Labels:text | electronics | screenshot | font | number | software OCR: Penguin Dictionary of Astronomy Contents Index Back History Io One of the four Galilean moons of Jupiter (number I), the nearest to the planet and arguably the most remarkable. Its surface is brightly coloured, in shades of red, orange and white. Eight active eruptive centres were identified in the images returned during the encounter of the . Voyager 1 spacecraft, six of which were still active when . Voyager 2 flew by four months later. The eruptive centres appear as dark spots. Many are surrounded by roughly circular 'halos', presumably of ejected material, and lava flows are also visible. The coloured crust is made of sulphur and solid sulphur dioxide. No impact craters are seen; any that were formed in Io's early history have long since been covered by erupted material. Io is the only ...
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