This picture of Io is a combination of high resolution black and white images taken by NASA's Galileo spacecraft on 10 October 1999 and lower resolution color images taken by Galileo on 3 July 1999. The color mosaic was created from images taken using the camera's near-infrared, green, and violet filters (slightly more than the visible range) and has been processed to enhance more subtle color variations (see true color and false color global mosaics for comparison). The color mosaic illustrates the wide variety of materials on Io's surface, however, the illumination of the color images is poor for showing topographic shading. The higher resolution images were taken just before local sunset so long shadows enhance the topography and surface texture.
The combination allows scientists to better understand the relationships between the different surface materials and the underlying geologic structures. For example there is red material, which is often associated with areas where lava is erupting onto the surface and is thought to be a compound of sulfur, around the margin of Monan Patera (the elongated caldera just to the lower right of center). The broad circle of bright, white material (just to the left of center) is thought to be sulfur-dioxide which is being deposited from the plume Amirani.
The lengths of the shadows cast by the mountains make it possible to estimate the mountains' heights. The southern mountain on the far right of the mosaic is approximately 8 kilometers (26,000 feet) high and the mountain to the north of it is approximately 4 kilometers (13,000 feet) high.
The image is centered at 22.8 degrees north latitude and 109.5 degrees west longitude and north is to the top. The higher resolution images have a resolution of ~500 meters (or yards) per picture element and they are illuminated from the left. These images were taken on October 10, 1999 at a range of 25,000 kilometers (15,500 miles). The color images are illuminated from almost directly behind the spacecraft. The resolution of the color images is 1.3 kilometers (0.8 miles) per picture element. They were taken on July 3, 1999 at a distance of about 130,000 kilometers (81,000 miles) by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft.
Image produced by: Moses Milazzo, Planetary Image Research Lab. (PIRL), Lunar and Planetary Lab. (LPL), University of Arizona
The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is a division of the California Institute of Technology, Pasadena, CA.
This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at http://galileo.jpl.nasa.gov/. Background information and educational context for the images can be found at http://galileo.jpl.nasa.gov/images/io/ioimages.html.
NASA's Planetary Photojournal PIA-02526
March 6, 2000