Astronomy Picture of the Day . Ganymede: A Really Groovy Moon . ... Credit: Galileo Mission Team , Galileo Spacecraft , NASA Explanation: Ganymede's surface is a wrinkled mess. As large ice-sheets shift on the moon's surface , parts of the surface buckle causing high ridges, deep furrows, and parallel grooves. ... The Galileo spacecraft has also just discovered that Ganymede has a region of orbiting charged particles called a magnetosphere - a first for any moon. ... NASA Official: Jay Norris. ...