Saturn's Two-Face Moon
The moon with the split personality, Iapetus, presents a puzzling appearance. One hemisphere of the moon is very dark, while the other is very bright. Whether the moon is being coated by foreign material or being resurfaced by material from within is not yet known.
Iapetus' diameter is about one third that of our own moon at 1436 kilometres. The latest image was taken in visible light with the Cassini spacecraft narrow angle camera on 3 July 2004, from a distance of 3 million kilometres from Iapetus.
The brightness variations in this image are not due to shadowing, they are real. The face of Iapetus visible was observed at a Sun-Iapetus-spacecraft, or phase, angle of about 10 degrees. The image scale is 18 kilometres per pixel. The image was 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.