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Universe of the Hubble Space Telescope 2001 Calendar

Jupiter is the fifth planet from the Sun, named after the Roman supreme god and patron of the Roman state. Jupiter is the largest planet in the solar system, with a diameter of 138,000 km (86,000 mi), a mass 318 times the mass of Earth, an orbital period of 11.9 years, and an average distance of around 800 million km (500 million mi). Io is one of the four largest moons of Jupiter (together with Europa, Ganymede, and Callisto) discovered by the Italian astronomer Galileo Galilei (1564­­1642) in 1610. This image, which was obtained by the Hubble Space Telescope on July 22, 1997, shows Io passing over Jupiter's turbulent clouds. The bright patches on Io are regions of sulfur dioxide frost; the white and brown areas on Jupiter are regions of high-altitude haze.