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four galilean satellites

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Range : 7 million kilometers (4.3 million miles) Io is Jupiter's innermost of the four Galilean satellites. Photo taken at 2:00 AM through an ultraviolet filter. The photo's background is part of Jupiter's disk. North is at the top and the central longitude of Io is 180 degrees. Io shows a contrasting surface with dark polar areas and many light and dark regions around the equator. This resolution of about 100 miles/160 kilometers, no topographic features, like craters, can be seen. The brighter regions may be areas containing sulfur and various salts, making Io very reflective(six times brighter thanb Earth's Moon). Io is about the same size and density as our Moon, but has followed a different evolutionary path, influenced by its closeness to Jupiter and the intense bombardment it receives from the Jovian radiation belts of energetic charged particles. ARC-1979-A79-7022

Range : 7 million kilometers (4.3 million miles) Io is Jupiter's inner...

Range : 7 million kilometers (4.3 million miles) Io is Jupiter's innermost of the four Galilean satellites. Photo taken at 2:00 AM through an ultraviolet filter. The photo's background is part of Jupiter's dis... More

This photo of Callisto, outermost of Jupiter's four Galilean satellites, was taken a few minutes after midnight (PST) Feb. 25 by Voyager 1. The distance to Callisto was 8,023,000 kilometers (4.98 million miles). The hemisphere in this picture shows a fairly uniform surface dotted with brighter spots that are up to several hundred kilometers across. Scientists believe the spots may be impact craters but higher-resolution photos will be necessary before the features can be interpreted. Callisto is about the same size as the planet Mercury--about 5,000 kilometers (3,000 miles) in diameter. Callisto is less massive than Mercury, however, giving it a density less than twice that of water. Scientists believe Callisto, therefore, is composed of a mixture of rock and ice (up to about 50 percent by weight). Its surface is darker than those of the other Galilean satellites, but is still about twice as bright as Earth's Moon. This black-and-white photo was taken through a violet filter. Jet Propulsion Laboratory manages and controls the Voyager project for NASA's Office of Space Science. (JPL ref. No. P-21149) ARC-1979-A79-7027

This photo of Callisto, outermost of Jupiter's four Galilean satellite...

This photo of Callisto, outermost of Jupiter's four Galilean satellites, was taken a few minutes after midnight (PST) Feb. 25 by Voyager 1. The distance to Callisto was 8,023,000 kilometers (4.98 million miles... More

Range : 241,000km (150,600 mi.). This black and white image of Europa, smallest of Jupiter's four Galilean satellites, was acquired by Voyager 2. Europa, the brightest of the Galiliean satellites, has a density slightly less than Io, suggesting it has a substantial quantity of water. Scientists previously speculated that the water must have cooled from the interior and formed a mantle of ice perhaps 100 km thick. The complex patterns on its surface suggest that the icy surface was fractured, and that the cracks filled with dark material from below. Very few impact craters are visible on the surface, suggesting that active processes on the surface are still modifying Europa. The tectonic pattern seen on its surface differs drastically from the fault systems seen on Ganymede where pieces of the crust have moved relative to each other. On Europa, the crust evidently fractures but the pieces remain in roughly their original position. ARC-1979-A79-7092

Range : 241,000km (150,600 mi.). This black and white image of Europa...

Range : 241,000km (150,600 mi.). This black and white image of Europa, smallest of Jupiter's four Galilean satellites, was acquired by Voyager 2. Europa, the brightest of the Galiliean satellites, has a densi... More

Galilean Satellites, Voyager Program, NASA/JPL Photo

Galilean Satellites, Voyager Program, NASA/JPL Photo

These photos of the four Galilean satellites of Jupiter were taken by NASA Voyager 1 during its approach to the planet in early March 1979. Io, Europa, Ganymede, and Callisto are shown in their correct relative... More