Research on extrasolar planets addresses fundamental questions regarding planet formation, evolution and planetary habitability. Despite rapid progress over the past decades, our understanding of rocky planets orbiting within the habitable zones of their host stars — worlds that may potentially support life — remains limited. Only a small number of such planets are currently known, and their detection is strongly affected by observational biases. Moreover, many of the key properties required to assess planetary habitability, including bulk density, interior structure, and atmospheric composition, are still poorly constrained.

Transiting exoplanets — planets that pass in front of their host stars as seen from Earth — are especially valuable in this context. Transit observations enable detailed planetary characterization when combined with complementary techniques such as radial-velocity measurements and atmospheric spectroscopy. In addition, asteroseismology of the host stars can provide precise stellar ages, another fundamental parameter of a planetary system.

This talk presents an overview of the main methods used to detect and characterize exoplanets, with a particular focus on the transit technique. We will review the current   knowledge on small and potentially habitable exoplanets. In light of ESA’s upcoming PLATO mission, which aims on the detection and characterization of planets up to the habitable zone of solar-like stars, we discuss our expectations for planets in the habitable zone from this mission.