The first large, stable mass of liquid water has been detected on Mars - boosting the chance of one day finding life on the planet.

Scientists using ground-penetrating radar found a 12-mile (about 20km) wide lake about a mile beneath the southern ice cap.

Salts in the lake are believed to have kept the water - which has a temperature as low as -68C (-90F) - from freezing over.

Liquid water is an essential requirement for life as we understand it.

Conditions in the lake may be harsh - and not suitable for fish or complex organisms - but it is possible some microbes may be able to survive.


The fact that it exists raises the prospect of other liquid water that could be warmer and less salty.

The lake's depth is not known however, and scientists say it could be very shallow and murky.

Mars is now cold and dry but dried-out lake beds and river valleys point to an abundance of water more than three billion years ago.

There has also been evidence of recent water activity - such as long, dark streaks appearing on steep slopes - but never of stable bodies of water.

Image: Mars is barren - but billions of years ago there was an abundance of water

An Italian team discovered the lake while analysing a radar survey that was done between 2012 and 2015 by the Mars Express orbiter spacecraft.

One of the 29 samples showed unusually strong reflections.

Professor Roberto Orosei, from the University of Bologna, wrote in the journal Science: "Anomalously bright subsurface reflections are evident within a well-defined 20-kilometre-wide zone ... which is surrounded by much less reflective areas."

He said further analysis led them to "interpret this feature as a stable body of liquid water on Mars".

"It's tempting to think that this is the first candidate place where life could persist [on Mars]," said Prof Orosei.

The tool used to detect the water is called the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS).

It sends pulses that can penetrate the planet's ice caps and give an indication of what is below the surface.

Researchers said it could take years to verify whether something is actually living in this body of water. Still the discovery generated excitement among many experts.

Image: The InSight lander is due to land on Mars in November. Pic: NASA

Alan Duffy, an associate professor at Swinburne University in Australia, said: "This is a stunning result that suggests water on Mars is not a temporary trickle like previous discoveries but a persistent body of water that provides the conditions for life for extended periods of time."

Scott Hubbard, a professor of astronautics at Stanford University who served as NASA's first Mars program director in 2000, called the discovery "tremendously exciting".

Another spacecraft, the InSight Mars lander, was launched in May and will dig under the planet's surface after it lands in November.