Thanks to erosion wearing away surface rock on Mars, scientists using NASA’s Mars Reconnaissance Orbiter have spotted thick deposits of ice in the planet’s mid-latitudes that extend hundreds of feet deep.

The discovery, described in the journal Science, could offer researchers a tantalizing new spot to sample our dusty, rusty neighbor.

“This ice is a critical target for science and exploration: it affects modern geomorphology, is expected to preserve a record of climate history, influences the planet’s habitability, and may be a potential resource for future exploration,” the study authors wrote.

In spite of its dry appearance, about a third of the Red Planet actually holds shallow ground ice. But while that frozen water’s extent is fairly well known, other crucial details — how thick it is, what its layers look like, and how pure it is — largely remain unknown. If future explorers want to be able to draw down these water sources, scientists are going to have to learn much more about them.

The deposits described in this new paper offer a potential window into some of those mysteries. The researchers examined eight different exposed ice deposits on the planet spotted by the orbiter’s HiRISE camera. Seven of them are pole-facing scarps (that is, steep banks or slopes) in the southern hemisphere; one is a cluster of scarps in the northern hemisphere, in Milankovic Crater.

“The scarps are sharply defined and nearly straight, up to (about 3.7 miles) long, and face slightly east of poleward,” the scientists wrote.

These ice deposits could start just 1 to 2 meters beneath the surface but extend more than 100 meters (or more than 328 feet) deep. They’re capped with a layer of rock and dust that’s been cemented with ice. These deposits seem to be pretty pure in terms of composition — not a lot of dust or dirt mixed in — which was not what scientists originally expected.