Observation concept - PLATO
The measurement principle of PLATO is to carry out high precision, long (months to years), uninterrupted photometric monitoring in the visible band of very large samples of bright (mV ≤ 11–13) stars. The resulting light curves will be used for the detection of planetary transits, from which the planetary radii will be determined, and for the asteroseismology analysis to derive accurate stellar parameters and ages. Since the PLATO targets are bright, the masses of the detected planets can be determined from radial velocity observations at ground-based observatories.
The current baseline observing plan for the 4-year nominal science operations consists of long-duration observations of two sky fields lasting two years each. An alternative scenario is for operations split into a long-duration pointing lasting three years and a one-year step-and-stare phase with several pointings. In view of the exceptionally fast development of exoplanet science, the final observing strategy will be investigated throughout the mission development and decided two years before launch. Depending on the selected strategy, the mission will be able to cover between 10 per cent and 50 per cent of the sky during the nominal observing time.
In order to continuously monitor the star fields, so as not to miss any planetary transit, as well as to increase the signal-to-noise ratio for those transits and for asteroseismology mode detections, the science duty cycle of the mission has been set to be above 93%. Furthermore, periodic gaps must be avoided as required by the need to keep disturbing peaks away from the frequencies of interest in the power spectrum of star oscillations.