A Big Slab of Buried Ice at Utopia Planitia

Even though Mars' Utopia Planitia is at mid-latitudes, they can detect a significant slab of water ice buried there - enough to fill Lake Superior:

It was found using a radar mapper on MRO. Called SHARAD, it sends pings of radar down to the surface, which are reflected back up to the satellite and recorded. Different substances reflect radar differently; the rocks on the surface aren’t particularly good at it, which is why the radar can penetrate the ground. Water, on the other hand, reflects radar quite well, so SHARAD can detect water ice down to a depth of a kilometer below the Martian surface.

Scientists focused their attention on a region in Utopia Planitia that features lots of odd, scalloped terrain (aresain?), which is similar to places on Earth in the Arctic that have underground ice. Combining the data from over 600 MRO passes indicates how much ice there is. The area of the ice deposit is over 300,000 square kilometers and the thickness ranges from 80 to 170 meters. So yeah, that’s a goodly supply of ice.