An instrument aboard one of the two NASA rovers en route to Mars has malfunctioned, prompting worries it could harm the robot’s information-gathering ability, a scientist said Wednesday. If left unfixed, the instrument could still determine the presence of iron-bearing minerals in the rocks and soil on the Martian surface, but not their relative abundance, said Steve Squyres, of Cornell University. Some of that information could be derived from the rover’s other instruments, however. Scientists hope that testing the minerals will help solve the riddle of whether Mars was ever a warmer, wetter place capable of sustaining life.