Jupiter: King of Planets
1610 AD
1610 1610

NAT

FIFTH PLANET, SOLAR SYSTEM
	Why is it you never hear of plans to send astronauts to land on Jupiter?
	Well, who would want to? Jupiter is a huge planet composed primarily of a madly swirling, electrically-charged atmosphere with a liquid hydrogen ocean perhaps 10,000 miles deep. Some scientists theorize that there is a tiny rocky core deep within Jupiter's center just inside a sea of liquid metal. It is certainly not a hospitable place for astronauts to visit. 
	Jupiter is about 400 million miles from Earth. If you were to shine a laser toward the Jovian system, it would take 58 minutes for the beam -- travelling at 186,000 miles per hour -- to reach Jupiter.
	Looking from Earth with the naked eye, Jupiter looks like a very bright star. It is the largest of all the planets. In fact, if you put all eight of the other known planets together, Jupiter would still be one-and-a-half times larger than their combined size. More than 1,300 Earth's could comfortably fit inside Jupiter.
	In 1610 Galileo turned his telescope toward Jupiter and was surprised to see four additional bright dots near Jupiter's equator. As he watched over several evenings, he noticed that the dots moved. The dots were moons orbiting Jupiter! It turns out that Jupiter has its very own "solar system" of orbiting mini-planets.
	Jupiter and its largest moons, Io, Europa, Callisto, and Ganymede, were visited by the Voyager 1 and 2 spacecraft. Io, slightly larger than our moon, is an extremely active body. It has volcanos that erupt with such force that liquid sulfur is thrown hundreds of miles into space. This sulfur gives Io a reddish color. The other three major moons are rocky, cratered, and covered with ice. Twelve additional moons have been discovered since Galileo first looked toward the planet.
	In 1664, Robert Hooke discovered on Jupiter the solar system's largest and longest-lived superhurricane. The Great Red Spot, now at least 300 years old, is a vast planetary storm system so large that two Earths could fit inside.
	Because hydrogen is a wonderful rocket fuel and so much of Jupiter is made of this gas, some designers think it will make a fine "gas station" for future space flights to the farther reaches of our solar system and beyond.