NASA scientists are excitedly speculating that discoveries made by a Mars rover over the weekend will help them finally unravel whether water played a role in the Red Planet’s geologic history, a science team member said on Monday. Scientists were poring over data and microscopic images returned to Earth by the rover Opportunity, which spent the weekend examining a multilayered rock nicknamed El Capitan embedded in the side of the small crater where Opportunity landed on Jan. 24.