In 2027, ESA will launch PLATO — a space telescope with an ambitious goal: to find Earth-sized planets in the habitable zones of nearby, Sun-like stars. But before the planet hunt begins, a fundamental question must be answered: which stars to watch?
A new paper from the mission consortium describes the selection of the Prime Sample — a curated set of 15,000 high-priority targets within PLATO's first southern observation field, LOPS2. These stars will receive dedicated ground-based follow-up: photometric confirmation of transit candidates and planet mass measurements via radial velocity curves.
Selection criteria include stellar brightness, spectral type, noise characteristics, and observational accessibility from Earth. The ranking methodology is general enough to be applied to any catalog of stars surveyed for transiting planets. The Prime Sample list will be made public nine months before launch, alongside ESA's first Guest Observer call for proposals.
PLATO will monitor the LOPS2 field continuously for at least two years — long enough to detect transits of planets with Earth-like orbital periods. If the mission succeeds, it would mark the first direct measurement of both the size and mass of a potentially Earth-like planet around a Sun-like star.