New Delhi: Mars may have liquid water close to the planet’s surface, according to the Curiosity rover of National Aeronautical Space Administration (Nasa).

“Liquid water is a requirement for life as we know it, and a target for Mars exploration missions," said Javier Martin-Torres of the Spanish Research Council and Lulea University of Technology, Sweden, and a member of Curiosity’s science team. “Conditions near the surface of present-day Mars are hardly favourable for microbial life as we know it, but the possibility for liquid brines on Mars has wider implications for habitability and geological water-related processes."

Torres is lead author of a study published on Monday in Nature journal.

Since Curiosity landed on Mars in a 154km-wide crater called Gale in 2012, it has travelled more than 10km from the landing site towards Mount Sharp and carried several studies.

The scientists discovered calcium perchlorate in the soil, which under the right conditions absorbs water vapour from the atmosphere. The measurements from Curiosity’s weather monitoring station show these conditions exist at night and just after sunrise in the winter.

Using measurements of humidity and temperature at the surface and atmosphere of the planet, scientists could approximately calculate the amount of water that is absorbed.

“When night falls, some of the water vapour in the atmosphere condenses on the planet surface as frost, but calcium perchlorate is very absorbent and it forms a brine with the water, so the freezing point is lowered and the frost can turn into a liquid," explains Morten Bo Madsen, associate professor and head of the Mars Group at the Niels Bohr Institute at the University of Copenhagen.

Bo Madsen further explained that the soil is porous, so the water seeps down through the soil.

Eventually, other salts can also dissolve in the soil and since they are now liquid, they can move elsewhere under the surface.

Mars probe’s stereo camera has earlier shown areas typical of old riverbed with rounded pebbles, which show that a long time ago there was flowing, running water with a depth of up to one metre. The new close-up images taken by the rover on its way to Mount Sharp show that there are stretches of sedimentary deposits, a hint that large amounts of water flowed down the crater.

“The sediment plates on the bottom are level, so everything indicates that the entire Gale Crater may have been a large lake," explains Bo Madsen.