The spacecraft monitored the brightness of stars over time, searching for the slight dimming that happens in regular intervals when planets transit their host star. In every field, CoRoT recorded the brightness of thousands stars in the V-magnitude range from 11 to 16 for the extrasolar planet study. In fact, stellar targets brighter than 11 saturated the exoplanets CCD detectors, yielding inaccurate data, whilst stars dimmer than 16 don't deliver enough photons to allow planetary detections. CoRoT was sensitive enough to detect rocky planets with a radius two times larger than Earth, orbiting stars brighter than 14; it is also expected to discover new gas giants in the whole magnitude range.