This mosaic includes images taken by NASA's Galileo spacecraft during nine orbits around Jupiter and its four largest satellites. From left to right, the moons shown are Io, Europa, Ganymede, and Callisto. Galileo's solid state imaging camera built surface views in different colors and at varying resolutions. Most of the images were acquired between June 1996 and June 1997 by Galileo, but three images- Callisto in the top row, Ganymede in the middle row and Io in the bottom row-are from Voyager's mission to Jupiter in 1979.
The top row displays the relative sizes of the moons in global views at relatively low resolution. The images, scaled to about 10 kilometers (3.9 miles) per picture element (pixel), feature the smallest visible features of about 20 kilometers (12.4 miles). Surfaces are affected by tectonic or volcanic changes in the moons' interiors or by exterior deposition. Middle row images show regional views of up to 10 times higher resolution, each covering an area about 1,000 by 750 kilometers (621 by 466 miles) and scaled to about 1.8 kilometer (1.1 mile) per pixel. Regional features include volcanic cauldera fields on Io, tidally-induced cracks thousands of kilometers long on Europa, bright grooved regions on Ganymede, and enormous impact basins on Callisto caused by impacts with primitive comets or asteroids. Bottom row views represent the highest resolutions, covering areas about 100 by 75 kilometers (62 by 47 miles) and scaled to about 180 meters (197 yards) per pixel. The images show Io's volcanic plume vents, Europa's abundant ridges, Ganymede's fractured, grooved terrain, and Callisto's heavily eroded and mantled craters.
Spectral regions not visible to the eye are shown, indicating differences in surface chemical composition or changes in the way the surface reflects sunlight. For example, in the left middle image, bright red depicts newly-ejected volcanic material on Io, and the surrounding yellow materials are older sulphur deposits. The picture to its right shows enormous cracks in Europa's icy shell. Blue represents ice and reddish areas probably represent a thin coating of darker material ejected by ice volcanoes along the cracks.
The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov.