Hopes for life on Mars undermined as probe finds no trace of oceans

Scientists have dismissed the theory that Mars was a warm, wet planet with a thick atmosphere and deep oceans, all necessary conditions for the evolution of life.

The Mars Global Surveyor spacecraft orbiting the planet has failed to find the chemical signature indicating the red planet once had large bodies of open water. The finding is a severe blow to researchers who believe primitive life may have thrived on Mars.

Planetary scientists from Arizona State University in Tempe analysed data from an instrument on the spacecraft designed to detect substances called carbonates, which form when carbon dioxide comes in to contact with minerals and water. The thermal emission spectrometer detected only trace amounts of carbonates, rather than the huge amounts expected if Mars had seas and oceans, the scientists write in the journal Science.

Professor Philip Christensen, the principal investigator, said: "We believe the relatively small amounts probably did not come from oceans, but from the atmosphere interacting directly with dust. Tiny amounts of water in Mars' atmosphere can interact with dust to form the small amounts of carbonate that we see.

"This seems to be the result of a thin atmosphere interacting with dust, not oceans interacting with the big, thick atmosphere that many people have thought once existed there," he added.

Mars is now a bitterly cold planet with a thin, carbon dioxide atmosphere that is unable to retain any heat or any water that may have existed. It would be impossible for life to exist on the surface of the planet, although deep, subterranean life is a distant possibility.

Things could have been very different three billion years ago when Mars was thought to have had vast oceans and a much thicker atmosphere. But this should have left behind huge deposits of carbonates. The fact that it hasn't "points to a cold, frozen, ice Mars that has probably always been that way, as opposed to a warm, humid, ocean Mars," Professor Christensen said.