Not a lot is known about Mars and what appears to be known – like liquid water on its surfaces – is now in contention according to a new study.
When NASA proclaimed in September there could be life, or at least water, on Mars a la David Bowie it was one of the biggest breakthroughs they'd had about the red planet.
Even overnight, NASA's Curiosity Rover found much higher concentrations of silica which indicates "considerable water activity".
But new research from US and French scientists have perhaps put that theory on ice, suggesting the small sloping gullies on Mars were carved out by defrosting carbon dioxide ice rather than flowing water.
The study, published in Nature Geoscience today, suggests the Martian gullies may look like those formed on Earth but the process may have been very different.
The authors believe the surface around the gullies is too cold to harbour large volumes of liquid water.
"The gullies are less than a few million years old — with some actively forming today—and seasonally active on slopes during times that coincide with defrosting carbon dioxide ice on the Martian surface, indicating that dry ice may be involved in their formation," the study says.
Cedric Pilorget and François Forget from Université Paris-Sud, France suggest as a layer of CO2 ice which coats a sloped surface defrosts, trapped CO2 gas builds up beneath the ice layer and eventually destabilising the soil and producing a flow of gas and debris.