Department of Earth Sciences

PLATO (PLAnetary Transits and Oscillations of stars) is a space mission of the European SPACE agency ESA, supposed to start in 2026 and to search for exoplanets orbiting stars similar to our Sun, beginning in 2027. Its aim is to find planets similar to Earth, moving in the habitable zone – i.e. in a distance to its star in which moderate temperatures and hence liquid water could exist.

The Freie Universität Berlin is actively involved in the mission via several members of the Planetary Sciences and Remote Sensing Group. Several scientists of the subject area are part of the international PLATO Mission Consortium, consisting of individual persons and more than 100 universities and research centers. The consortium is headed by Prof. Dr. Heike Rauer, who has played a key role in shaping the mission since its inception.

The PLATO mission combines high-precision observations from space with additional measurements from telescopes on Earth.

Combining both kinds of measurements will allow to conclude important characteristics of the discovered planets, such as size, density and orbit, which provide crucial information about their possible composition and formation.

Instead of a single telescope with a large mirror, PLATO utilizes 26 separate optical cameras. 24 of those, the “normal cameras”, measure the stellar brightness and are read out every 25 seconds. They are divided into four groups, where six cameras each have the same viewing field. The groups’ viewing fields are offset from each other, so that the central part of the PLATO field is observed by all 24 cameras, while the outer areas are only measured by 18, 12 or 6 cameras. A depiction of PLATO’s viewing field can be found here: Nascimbeni et al. A&A, 694, A313 (2025). The whole field of the normal cameras has a size of 49°x49°, which corresponds to about 5% of the whole firmament. 

The other two cameras, called “fast cameras”, are read out every 2.5 seconds. They measure only the brightest stars in the viewing field and the satellite uses their data, to align itself precisely and maintain its viewing direction. Additionally, these two cameras have a red filter on one and a blue filter on the other, so that transits around the brightest stars can be recorded in two different wavelength regimes. The cameras, their optical bench, and the electronics for reading out and processing the measurement data form the so-called payload, one of the two major parts of the PLATO satellite. The other is the service module, which houses systems for the satellite’s steering and alignment, as well as the communication module. 

The PLATO space telescope finds planets using the transit method: if the planet passes in front of its star from our point of view, it blocks a little of the starlight, leading to a small but measurable dimming. PLATO measures the brightness of over 250,000 stars over a long period of time in order to detect these recurring dimmings and thus find planets. The size of the decrease provides us with the size of the planet. PLATO can also determine the mass, radius and age of the star by using astroseismology, which is invaluable for characterizing the planet in more detail.

In order to be independent of the influence of the Earth's atmosphere and the Earth's day-night rhythm, PLATO will work at the so-called Lagrange point L2, around 1.5 million kilometers away from the Earth. As part of the PLATO mission, follow-up observations will then be carried out with telescopes on Earth to determine the planetary mass of the planet candidates found in this way.

PLATO is a mission by the European Space Agency ESA, implemented in collaboration with the international PLATO Mission Consortium. The consortium provides part of the payload, the scientific data processing center, the scientific data processing pipeline, and it supports ESA in the instrument’s technical characterization and ensuring the required measurement accuracy by using PLATO camera test data.

The consortium is headed by Prof. Dr. Heike Rauer, who is working both at the Institute of Geological Sciences of Freie Universität Berlin and at the German Aerospace Center (DLR). Scientists from the Planetology and Remote Sensing specialty make important contributions to preparing the technical and scientific data analysis. Below, the Freie Universität employees working for PLATO describe their contributions to this huge mission in more detail.

The satellite’s construction and assembly is in the hands of several industrial partners under the direction of OHB System AG (Deutschland), in collaboration with Thales Alenia Space (France, Italy), and Beyond Gravity (Switzerland). PLATO is a prime example of a successful European major mission – carried by international cooperation between research and industry.

In July 2010, the European Space Agency ESA opened their third call for proposals for a medium (M) mission. From the mission proposals submitted, ESA selected four candidates for further studies in February 2011, including PLATO. In February 2014, ESA then selected PLATO as the M3 mission from these four candidates.

After further studies in which individual PLATO systems were defined in more detail, ESA included PLATO in its science program in 2017, marking the transition from the development phase to actual construction. A call for bids to construct individual parts of the satellite followed. In October 2018, ESA transferred the management of the construction to OHB System AG.

At the end of June 2024, the first of the 24 “normal cameras” was mounted on the payload module’s optical bench, and aligned very precisely; the last of them was mounted in May 2025. The two “fast cameras” were added a short time later. Further, in June 2025, the service module and the payload module were joined in an elaborate procedure known as “mating”.

PLATO is due to be launched at the end of 2026 on an Ariane 6 rocket and will be positioned behind the Earth (as seen from the Sun) at a distance of 1.5 million kilometers. Measurements are expected to begin in 2027.