Jupiter is so vast that it exerts an enormous gravitational pull on things around it. This makes Jupiter like a gigantic vacuum cleaner. Asteroids and meteoroids that come near it are sucked up into its atmosphere. Jupiter is the largest planet. It weighs three hundred times more than Earth, and is more than twice as heavy as all the other planets added together! Over 1,400 earths could fit inside it. The core of Jupiter is rock and metal, possibly the size of the planet Earth. If it were possible to drive around Jupiter's equator in a car, the trip would take six months of nonstop 24 hour a day travel! A similar trip around the earth's equator would only take two weeks.
Jupiter is the fastest spinning of the planets. The fast rotation stirs the atmosphere and clouds into dark and light colored stripes called belts and zones. In 1995, the space probe Galileo sent a mini probe down into the atmosphere and found that the winds on Jupiter blew far stronger than any winds on Earth. Jupiter's Great Red Spot extends more than three times the Earth's diameter. The Great Red Spot lies across Jupiter's southern end. The spot is a giant storm that has been raging for over one hundred years.
Galileo Galilei was the first scientist to see any of Jupiter's moons. Using a telescope, he spied Ganymede, Europa, Callisto and Io. Scientists have found a dozen more moons since Galileo discovered the first four. One of Jupiter's moons, Ganymede, is the solar system's largest moon. It has a diameter of 3,210 miles. It is larger than the planet Mercury. Ganymede's core takes up half its diameter. Another moon, Callisto, has the most cratered surface of any moon in the solar system. This moon is made up of water, ice, and rock which give it its dark color. Jupiter's moon, Io has about 80 volcanoes. NASA's spacecraft Galileo found numerous volcanoes shooting 50 miles above Io's surface. Billions of years ago, Earth probably had as much volcano activity as Io has now. By studying Io, scientists hope to learn more about how Earth was formed.