The hope of discovering, or sustaining, life on Mars has received a major boost by the unexpected discovery of a huge 20km-wide lake of liquid water beneath the planet’s surface.
Dissolved salts are thought to keep the water fluid, despite having a temperature below freezing point.
The discovery below Mars’ southern ice cap, which has important implications for the chances of life surviving on the Red Planet, was made by an orbiting European probe using ground-penetrating radar.
It is the first time a large stable body of liquid water has been confirmed to exist on Mars. The lake lies about 1.5km below the surface of a region called Planum Australe, close to the Martian south pole, and stretches out for 20km.
Previous research found possible signs of liquid water flowing on the martian surface in the past, but this is the first sign of a persistent body of water on the planet in the present day.
Lake beds explored by Nasa’s Curiosity rover showed water was once present on the surface of Mars, however, the planet’s climate has since cooled leaving most of its water locked up in ice.
With surface temperatures as low as minus 68C, it would not exist as a liquid under normal conditions, but dissolved salts of magnesium, calcium, and sodium – present in Martian rocks – are thought to maintain the briny miniature sea by reducing the melting point of water to minus 74C.
An Italian team of scientists detected the lake while carrying out a radar survey using the Mars Express spacecraft.
Between 2012 and December 2015 the Planum Australe region was mapped by the Mars Advance Radar for Subsurface and Ionosphere Sounding (Marsis) instrument carried on the orbiter.
Radar instruments like Marsis examined the surface and immediate subsurface of the planet by sending out a signal and examining what is bounced back.
Beneath an accumulation of water ice and dust, researchers spotted something unusual 1.5km under the ice.
They revealed the presence of liquid water. ”Anomalously bright subsurface reflections are evident within a well-defined 20km-wide zone, which is surrounded by much less reflective areas,” Professor Roberto Orosei, from the University of Bologna, wrote in the journal Science.
“Quantitative analysis of the radar signals shows that this bright feature has high relative dielectric permittivity (electrical polarisation) matching that of water-bearing materials.
“We interpret this feature as a stable body of liquid water on Mars.” The discovery greatly increases the chances of extraterrestrial life existing on Mars, which billions of years ago, is thought to have had oceans and rivers, much like Earth.
If large bodies of liquid water lie beneath Martian polar ice, they could theoretically harbour living microbes to this day.