Seven planets of terrestrial size and moderate temperature gravitate around the star Trappist-1. Better: at least three of them are in conditions compatible with the presence of liquid water on the surface. This was discovered by an international team involving CNRS, CEA and UPMC researchers at the Bordeaux Astrophysics Laboratory (CNRS/Bordeaux University), the Dynamic Meteorology Laboratory (CNRS/UPMC/Polytechnic School/ENS) and the Astrophysics, Instrumentation and Modelling Laboratory (CNRS/CEA/Paris Diderot University). The planetary system orbiting the Trappist-1 star is one of the most surprising and richest to date, particularly in terms of scientific perspectives: beyond determining the orbit and mass of these planets, it will be possible, in the near future, to highlight the possible presence of atmospheres. This study is published in Nature on February 23, 2017.