It’s the Holy Grail of the Mars mission — and it may be hiding in an ancient lake bed on the surface of the Red Planet.

The search continues for signs that life once existed on Mars, with some hints but no confirmed success yet from the Mars Opportunity or Curiosity rovers currently on the planet’s surface — but the discovery of an orbiting spacecraft of a spot 100 miles from one of the rovers could hold the key, according to an AOL report.

A new study indicates that salt deposits were found in an ancient lake that may have been home to the last living organisms to survive on the planet. Any water that was there would have to have been about 3.6 billion years old, which is actually about 200 million years more recent than previous estimates of the last time water was thought to have existed on Mars.

Scientists believe that the water at that point receded and froze at the poles when Mars became colder and had less atmospheric pressure.

The lead author of the study, research associate Brian Hynek at the Laboratory for Atmospheric and Space Physics at CU-Boulder, said that have water at a later time on Mars increases the likelihood that life once existed, because it means there was more time for it to have developed.

There are other signs that are good: the salinity levels most likely would have been about 8 percent of the level found in the oceans here on Earth, which is well within the range it would take to sustain life.

This 18-square-mile lake bed — basically an expanse of chloride — can be found in the Meridiani area, which is about 100 miles from where the Mars Opportunity rover landed years ago. However, at that range, it’s not possible to drive over there.