Europe's Mars Express probe has revealed new insights into the history of water on the Red Planet. The work is key to understanding the likelihood of there having been life on Mars.
The findings, appearing in Science, are based on data from the orbiter's Omega spectrometer, which uses infrared and visible light to investigate geology. A team led by Jean-Pierre Bibring of the Institut d'Astrophysique Spatiale in Orsay, France, used mineral measurements to define three ages of the Martian environment.
The Phyllocian, the first of the three periods, was characterised by an abundance of clay-rich minerals, which would need plenty of alkaline liquid water to form. It lasted a relatively short time – from when the planet formed at the same time as Earth about 4.5bn years ago to 4bn years ago when Mars became significantly less hospitable.
The profusion of sulphate deposits marks the Theiikian era, and indicate volcanoes broke out like acne across the face of the adolescent planet. The huge quantities of sulphur dioxide the eruptions churned out mixed with the water on the surface, forming the basis for the sulphate deposits. This lasted for a billion years.
The final period, Siderikan, beginning 3.5bn years ago and lasting up to the present day, is less exciting. Mars became frigid, volcanically inactive, and most of the water disappeared. What remains is frozen at the poles. Slow formation of Mars' trademark red iron oxides was caused by peroxides in the thin atmosphere, the team say.
The researchers say future explorations of Mars' surface should aim for the oldest clay deposit regions as the chances of finding evidence of life are best here. NASA's Spirit and Opportunity rovers are in sulphate-rich areas from the middle era. Bibring told the BBC he hopes to put a minature version of Omega on the European Space Agency's exploratory 2011 ExoMars mission.
He said: “We will look for samples that are rich in hydrated clays because we think that they are the most favourable to host, at a microscopic level, potential bio-relics." ®