perfidy

That's what space.com is reporting, cautiously.

Opportunity rover sent back new images from Mars showing that small spheres previously found on the surface also exist below, in a trench the rover dug. Hints of salty water were also found in the trench, but much more analysis is needed to learn the true composition.

Meanwhile Opportunity's twin rover, Spirit, is about to dig a trench of its own in order to investigate soil that sticks to its wheels, suggesting the fine-grained material might be moist.
In a press conference today, officials said the soil at both locations could contain small amounts of water mixed with salt in a brine that can exist in liquid form at very low temperatures.

The scientists stressed that only miniscule amounts of water would be needed to create the brine.