One of Nasa's Mars rovers has discovered convincing chemical evidence that the area it is exploring was once covered with water.

One of Nasa’s Mars rovers has discovered convincing chemical evidence that the area it is exploring was once covered with water, meaning that Mars could once have been hospitable to life.

One of the main tasks of Nasa’s two Mars rovers is to look for minerals that may have been formed through the activity of water (see Chem. Br., December 2003, p15). It is these minerals that one of the rovers, Opportunity, has now discovered in an outcrop of rock near where it landed.

Using its X-ray spectrometer, Opportunity has detected a high concentration of sulphate salts in the rocks, as well as evidence for the presence of chloride and bromide salts, while with its M?ssbauer spectrometer it has detected a hydrated iron sulphate mineral called jarosite. On Earth, rocks containing these salts have either formed in water or been exposed to water for long periods of time. In addition, the rocks possess distinctive marks and layers that also point to them having been exposed to water.

This wide variety of evidence has made Nasa very confident of its assessment. ’Liquid water once flowed through these rocks,’ asserts Steve Squyres of Cornell University, New York, US, and the mission’s principal scientific investigator. ’It changed their texture and it changed their chemistry.’

Opportunity will now further examine the rocks to try to determine whether they could have been formed by minerals precipitating out of solution at the bottom of a salty lake or sea.

Jon Evans