These holes, captured on Alaska's Matanuska Glacier in July 2012, are formed by cryoconite – dust particles that melt into the ice over time, eventually forming small pockets of water below the glacier's surface. Scientists believe similar pockets of water – called cryoconite holes on Earth – could form within dusty water ice on Mars. https://photojournal.jpl.nasa.gov/catalog/PIA26409

JPL engineer Andy Klesh lowers a robotic submersible into a moulin. Klesh and JPL's John Leichty used robots and probes to explore the Matanuska Glacier in Alaska this past July. Image Credit: NASA/JPL-Caltech