Opportunity (and its late twin, Spirit) have found plenty of evidence for a watery Martian past. But this fall, Opportunity spotted something unusual
that had scientists buzzing. These strange spherules could be the work of water, they could be left over from a major crater-causing impact, or something else scientists still don't understand.
They are made of basalt and apparently crunchy on the outside but soft on the inside. If they are evidence of sedimentary deposits, that's an indication that water once moved through the rocky outcrops where Opportunity has been exploring, along the rim of a crater called Endeavour. Mars Exploration Rover mission scientists said it was one of the most exciting finds in the nearly nine-year-old mission.