Io is the most volcanically active body in the solar system, with volcanoes that erupt massive volumes of silicate lava, sulphur and sulphur dioxide, constantly changing Io’s appearance. This new basemap of Jupiter’s moon Io was produced by combining the best images of the Voyager 1 and Galileo missions.
This mosaic is made up of images taken at various local times of day, care was taken to note the solar illumination direction when deciding whether topographic features display positive or negative relief. In general, the illumination is from the west over longitudes 40 to 270 W, and from the east over longitudes 270 W to 40 W. Color information was later superimposed from Galileo low phase angle violet, green and near-infrared (756 nanometer wavelength) images. The Galileo SSI camera’s silicon CCD was sensitive to longer wavelengths than the vidicon cameras of Voyager, so that distinctions between red and yellow hues can be more easily discerned. The “true” colors that would be visible to the eye are similar but much more muted than shown here. Image resolutions range from 1 to 10 km/pixel along the equator, with the poorest coverage centered on longitude 50 W.
This mosaic is in an equal area cylindrical map projection, centered on longitude 180, with grid lines at 30 degree intervals. Full scale versions of this mosaic, and the data products used to generate it are available from the USGS Astrogeology website: http://astrogeology.usgs.gov/Projects/JupiterSatellites/.
For images of Io’s South Pole, visit http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=4903.Image credit: NASA/USGS/Tammy Becker and Paul Geissler