PLATO: PLAnetary Transits and Oscillations of stars
by Ruth Titz-Weider (DLR), August 2024, revised March 2025
Mission idea
To date, we have not found an Earth-like exoplanet in the life-friendly, habitable zone around a solar-like star, even though there were occasional sensational media reports in the last few decades. Earth-like in this case means that it resembles Earth. For example, that it has a similar radius and mass, that it is very likely a rocky planet, and and that its orbital period around its star – which is similar to our Sun – is about one year. That would mean that the planet is at a distance that its surface exhibits moderate temperatures. We may have found some planets with similar mass or radius, but often both values are not well known simultaneously, or we cannot clearly classify the star and its age.
Artist’s depiction of the PLATO-satellite. Credit: ©ESA / ATG medialab
The explicit goal of PLATO is: to find rocky planets in the habitable zone of solar-like stars and to characterize them further. The mission also includes an accurate study of the host stars, including determining its age.
Organisation
PLATO is a satellite mission of ESA, the European Space Agency, which was chosen in 2014 as a so-called M-class-mission (M3) as part of the “Cosmic Vision” program. The satellite and its payload are jointly developed by ESA and an international consortium of science institutes. Both are supported by numerous industrial suppliers. The nominal mission duration is four years, and the technical specifications allow service of 8.5 years in total.
Sticker of the PLATO Mission Consortiums with flags of participating countries. Credit: DLR under CC BY-NC-ND 3.0
Instrument
The PLATO payload features a novel telescope design with 26 cameras. Each camera is equipped with a wide-angle lens with an aperture of 12 cm and four large-format CCD sensors in the focal plane. The sensors are sensitive in visible light. 24 of these cameras, the so-called ‘normal’ cameras, will observe more than 100,000 stars to detect planetary transits. The other two cameras have a special task. They read out the CCD very frequently – every 2.5 seconds versus 25 seconds – to ensure the satellite’s exact orientation. These two ‘fast’ cameras are equipped with a special red or blue filter, so that transit events can be recorded in both wavelength bands.
Illustration of a PLATO camera: the optics are located in the tube, the protective shield at the top is intended to prevent stray light from entering the camera. Credit: PLATO Mission Consortium
Where are PLATO’s targets?
Six cameras each form a group whose fields of view are slightly offset from each other. The central field is covered by all 26 cameras, while the outer areas are covered by 18, 12 and six cameras. Stars in the central field are therefore measured with a higher photometric precision than those in the periphery. This large field, approximately 49° x 49°, corresponds to around 5% of the entire celestial sphere.
A depiction of PLATO’s field of view can be seen here: Nascimbeni et al. A&A, 694, A313 (2025)
The selection of the target fields is based on a long and in-depth optimization process. In 2023, the first target field was selected. PLATO will observe it for a long time, more than a year. The selection of the fields is crucial for the mission in order to get the right stars in view. This target field is located near the star Canopus in the constellation Carina. A possible second
An image of the PLATO target field can be seen here: Nascimbeni et al. A&A, 694, A313 (2025). The image shows PLATO’s first target field (blue, lower left), a possible second field to be observed later in the mission’s lifetime (blue, upper right), as well as for comparision the fields of the Kepler/K2 mission (magenta/green respectively) and CoRoT (red).
Ground-based telescopes, will determine the mass of PLATO detected planets using the radial velocity method.
Orbit
Like the James Webb Space Telescope, PLATO will work at the so-called Lagrange point 2. This point, or rather area, is about 1.5 million kilometers away from Earth in the extension of the line connecting the Sun and Earth. Here, the space probe can “rest” without using any energy.
Schematic “top down” view of the Earth’s orbit around the Sun, with the 5 stable Lagrange points L1 to L5 shown. PLATO will orbit around L2 (on the right). Credit: NASA, STScI
Expectations
PLATO will observe bright stars. The most interesting ones form a group of about 15,000 dwarf stars and subgiants whose spectral type lies between F5 and K7 with magnitudes of less than 11 magnitudes. For these objects, the planetary and stellar parameters will be determined with the highest accuracy.
A second group is primarily used for statistical purposes. The light curves are already calculated on board to reduce the amount of data. This group comprises around 250,000 stars, including dwarf stars and subgiants, but also includes fainter stars with a brightness of less than 13 magnitudes. For most of these stars there will be a good radius determination, but not necessarily astroseismology or follow-up measurements by the radial velocity method.
It is exciting to wait for PLATO’s launch end of 2026 with an Ariane-6 launcher, and for the first measurements to come in.
To learn more about the mission, visit the PLATO mission site at ESA or the PLATO mission consortium website.
You can read about the PLATO mission in scientific detail in the recent review paper: Rauer et al. (2024)