Radar images near Mars’s south pole indicate liquid water beneath about 1.5 km of ice, according to a new study (Science 2018, DOI: 10.1126/science.aar7268). Roberto Orosei of the Italian National Institute for Astrophysics Data and colleagues observed a highly reflective, 20-km-wide region under the southern ice cap using a radar instrument on the Mars Express spacecraft. Similar signatures seen on Earth correspond to liquid water. Researchers first suggested there might be such lakes under martian ice caps more than 30 years ago. Previous estimates put the temperature under the ice cap at about –68 °C. The researchers suggest that perchlorate salts of magnesium, calcium, and sodium known to be in martian soil make the lake briny enough to stay liquid. The water or the ice nearby is a potential habitat for life, says study coauthor Elena Pettinelli of Roma Tre University. She adds that other such lakes may also exist on Mars. “This is a very encouraging and important result for the planetary science community and beyond,” says planetary geophysicist Essam Heggy of the University of Southern California, who wasn’t involved with the work.