Galilean Moons of Jupiter
National Aeronautics and Space Administration 0 300,000,000 900,000,000 1,500,000,000 2,100,000,000 2,700,000,000 3,300,000,000 3,900,000,000 4,500,000,000 5,100,000,000 5,700,000,000 kilometers Galilean Moons of Jupiter www.nasa.gov The planet Jupiter’s four largest moons, or satellites, are called the same face towards Jupiter as they orbit, meaning that each SIGNIFICANT DATES the Galilean moons, after Italian astronomer Galileo Galilei, who moon turns once on its axis for every orbit around Jupiter. 1610 — Galileo Galilei and Simon Marius independently discover observed them in 1610. The German astronomer Simon Marius Voyagers 1 and 2 offered striking color views and global per- four moons orbiting Jupiter. This discovery, among others by apparently discovered them around the same time. The names spectives from their flybys of the Jupiter system in 1979. From Galileo, helped change the way people thought about the heav- Marius proposed for the moons in 1614 (suggested to him by a 1995 to 2003, the Galileo spacecraft made observations from ens. The prevailing idea of the time was that all heavenly bodies fellow astronomer, Johannes Kepler) are the ones we use today repeated elliptical orbits around Jupiter, making numerous close orbit the Earth: a planet with its own small orbiting bodies did — Io, Europa, Ganymede, and Callisto. approaches over the surfaces of the Galilean moons and pro- not conform to this geocentric model. Io is the most volcanically active body in the solar system. Its ducing images with unprecedented detail of selected portions of 1979 — Voyager 1 photographs an erupting volcano on Io: the surface is covered by sulfur and lava in many colorful forms.
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