The dark material that coats one hemisphere of Iapetus is very dark indeed, as these two processed views of the same image demonstrate.
The image at left has been cleaned of cosmic rays and magnified; in this otherwise unenhanced view, only a small part of the moon's surface, at the bottom, is visible because it is part of the 'bright side' of Iapetus. (Only the right hand side of Iapetus is illuminated by sunlight.) The same image, shown on the right, has been contrast enhanced to make visible the part of the illuminated side of Iapetus that is coated with dark material.
The image was taken in visible light, with the narrow angle camera on July 19, 2004, from a distance of 2.9 million kilometers (1.8 million miles) from Iapetus, and at a Sun-Iapetus-spacecraft, or phase, angle of 89 degrees. The image scale is 17 kilometers (11 miles) per pixel. The image has been magnified by a factor of two to aid visibility.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.