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Saturn's Two-Faced Moon.
2004 Why does Iapetus have a dark side and bright side? That's a mystery scientists hope that the Cassini spacecraft will be able to solve as it spends the next few years orbiting the Saturnian system. The unusual light/dark nature of the Moon was first revealed when the Voyager spacecraft swept past the Moon more than 20 years ago. One theory is that the Moon was coated by some other foreign material, but only on one side. Another idea is that it's being resurfaced from material inside the moon. This image was taken when Cassini was 3 million kilometres (1.8 million miles) away.
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.
At 1436 kilometers (892 miles across), Iapetus is about 2.5 times smaller than our own Moon.
The brightness variations in this image are real. The face of Iapetus visible here was observed at a Sun-Iapetus-spacecraft, or phase, angle of about 10 degrees.
The image was taken in visible light with the narrow angle camera on July 3, 2004, from a distance of 3 million kilometers (1.8 million miles) from Iapetus. The image scale is 18 kilometers (11 miles) 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. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.
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