Mars
Mars used to host vast oceans and rushing rivers on its surface, but most of that water is now gone, lost to outer space. Some water still exists on Mars today, but it’s practically all ice. As research from 2018 showed, however, some stable liquid water may exist near the Red Planet’s south polar ice cap.
An instrument aboard the Mars Express spacecraft bounced radar off the Martian surface, showing an odd subterranean structure measuring 12 miles (20 km) across. Its physical properties led Italian scientists to propose the presence of liquid water, which likely exists as a brine pool or sludge filled with soil. This is potentially good news for future Martian explorers, as liquid water will be a scarce commodity on the Red Planet.
