Dawn traveled through space using a technology called ion propulsion, in which ions are accelerated out of an engine, giving the spacecraft thrust. The xenon ions glow with blue light.
Image credit: NASA/JPL-Caltech

On this date in 2007, NASA launched the unmanned probe Dawn. Using ion engines and a Mars flyby in February 2009, Dawn reached the asteroid Vesta in 2011 and, for the first time, flew to a second target: the dwarf planet Ceres, in 2015. You can read all about Dawn and its findings at NASA’s pages here.