Jupiter is the largest planet and is fifth from the sun. It is the third-brightest spot in our skies — after the sun and Venus. Jupiter is made up almost entirely of gas, which means it doesn't have a solid surface like Earth does. Because of its vast size, Jupiter is named after the Roman king of the gods. Jupiter is more massive than all the other planets put together twice.
This huge planet has 63 moons (at last count), the most of any of the planets. The four largest moons are Io, Europa, Ganymede, and Callisto. These four moons are among the very first things Galileo saw with his small telescope (in 1610). For its size, Jupiter spins amazingly fast, rotating once every 9.8 hours. It takes Jupiter 11.86 Earth years to orbit the sun. Scientists believe that life as we know it could not exist there. The temperature is very cold, and the surface of this gigantic planet is an ocean of liquid hydrogen that could be as much as 10,000 miles deep. If Jupiter were hollow, more than 1,300 Earths could fit inside it.
Looking at Jupiter even through a small telescope, it is easy to see that the surface is divided into distinct light and dark color bands. Not only are the bands different colors, but some move faster than others, and they move in opposite directions. This makes the outer layer of this gas planet a very turbulent place. Swirls of color make their way around the planet like thunderstorms here on Earth. The most famous of the "storms" is the Great Red Spot. This storm is large enough to hold more than two Earths, and it has been visible from Earth for more than 300 years. The Great Red Spot is actually a very large, very violent storm.
Spacecrafts Voyager 1 and 2 visited Jupiter on their amazing journeys through the solar system in 1979. One significant discovery they made is that Jupiter (like Saturn) has rings, although Jupiter's are very faint. The rings are dark and seem to be made of small bits of rocky material — rocky material that comes and goes very quickly. In 1995, the spacecraft Galileo spent eight years orbiting Jupiter, and the Hubble Space Telescope still sends back information about the planet.
The giant planet's gravity attracts stray objects that wander into our solar system from time to time. The most famous of these objects, Comet Shoemaker-Levy 9, crashed into Jupiter during the summer of 1994. It left dark sports in the planet's atmosphere that were visible for many months afterward. By the time Comet Shoemaker-Levy 9 got close to Jupiter, it had broken into several pieces, receiving the nickname "a string of pearls."
