This is the kind of discovery we have been dreaming of for decades. Data from the European Space Agency's Mars Express orbiter has provided compelling evidence for a massive, 20-kilometre-wide subglacial lake of liquid water sitting deep beneath the Martian southern polar ice cap.



Because the temperatures are so low, the water must be incredibly briny (salty) to remain in a liquid state. Nevertheless, on Earth, subglacial lakes like Vostok in Antarctica are known to harbour microbial life. Finding a stable, long-term body of liquid water on Mars drastically changes the landscape of our search for extraterrestrial life within our own solar system.