When the first of two Mars Exploration Rovers lands on the red planet tomorrow night, scientists will be ready to begin collecting new evidence to try and solve the riddle of whether life has ever existed on Mars. The first rover to land, named Spirit, is expected to descend to the Martian surface at about 11:30 p.m. Eastern time tomorrow and will be guided — as it has been throughout its flight — by an embedded operating system from Wind River Systems Inc. in Alameda, Calif. The operating system will manage the trajectory, descent, operations control, data collection and communications of the missions, according to Wind River.