Summary
Io in rotation, by Voyager 2
Original caption
During its 1979 flyby, Voyager 2 observed Io only from a distance. However, the volcanic activity discovered by Voyager 1 months earlier was readily visible. This sequence of nine color images was collected using the Blue, Green and Orange filters from about 1.2 million kilometers. A 2.5 hour period is covered during which Io rotates 7 degrees.
Rotating into view over the limb of Io are the plumes of the volcanoes Amirani (top) and Maui (lower). These plumes are very distinct against the black sky because they are being illuminated from behind. Notice that as Io rotates, the proportion of Io which is sunlit decreases greatly. This changing phase angle is because Io is moving between the spacecraft and the Sun.
This time-lapse movie was produced at JPL by the Image Processing Laboratory in 1985.
Copyright status
This image is credited to NASA and the Jet Propulsion Laboratory. Per JPL/NASA policy and applicable United States federal law, such images are in the public domain, or, if they are owned by individuals or institutions other than NASA or JPL, may be used for any journalistic, educational, or personal purpose (but not a commercial purpose) without further authorization. NASA and JPL images, other than their respective institutional logos, or photographs of actual persons, are not subject to copyright and may be used without additional permission, unless otherwise declared. For details, see the JPL Image Use Policy Declaration.
Source
NASA/JPL, <http://photojournal.jpl.nasa.gov/archive/PIA02857.gif>
