PASADENA, Calif., Feb. 5 (UPI) -- NASA's robot rover Opportunity has found round mineral grains in the Martian soil, a possible sign of water, mission scientists said Thursday.
Photos taken by the rover's microscopic imager show coarse soil grains of different shapes, including a few round ones, but the scarcity of the round grains means other forces also could be responsible for their shape, scientists said.
Another possible explanation is meteorite collisions with the planet, which could have produced the rounded grains by melting the surface rock on impact.
"We saw a bunch of really fine-grained stuff that we couldn't tell much about and then we saw these coarser grains on top," said principal Mars Exploration Rover investigator Steve Squyres. "We began to notice that some of these grains looked awfully darn round."
Because the rounded grains are so scarce, the mission team suspects they were formed when large meteors melted Martian rocks, spraying the resulting molten material out as a fine jet which cools to form a glass-like material.
Scientists said another possibility is the round grains in the soil are ash particles from a volcanic eruption.
