Mars, the Red Planet, used to be the wet planet according to new data to be published in Science tomorrow. Researchers have found extensive indications of massive sedimentary deposits, geological evidence which, on earth, is firmly associated with water.
The photographs which clearly show the deposits were taken over the past months by a camera on board the Mars Global Surveyor satellite, in orbit around the planet for a year.
The researchers are looking at layers of rock which could have been formed up to 3.5 billion years ago. They are strikingly similar to the geological features seen on earth in places such as the Grand Canyon in the US where the Colorado River has cut deep into ancient rock displaying its layered structure.
On earth the layers are laid down by water over millions of years. They start as muddy sediment, dirt, dead creatures and rotted plant life that sink to the bottom of lakes and seas.
This material is deposited over millions of years, getting deeper and deeper, eventually compressing into a form of rock that records a planet's history through the ages. Astonishing pictures from the satellite clearly show these layers on the surface of Mars. They are scattered all around the planet suggesting that there was an extensive network of lakes and shallow seas.
"We see distinct, thick layers of rock within craters and other depressions for which a number of lines of evidence indicate that they may have formed in lakes or shallow seas," according to Dr Michael Malin, principal investigator for the Mars Orbiter Camera. "We have never before had this type of irrefutable evidence that sedimentary rocks are widespread on Mars."
Where there is water on earth there is also life - so the findings have those seeking early forms of Martian life on the edge of their swivel seats. The fossil finds which tell us about the dinosaurs and early human-like ancestors on earth are recovered from sedimentary layers.
The layers preserve the fossils but also help scientists to date them through a number of elaborate research techniques. "It is reasonable to look for evidence of past life on Mars in these remarkably similar sedimentary layers," Dr Malin said.
Some of the layers are as much as four kilometres thick, the researchers report in Science. They acknowledge that their findings will be particularly appealing news for the "Mars astrobiological community" who hope to find fossilised life there. "The pictures . . . in fact show exactly the types of materials in which the record of Martian life, if it ever existed, is most likely to be preserved," the authors said.
The evidence uncovered so far only suggests relatively small bodies of water. There are no signs of there having been global oceans as on earth.
The most likely picture for Mars in light of the findings, they said, was of a planet with a substantial atmosphere that was capable of sustaining liquid water. This would have been in its "early years", more than 3.5 billion years ago. The movement of this water was of sufficient volume to erode and push about "substantial amounts" of rock material and so expose the layering.
In more recent times Mars became a cold, arid place with little atmosphere and no sign of liquid water. A key question however was whether there were "climate excursions" - periods when liquid water could again persist and accumulate in the planet's many deep impact craters.
So what happened to all that water, assuming that it did exist? The researchers have no data that helps them answer the question most people would ask. All recent efforts to find water however have come to little or nothing. Scientists are sure there is some water up there, accumulating with frozen carbon dioxide at the poles during the Martian winters. Doubts remain about how much there is and how difficult it would be to recover it.
The hope is that some of the water seeped down into the soil to await later discovery by a manned mission to Mars. It could also have been lost to space however as the Martian atmosphere thinned and atmospheric pressure dropped, allowing it to vaporise and escape.