Microlensing exoplanets from ground and space based surveys: the Roman Space Telescope microlensing survey.

Microlensing, with about 200 planetary systems known to date, is a key technique for the search and the characterization of exoplanets. In particular, microlensing allows to access relevant parts of the physical parameter spaces which are currently difficult to probe by other methods. As a main point, microlensing is sensitive to planets in bound systems located far enough (of order of a few AU) from their host star, beyond the snow line (a key location in the framework of planet formation theories), and is sensitive to low mass planets, in principle down to below Earth mass analogs. Additionally, microlensing is sensitive to planets distant from the solar neighbourhood, all the way to the Galactic bulge and in principle also to extragalatic planets. Finally, microlensing is sensitive to unbound planetary systems ("free floating planets"). In this summary I will focus on current results from ground-based surveys, the space-based Spitzer microlensing programs, which lasted 6 years, and the forecoming exoplanet microlensing survey with the Nancy Grace Roman Space Telescope.