquid water on Mars could have been caused by cirrus clouds.

According to researchers from the Carl Sagan Institute, cirrus clouds might have provided the needed warming for liquid water to flow in the planet.

"Our calculations indicate that cirrus cloud decks could have produced global mean surface temperatures above freezing, but only if cirrus cloud cover approaches ~75 - 100% and if other cloud properties (e.g., height, optical depth, particle size) are chosen favorably," the researchers wrote in the paper, which was published in arxiv.

Features such as the Valles Marineris are pointing to the possible existence of liquid water in early Mars, and that water had played an essential role in shaping the planet.

Previous studies linked these features to volcanic origins. But researchers Ramses Ramirez and James Kasting suggested that the warming had been caused by cirrus clouds - the same wispy clouds that appear on Earth, and created a climate model to test their theory.

Cirrus clouds have also been seen on Jupiter, Saturn, Uranus, and possibly Neptune. Ice crystals produced by cirrus clouds tend to evaporate before reaching the surface as they warm the air by 10 degrees Celsius, Universe Today reports.

On Earth, cirrus clouds have a heating effect, as they let the sunlight in but absorb infrared radiation coming out. According to the researchers, if Mars had been covered enough by cirrus clouds just like Earth, the clouds' heating effect might have warmed the planet enough to allow liquid water to flow.

Moreover, the researchers also suggested that comets and asteroids impacting the surface of the planet could also be responsible for the heat, and cirrus clouds might have trapped the heat in Mars' atmosphere.

Using the single-column radiative-convective climate model and simulating the conditions on Mars, the scientists found that while cirrus clouds could cover early Mars four to five times longer than Earth under the right circumstances, 75 to 100 percent of the planet would have to be covered. But the researchers said that the amount of coverage is unlikely.

Adjusting the parameters to 50 percent, similar to Earth's cloud cover, reduced the heating effect of the clouds and would not have been enough to warm liquid water.

However, the researchers also pointed that warming by cirrus clouds is possible if ancient Mars had a mean surface temperature lower than the 273 Kelvin in their model and that it would only have to be lower by 8 degrees Kelvin to make that happen.