NASA's Opportunity rover appears to have reached another milestone in its amazing nine-year mission on Mars, it has been revealed.
According to scientists, the robot has been trundling over what they believe to be clay-bearing rocks on the edge of a wide bowl known as Endeavour Crater.
Clays are water-altered minerals, but very different to the ones seen by the rover so far on its travels.
Those previous minerals were in contact with acidic water; clays are formed in the presence of neutral water.
"What drives us to investigate the problem of water on Mars is the fact that water is a necessary condition for life; but there's water and there's water," the BBC quoted Prof Steve Squyres, Opportunity's principal investigator from Cornell University in Ithaca, New York, as saying.
"We've been seeing sulphate minerals from day one with this rover. These sulphates form under very acid conditions. And even though water was present, if it's that acid it would be very challenging as a place for life to take hold.
"However, if it's not acid, if it's the kind of water you can drink, it's the kind of water that's going to be more suitable for life; and that's what the clays point to," he said.
Since August 2011, it has been driving across the western rim of the 22km-wide Endeavour depression.
Opportunity is trying to understand the sequence of rocks at the crater which is likely to have been punched out of the ground by an asteroid more than three billion years ago.
As part of that study it has been surveying a mound the science team refers to as Matijevic Hill in honour of the late Jake Matijevic, a senior rover engineer.
The findings of the study were presented at the American Geophysical Union (AGU) Fall Meeting. (ANI)