Jupiter is the largest planet in our solar system with a diameter of 143,000 km (88,700 miles). For comparison, Earth's diameter is 12,800 km. Jupiter also has 318 times the mass of Earth and almost 2.5 times the surface gravity that Earth has.
Jupiter rotates very quickly on its axis. The planet makes one complete rotation in 9 hours, 55 minutes, and 30 seconds (Maran, 2005).
Jupiter is the fifth furthest planet from the Sun in our solar system. It is 778.3 million km (484 million miles) away from the Sun. By comparison, Earth is only 149.6 million km from the Sun. It takes Jupiter 4,333 Earth days to make one complete orbit around the sun (Gierasch and Nicholson, 2004), compared to Earth's 365 day orbit.
Jupiter has 61 moons in orbit around it (Chaisson and McMillan, 2005). The top photo, taken by Voyager 1, shows Jupiter and its four largest moons. These four moons from largest to smallest are Ganymede, Callisto, Io, and Europa. Jupiters four large moons are often of more interest to scientists than planet Jupiter itself. All four of these moons were discovered by Galileo in 1610.
Jupiter's Composition and Atmosphere
Scientists believe that Jupiter is composed mainly of hydrogen and helium, with trace amounts of water vapor, ammonia, methane, and a few other gases. Sulfur and phosphorus are also thought to be present.
Unlike Earth, Jupiter is not a terrestrial planet. Instead Jupiter is mostly composed of gas and liquid and doesn't really have a solid surface.
When we view Jupiter what we are seeing is Jupiter's clouds. These clouds have regions of darker and lighter areas. Scientists refer to the darker regions as belts and the lighter regions as zones.
Jupiter's clouds are composed of three layers. The clouds in the outermost layer are composed of ammonia ice, the middle layer is composed of ammonium hydrosulfide, and the innermost layer is composed of water vapor (Chaisson and McMillan, 2005). Lightning is often associated with Jupiter's clouds.
Jupiter's Red Spot
The photo showing Jupiter's giant red spot was taken by Voyager 2. Scientists believe that the red spot is a massive hurricane-strength storm on Jupiter that has lasted for over 300 hundred years. The gases in the red spot swirl counterclockwise in the storm, except for in the very center, where everything is very still.
All of the gas planets in our solar system have rings like Saturn does, but the rings of Jupiter are not as spectacular as Saturn's. Jupiter's rings consists of small gravel-sized rocks to large boulders. The rings are surrounded by smaller dust particles.
Scientists haven't been able to view the surface or interior of Jupiter at this time. However, scientists believe that Jupiter may have a rocky core that is surrounded by a layer of liquid metallic hydrogen. This metallic layer of hydrogen is surrounded by a layer of nonmetallic or molecular hydrogen, which is surrounded by the gaseous clouds.
Jupiter also has a very strong magnetic field.
Chaisson, E. and McMillan, S. (2005). Astronomy Today. Pearson Prentice Hall: Upper Saddle River, NJ.
Gierasch, Peter J., and Philip D. Nicholson. "Jupiter." World Book Online Reference Center. 2004. World Book, Inc. (http://www.worldbookonline.com/wb/Article?id=ar293080.)
Maran, S. P. (2005). Astronomy for Dummies. Wiley: Indianapolis, IN.
Images of Jupiter: Courtesy of NASA/JPL-Caltech.