Space scientists have, for the first time, discovered a lake of liquid water on Mars, raising hopes of martian life. The 20 km wide reservoir lies underground, about 1.5 km beneath the red planet’s south polar region. 

It was detected using ground-penetrating radar aboard a European spacecraft, Mars Express, that has been orbiting Mars since 2003.

An international team of scientists used the probe’s MARSIS instrument (the Mars Advanced Radar for Subsurface and Ionospheric Sounding) to survey the ice caps around Mars’ south pole.

They got their first clues to the Mars lake’s existence way back in 2012 and have been studying the area ever since when Mars Express flew over the site.

Signals that reflected back from a region called Planum Australe matched those detected from lakes of liquid water found beneath ice sheets in Greenland and Antarctica on Earth.

Professor Roberto Orosei, of the Italian National Institute for Astrophysics, who led the discovery team, said: “This subsurface anomaly on Mars has radar properties matching water or water-rich sediments.

“This is just one small study area. It is an exciting prospect to think there could be more of these underground pockets of water elsewhere, yet to be discovered.”

The scientists suggest that the water must be very salty, like a brine, to remain liquid in such cold conditions. This would make the Mars lake inhospitable for Earthlike microbial life.

But it raises hopes that more reservoirs of water could exist in other locations more favourable for life to exist, at more temperate latitudes.

The scientists’ study, published in the journal Science, concludes: “There is no reason to conclude that the presence of subsurface water on Mars is limited to a single location.

There is already overwhelming evidence that the red planet was once awash with water and that vast oceans covered Mars billions of years ago.

NASA has previously announced the discovery of seasonal flows of liquid water down crater walls on Mars, though subsequent studies have suggested they may actually have been dusty landslides.

Related: Guide to Mars