NASA scientists said the Mars rover Opportunity began scanning a stadium-sized crater for clues to what the Red Planet was like before volcanic eruptions covered its surface in lava.
Opportunity has been perched on the rim of a 130-metre wide crater dubbed Endurance since early May. It has been using its remote sensing instruments to study the rocks exposed in the steep sides of the crater.
A dark layer of rock, one to two metres deep, particularly intrigued mission scientists because it looked so different to the lighter-coloured rocks that Opportunity had studied at its landing site, the smaller Eagle crater. The composition of the latter rocks indicated that water had once washed over them.
According to Philip Christensen, from Arizona State University in Tempe, the dark layer in Endurance is most likely to be a sandstone made of grains of basalt. This suggestion is based on data from a remote sensing instrument on Opportunity called Mini-TES, which uses infrared radiation to identify minerals, informs newscientist.com
According to BBC Lion Stone is peppered with spherical "concretions", exhibits fine layering and is rich in sulphur, Nasa says.
The concretions probably formed when minerals precipitated out of water.
These tiny spheres were found in the rock outcrops and soil in Eagle Crater, where Opportunity touched down. But the presence of sulphur in Lion Stone is a promising sign to mission scientists that the rocks Opportunity is now examining were deposited in water. On Earth, rocks with as much salt as these Mars rocks either have formed in water or, after formation, have been highly altered by long exposure to water. Opportunity is one of two robotic geologists that arrived on opposite sides of Mars in January to discover whether the arid planet once held enough water to support life.
Scientists at NASA's Jet Propulsion Laboratory in Pasadena, California, announced in March that Opportunity had found evidence that a salty sea once covered its landing on a flat plain known as the Meridiani Planum.
Its twin rover, Spirit, also found evidence that small amounts of water were involved in forming the rocks it examined in the Gusev Crater, a massive depression the size of Connecticut, which scientists believed was a dry lake bed.
JPL scientists hope Opportunity's latest observations at Endurance Crater will unlock an even earlier chapter in the planet's environmental history than the water-bearing rock it discovered in Eagle Crater in March, reports reuters.com