"We're now seeing geological characteristics on Mars that could be related to life," said James Head of Brown University in Rhode Island and an author of one of the papers. "But we're a long way from knowing that life does indeed exist."

The new evidence, based on images of the planet's surface from the High Resolution Stereo Camera (HRSC), shows Mars is dynamic and had a watery past. Liquid water is seen as a prerequisite for earthly life.

Ernst Hauber, of the German Aerospace Centre in Berlin, and his colleagues said eruptions that occurred 350 million years ago made depressions on the Hecates Tholus volcano. Five million years ago glacial deposits formed inside the depressions.

Head and his team said glaciers on the planet moved from the poles towards mid-latitude regions 350,000 to four million years ago.

In the final research paper, John Murray of the Open University in Britain reported evidence of a frozen body of water, about the size and depth of the North Sea.

The HRSC evidence suggests the water is still there as ice on the ground or deep below the surface.

Head said the glacial deposits that his team studied could be sampled in future space missions and may provide more data about life on the planet.