Found it! Ice on Mars NASA Science

Using instruments on NASA’s 2001 Mars Odyssey spacecraft, surprised scientists have found enormous quantities of buried treasure lying just under the surface of Mars — enough water ice to fill Lake Michigan twice over. And that may be only the tip of the iceberg. “This is really amazing,” says William Boynton of the University of Arizona. “This is the best direct evidence we have of subsurface water ice on Mars.” Indeed, he added, “what we have found is much more ice than we ever expected.” “It may be better to characterize this layer as dirty ice rather than as dirt containing ice,” notes Boynton. The amount of hydrogen detected corresponds to 20% to 50% ice by mass in the lower layer. Because rock has a greater density than ice, this amount is more than 50 percent water ice by volume. This means that if one heated a full bucket of this ice-rich polar soil it would result in more than half a bucket of liquid water.