The PLATO mission consortium finalized its star selection: 290,000 targets in total and the hunt for an “Earth twin” can commence.

The Scientific Consortium of the European space mission PLATO (PLAnetary Transits and Oscillations of stars) has made the PLATO Input Catalog (PIC) available to ESA: the definitive list of stars chosen as potential targets for observation over the coming years.

While the satellite’s pointing direction was established already in 2023, the list of target stars has now been determined. These stars are bright, isolated, and ideally positioned, giving PLATO the best chance of discovering and studying new exoplanets -- that is, planets orbiting other stars than our Sun. Some of these worlds could even be resembling Earth.

Starting in 2027, the satellite will monitor most of the 290,000 stars in the PIC, measuring the brightness every 25 to 600 seconds for the next years with its 26 telescopes. Its gaze will focus on a patch of the southern sky called the Long-Pointing Field South 2 (LOPS2), spanning 2,200 square degrees – roughly the same size as the sky we can see with the naked eye at any moment.

The goal is rather ambitious: to identify rocky planets in the so-called “habitable zone”, a promising region around a star where conditions might allow liquid water to exist – a key ingredient in enabling life as we know it! PLATO plans to tackle this challenge by focusing on Sun-like stars.

To achieve this feat, the spacecraft will search for tiny dips in the starlight caused by the planet passing by its host, known as a “transit”. Detecting an Earth-like planet around a Sun-like star produces a fluctuation of 0.0084%, comparable to a mosquito flying past a car’s headlight viewed several kilometers away.

Creating the PIC was far from straightforward. Beginning with a database of roughly 2 billion stars, most of them observed by Gaia (another ESA satellite), the team of Italian and other European researchers first narrowed the sample to 2.5 million dwarfs and sub-giants with surface temperatures between 3,500 and 7,000 °C (for comparison, the Sun’s surface temperature is around 6,000 °C) within the LOPS2 field.

From this pool, the selection became even more stringent. To identify the stars most promising for hosting a planet, Prof. Dr. Heike Rauer, the mission’s principal investigator at the Freie Universität Berlin and DLR, explains: “We focus primarily on stars that resemble the Sun. For planets orbiting such stars, we can best assess whether any of them might harbor liquid water on their surfaces. However, we also include cooler and hotter stars in order to better understand these other types of planetary systems.”

After applying these criteria, the original two billion stars were ultimately distilled down to the 290,000 targets that now form the catalog.

PLATO operates as a strong team player alongside its space-based counterparts. Many of the tens of thousands of stars observed by the ongoing TESS mission fall within PLATO’s LOPS2 field, creating valuable opportunities to confirm planet candidates and extend observational baselines. Some of PLATO’s new discoveries can also be tracked with the smaller ESA mission CHEOPS, further enhancing the planetary signal through combined data. Exoplanets that possess an atmosphere can also be characterized in greater detail by James Webb Space Telescope or by the upcoming Ariel, scheduled for launch in 2029.

Regardless, estimates indicate that in its 4.5 years of activity, PLATO will discover thousands of new exoplanets, of which about hundreds will be rocky planets. It will be particularly exciting to see how many of them turn out to orbit within the habitable zone of their host stars.

Beyond its exoplanet targets, the PIC also includes stars used to maintain the satellite’s long-term pointing stability, calibrate onboard instruments, and refine models that determine stellar mass, radius, and age. Known planet hosts and planet candidates are certainly included as well.

The PLATO mission’s international scientific consortium is led by Prof. Dr. Heike Rauer, planetary scientist at the Institute of Geological Sciences at the Freie Universität Berlin and the German Aerospace Center (DLR). Contributions to the mission are supported by scientists from the Freie Universität Berlin.

Contact

Prof. Dr. Heike Rauer, Planetary Science and Remote Sensing Group, Institute of Geological Sciences, Department of Earth Sciences, Freie Universität Berlin, and German Aerospace Center (DLR), Email: heike.rauer@fu-berlin.de

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The contributions by Freie Universität Berlin to the PLATO mission are supported by German Federal Government via the German Space Agency at DLR (Grants 50OO1401, 50OP2103 and 50OP2104).