PLATO’s primary goal is to detect exoplanet systems around stars that are bright enough and relatively close to us. It will also gather asteroseismology data to characterize them precisely and determine their age.
With the degree of photometric precision PLATO is designed to achieve, the diameters of planets will be determined with a margin of error of approximately 3%. Likewise, the uncertainty on the age, mass and radius of stars along the entire Hertzsprung-Russell diagram will be approximately 10%.
The orbit about L2 is a large-amplitude Lissajous orbit ranging from 500,000 to 400,000 km. The L2 point was chosen for its stable temperature and radiation environment, as well as for its eclipse-free orbit possibilities and the unobstructed view it offers of a large part of the sky (the Sun, Earth and Moon are all located within a relatively small angle as seen from the satellite).
In this orbit, PLATO will rotate periodically around its pointing axis to maintain the correct orientation of its sunshield. Orbit control manoeuvres will be performed monthly.
The mission is planned to last four years, in a series of phases still under discussion within the scientific consortium. The first two observation phases over a period of two years will each focus on a portion of the sky where models indicate a large number of cold dwarf stars are likely to be present. During this long period of observations, PLATO will be able to detect a number of transits of planets with an orbital period similar to that of Earth’s. The photometric precision will be 3.4 10-5 and the maximum magnitude (brightness) 11.
One of these fields of the sky will be centred on longitude λ = 210° and latitude β = -60° from the ecliptic, and the second around λ = 306° and β = 67°, close to the galactic plane (see map below).
These long observation periods reduce the risk of false positives caused by natural variations in star brightness, background objects or artefacts generated by the satellite itself. The third and last part of the mission will be a “step-and-stare” phase, during which different parts of the sky will be monitored for several months. This last phase will last for at least one year.
Areas of the sky already observed by CoRot and Kepler and future PLATO targets. The lighter “step-and-stare” target areas are indicative, as their exact location is yet to be determined.
Each area will contain at least 20,000 stars with a magnitude less than 8. They will be bright enough to further characterize them with large ground observatories.