The Kepler mission will observe ~120,000 stars to detect 0.01% drops in
brightness due to transits of Earth-sized planets, which must be recognized
against intrinsic stellar variability, detector and photon noise. We examined
a backside-illuminated CCD under Kepler-like conditions, and obtained a total
precision of 1.3¥10-5 at a flux of 1010 e-, indicating a detector error
of 7¥10-6. Using ACRIM1 solar irradiation measurements as a baseline, we
conclude that intrinsic stellar variability, together with the expected photon
and detector noise, provide an average SNR of 8-sigma for four transit events,
yielding an 85% detection rate with less than one false alarm for the entire
mission.
