https://www.cnn.com/2018/07/25/world/mars-subsurface-water-lake-evidence/index.html
A lake of liquid water has been detected by radar beneath the southern polar ice cap of Mars, according to a new study by Italian researchers from the Italian Space Agency, published Wednesday in the journal Science.
Those pulses reflected 29 sets of radar samples that created a map of drastic change in signal almost a mile below the surface. It stretched about 12.5 miles across and looked very similar to lakes that are found beneath Greenland and Antarctic ice sheets on Earth. The radar reflected the feature's brightness, signaling that it's water.
"We interpret this feature as a stable body of liquid water on Mars," the authors wrote in the study.
The study authors ruled out any other causes for this brightness.