After reaching a deeper understanding of the subsurface ocean of Enceladus just yesterday, a stunning discovery has just been made about the largest Moon in the solar system.  The largest moon of Jupiter, Ganymede, contains a subsurface ocean of it’s own.  The discovery was made with the Hubble space telescope and a careful study of aurora on the giant moon. That’s right Ganymede has auroral activity.  This is because it is the only moon in the solar system with a magnetic field.  The magnetic field funnels radiation from the Sun toward the north and south poles, where it ionizes molecules...