NASA's Mars 2020 Perseverance rover has begun its search for signs of ancient life on the Red Planet. Flexing its 7-foot (2-meter) mechanical arm, the rover is testing the sensitive detectors it carries, capturing their first science readings. Along with analyzing rocks using X-rays and ultraviolet light, the six-wheeled scientist will zoom in for closeups of tiny segments of rock surfaces that might show evidence of past microbial activity.