Ancient Martian Air 'Too Cold and Thin' for Liquid Water

The air on Mars 3.6 billion years ago was too cold and thin for liquid water to form, scientists have said.

Nasa's Rover explorers had found evidence that water was present on the Red Planet in its liquid state billions of years ago and there was enough for rivers and lakes to exist.

However, research published in the journal Nature Geoscience suggests that water formation on Mars was the result of occasional warm spells

According to Nature magazine, researchers are increasingly finding evidence to suggest that Mars was not warm and wet during its early history, which would have required an atmosphere much thicker than modern times.

Edwin Kite, a planetary scientist from Princeton University, said it is very unlikely Mars was able to hold a thick atmosphere for more than a few thousand years at a time.

He said the size of the planet's craters provide evidence to support their theory. Using images from the Mars Reconnaissance Orbiter, the team catalogued over 300 craters over 84,000 square kilometres.

If Mars had a thicker atmosphere, small objects would have broken up as they passed through, like they do with Earth, rather than surviving intact to create big blast craters.

Only 10% of the craters had diameters of 50m or less, with many believed to be the remnants of ancient craters being 21m or smaller.

After using a computer model to look at a simulation of incoming objects striking Mars with different atmospheric densities, the researchers found it was probably no more than 150 times its current state. This means it was about a third as thick as it needed to be to host liquid water and consistently keep the surface temperature above freezing.

James Head, from Brown University in Rhode Island, said: "This is an excellent paper. It bolsters previous studies that suggest early Mars was icy."

Kite said the most likely scenario for water on Mars was the red planet being intermittently warm through greenhouse gasses from volcanic activity – enough to thicken the atmosphere for a few millennium: "That's plenty enough to get fluid flowing [on Mars]," he said.