Wednesday, October 14, 1998 Published at 00:57 GMT 01:57 UK
Mars' violent past revealed
Olympus Mons: Extinct volcano and scene of past violence
By our science editor David Whitehouse
Flash floods unlike anything seen on Earth may have once ravaged the surface of Mars, according to new data.
The Mars Global Surveyor spacecraft, in orbit around the red planet for more than a year, has sent back images that show just how violent some periods in Mars' past may have been.
Imagine a large asteroid striking Mars, gouging out a crater a hundred miles across. The heat from the impact would melt rock and release water trapped beneath the surface.
Huge boulders would be carried hundreds of miles across Mars and dumped when the water lost its energy.
Scientists estimate that the ferocity of these floods was at least a thousand times greater than the floods that have devastated the American mid-west in recent years.
As the water reaches the plains it becomes a mudflow and either seeps back into the Martian surface or evaporates into space.
Winds reach 350mph
This is the dramatic picture of Mars' past outlined by astronomers at this week's meeting of the planetary science division of the American Astronomical Society.
John Pearl, of Nasa, said: "Mars is a small planet that does things in a big way." MGS images are showing this to be the case.
In addition MGS has provided new data about present day storms on Mars, which can reach windspeeds of 350mph.
Scientists believe that the energy for these violent storms comes from dust in the atmosphere.
It is possible that dust near the ground absorbs heat from the sun and releases that energy when high in the atmosphere. This could cause vortex motions that grow to become planet-wide storms.