Rough Guide to Mars
Virtual geology: a 3D model of Ophir Chasma, Mars, from Mars Express stereo images © FUB/ESA
The identification of a huge frozen sea on Mars has significantly increased the odds of recent or continued life on the planet. John Murray of the Open University, and Jan-Peter Muller of University College London identified the sea from stunning images taken by the High Resolution Stereo Camera on board the European Space Agency's Mars Express spacecraft. 'When I first saw the image I immediately thought of pack ice,' says John. 'The more we studied it the more convinced we became that this was ice and not volcanic lava.'
It is not clear whether the actual ice still exists on Mars or whether the images are purely the patterns of dust and rock that the frozen sea would have created. John explains, 'Ice is unstable at the surface of Mars because of the low atmospheric pressure, it sublimates away, in other words changes straight from ice to vapour without passing through the liquid state'. But two observations have led John and others to suggest that in this case ice still exists, possibly protected from sublimation by layers of volcanic dust. Firstly, the submerged craters are too shallow, indicating that most of the ice is still in the craters; and secondly, the surface is too flat if the ice had been lost there would be a greater height variation.
'What is particularly outstanding about this frozen sea is its age. The ice formed only five million years ago, which in geological terms is like yesterday,' explains John. 'If water has been forming ice on Mars throughout its history, and as recently as five million years ago, it is almost certain that water still exists somewhere on Mars.'
'The age of the frozen sea was measured by studying the numbers of crater impacts on the surface. This is a standard technique for dating geological features of planets. It's like leaving a piece of paper outside in the rain,' says John. 'The longer it is out there the more rain falls on it. Mars' frozen sea has relatively few impacts and is therefore not that old.'
'The new images suggest the frozen sea formed from water that erupted at great pressure as fountains from a series of deep fissures that tapped into reserves of warm water a few kilometres below the surface of Mars. We are talking about almost unthinkable amounts of water,' says John. 'The frozen sea this flood created is about the same size and depth as the North Sea.'
Clearly the presence of this frozen sea has provided the best evidence yet that life could have developed and may even still exist on Mars.