PLATO was proposed in 2007 to European Space Agency (ESA) by a team of scientists in response to the call for ESA Cosmic Vision 2015–2025. The assessment phase was completed during 2009, and in May 2010 it entered the Definition Phase. Following a call for missions in July 2010, ESA selected in February 2011 four candidates for a medium-class mission (M3 mission) for a launch opportunity in 2024. PLATO was announced on 19 February 2014 as the selected M3 class science mission for implementation as part of its Cosmic Vision Programme. Other competing concepts that were studied included the four candidate missions EChO, LOFT, MarcoPolo-R and STE-QUEST.
PLATO is an acronym, but also the name of a philosopher in Classical Greece; Plato (428–348 BC) was looking for a physical law accounting for the orbit of planets (errant stars) and be able to satisfy the philosopher's needs for "uniformity" and "regularity".
The goal is to find planets like Earth, not just in terms of their size but in their potential for habitability. By using 34 separate small telescopes and cameras, PLATO will search for planets around up to one million stars. The main objective of PLATO is to elucidate the conditions for planet formation and the emergence of life. To achieve this objective, the mission has these goals:
Discover and characterise a large number of close-by exoplanetary systems, with a precision in the determination of the planet mass up to 10%, of planet radius of up to 2%, and of stellar age up to 10%.
Detect Earth-sized planets in the habitable zone around solar-type stars
Detect super-Earths in the habitable zone around solar-type stars
Measure solar oscillations in the host stars of exoplanets
The PLATO payload is based on a multi-telescope approach, involving a set of 32 "normal cameras" working at a readout cadence of 25 sec and monitoring stars fainter than mV = 8 (apparent visual magnitude), plus two "fast cameras" working at a cadence of 2.5 sec, and observing stars in the magnitude range 4 to 8. The cameras are based on a fully dioptric telescope including 6 lenses; each camera has an 1100 deg2 field, and a pupil diameter of 120 mm. Each camera is equipped with its own CCDfocal plane array, consisting of 4 CCDs with 4510 x 4510 pixels.
The 32 'normal cameras' are arranged in four groups of 8 cameras with their lines of sight offset by a 9.2° angle from the +ZPLM axis. This particular configuration allows surveying a total field of about 2250 deg2 per pointing. The satellite will be rotated around the mean line of sight by 90° every 3 months, for a continuous survey of exactly the same region of the sky.
PLATO will differ from COROT and Kepler space telescopes in that it will study relatively bright stars (between magnitudes 4 and 8) making it easier to confirm extrasolar planets using follow-up radial velocity measurements. It will have a much larger field of view than the Kepler mission (which has 100 deg2) allowing PLATO to study a larger sample of stars.
^PLATO: detailed design of the telescope optical units. Authors: D. Magrin, Ma. Munari, I. Pagano, D. Piazza, R. Ragazzoni, et al., in Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave, Edited by Oschmann, Jacobus M., Jr.; Clampin, Mark C.; MacEwen, Howard A. Proceedings of the SPIE, Volume 7731, pp. 773124-8 (2010)