This artist's impression shows exoplanet HD 189733B as it passes in front of its parent star, called HD 189733A. Hubble Space Telescope's instruments observed the system in 2010, and in 2011, following a large flare from the star (depicted in the image). In this picture, the surface of the star, which is around 80% the mass of the Sun, is based on observations of the Sun from the Solar Dynamics Observatory. While around a thousand such exoplanets (planets that exist in the Milky Way outside our Solar System) have been discovered, billions more are expected to exist.