A European space telescope that is using a technique known as astrometry to provide a precise three-dimensional map of more than one billion stars in the Milky Way galaxy. It was launched December 19, 2013, from the Kourou launch center in French Guiana. It will measure the distances to stars and plot their motions across the sky, as well as providing basic information about the stars themselves. It also is expected to discover thousands of exoplanets, as well as comets and asteroids in the solar system.