The Mars Reconnaissance Orbiter has discovered a massive sheet of ice on Utopia Planitia, the same area where Viking landed in 1976. The ice sheet, buried under the soil, is nearly the size of New Mexico, according to Kenneth Chang at the New York Times.
The ice sheet ranges from 260 to 560 feet thick and researchers believe it is about half water with dirt, rocks, and empty spaces mixed in. Cassie Stuurman, lead author of the article in the journal Geophysical Research Letters, said in an interview with the New York Times that based on how the ice was deposited, it likely gathered through snowfall and was later buried. It does not appear there are any signs of it having ever melted into a lake.
Scientists have been interested in this area for a while because of polygonal cracking and scalloped depressions. Places on Earth often show patterns like these due to ice below expanding, contracting, and melting due to changing temperatures, causing the cracks and scallops.
This discovery, along with a more moderate climate than polar areas that have water deposits, may make Utopia Planitia a first choice for future landing sites if crewed exploration of the red planet goes forward.