The Cassini spacecraft flew by Dione, one of Saturn's icy moons, on 7 April 2010. During that flyby, instruments detected molecular oxygen ions around the moon. Tokar et al. used those measurements to estimate the density of the molecular oxygen ions to be in the range of 0.01 to 0.09 ions per cubic centimeter (or ions per 0.06 cubic inch). These molecular oxygen ions are produced when neutral molecules are ionized; the measurements confirm that a neutral exosphere surrounds Dione.