http://www.newscientistspace.com/article/dn8397--radar-reveals-ice-deep-below-martian-surface.html

Ice bowl
Johnson and colleagues have now revealed subsurface measurements of two regions in the planet's northern hemisphere – the mid-latitude lowlands called Chryse Planitia and the northern polar cap.

They believe a 250-kilometre-wide circular structure that lies between 1.5 and 2.5 kilometres below the surface of Chryse Planitia is an impact crater that was buried with volcanic ash or soil several billion years ago. The team sees no radar boundaries in material that fills the bowl of the crater and the radar signals lose little strength when passing through it. That suggests the infill must contain a large proportion of ice, which is nearly transparent to radar.

Substantial amounts of ice in the soil would make sense given the crater's location in what appears to be a basin where ancient rivers once converged. "If the water could be captured in a basin and preserved for several billion years, it may still be there," says Plaut.

Intriguingly, the signal reflected from the bottom of the crater is so strong and appears so flat that it may be liquid water. "If you put water there, that's what the signal might look like," Johnson told New Scientist. But he cautions the data is based on only one pass over the region and could be caused by another material.

The rest of the article indicated how very little of Mars has been examined by Marsis yet. Let's not all pat Nick on the back yet.