New York, Aug 8 (IANS): Researchers have discovered evidence of an ancient lake on Mars that likely represents some of the last potentially habitable surface water ever to exist on the red planet.

Researchers at the University of Colorado at Boulder, examined an 18-square-mile chloride salt deposit in the planet's Meridiani region near the Mars Opportunity rover's landing site.

Large-scale salt deposits are considered to be evidence of evaporated bodies of water.

"This was a long-lived lake, and we were able to put a very good time boundary on its maximum age," said Brian Hynek, a research associate at the Laboratory for Atmospheric and Space Physics (LASP) at CU-Boulder and lead author of the study.

"We can be pretty certain that this is one of the last instances of a sizeable lake on Mars," Hynek emphsised.

Digital terrain mapping and mineralogical analysis of the features surrounding the deposit indicate that this one-time lake bed is no older than 3.6 billion years old, well after the time period when Mars is thought to have been warm enough to sustain large amounts of surface water planet-wide.

Planetary scientists believe that the solar system was formed approximately 4.6 billion years ago.

Based on the extent and thickness of the salt, the researchers estimate that the lake was only about eight percent as salty as the Earth's oceans and therefore may have been hospitable to microbial life.

"By salinity alone, it certainly seems as though this lake would have been habitable throughout much of its existence," Hynek dded.

The study was published in the journal, Geology.