Ancient water: Channels scoured by ancient outbursts of flood waters are seen in this orbital view from Mars Odyssey's Thermal Emission Imaging System. The features are billions of years old.

Credit: NASA/JPL-Caltech/ASU

The results also show that while water was present on Mars in the past in large quantities, it was there only briefly and intermittently. Water on Mars was more acidic than rainwater on Earth, and rocks would have weathered – altered from exposure to rain and wind – more quickly than they do on Earth.

However, chemical analysis of the rocks show little trace of alteration by water, nor is there any sign of large expanses of chlorine that would have been left by a hypothetical northern sea.

Water everywhere, but only briefly

Huge drainage channels leading from the southern hemisphere of Mars into the northern plains indicate there was a rapid outflow of water, leading scientists to postulate the presence of the sea. However, Taylor says such events must have been short, intense outbursts.

"The water story is very mysterious and something we don't know enough about," said Taylor. "Even if water was extensive, it didn't leave a big geochemical signal at the surface."

Andrew Prentice, a mathematician from the Centre for Stellar and Planetary Astrophysics at Monash University in Melbourne, who is presenting his own theory of Solar System formation at the conference, said Taylor's research sounds "very reasonable." He added that it fits with his theory that the Solar System formed from a nebula with a compositional gradient rather than planetary collisions.

"Planets formed where we see them today and retained the chemistry appropriate to their distance from the Sun," said Prentice. "This result is in sharp variance with the predictions of the accepted disc model of Solar System formation, where widespread radial mixing [and collisions] destroyed the compositional gradient and made all planets the same bulk composition."