All the Cool Planets Are Found by Microlensing
David Bennett
NASA/University of Maryland

NASA’s Kepler mission has led a revolution in our understanding of extrasolar planetary systems, and TESS is just beginning to find a wealth of nearby exoplanets that can be studied in detail by JWST. However, these missions are not sensitive to cooler planets that form beyond the snow line, where planet formation is thought to be most efficient. In fact, analogs of the planets in our own Solar System are invisible to these missions. The Astro2010 decadal survey selected the WFIRST exoplanet microlensing survey to fill this gap in our understanding of the cool planets using ~25% of the total WFIRST observing time. WFIRST will complement the exoplanet statistics from Kepler with sensitivity to planets below an Earth masses at separations ranging from the habitable zone of FGK stars to infinity (i.e. unbound planets). This demographic data will be crucial for the understanding of the planet formation process, including the delivery of water to planets in the habitable zone. I present recent results from ground based microlensing observations that challenge a key aspect of the core accretion theory, and I also present results from Keck adaptive optics imaging that determine are used to determine the masses of the exoplanets and host stars found by microlensing. These data are a;sp being used to develop the exoplanet mass measurement method that will be used by WFIRST.