(New Scientist) The idea that Mars was once a warm place, awash with oceans that could harboured early life has taken a knock – new data suggests it was always cold, frozen and probably lifeless.
A survey of the Red Planet’s surface has revealed only traces of carbonates, minerals that should have formed in abundant quantities if Mars once had expansive seas. On Earth, the mineral is found in limestone and chalk deposits around the world.
The data was collected by a thermal emission spectrometer (TES) on NASA’s Mars Global Surveyor and was analysed by researchers at Arizona State University in the US. The results confirm that the spacecraft’s sensing apparatus works.
“We found carbonate, but we’ve only trace amounts,” said team leader Philip Christensen. “This really points to a cold, frozen, icy Mars that has probably always been that way.”
“We believe that the relatively small amounts that we see probably did not come from oceans, but from the [carbon dioxide] atmosphere interacting directly with dust,” he said.
Mars Global Surveyor scanned the surface of the planet for six years, with a resolution of about three kilometres. An alternative explanation for why only trace amounts of carbonate were found is the rock is hidden beneath layers of surface dust or rock.
Christensen thinks this is unlikely. “We see so much erosion in canyons, and valleys and plains that have been stripped bare,” he said. “It seems unlikely that the carbonate rocks could all be hiding out of view. When you look at the entire planet, you’d think that somewhere a little piece would be exposed.”
But Ross Irwin, a geologist with the Smithsonian Institution, disagrees. “Lots of basins have been resurfaced on Mars,” he told the Associated Press. “Carbonate could be in the subsurface or buried beneath sediment. There could be extensive carbonate deposits that are difficult to locate.”
Irwin thinks the new finding does not rule out the possibility that Mars had seas or oceans. He argues that many topographic features, such as basins and river beds, were clearly carved by running water.