Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2007 September 19
See Explanation.  Clicking on the picture will download
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4,000 Kilometers Above Saturn's Iapetus
Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

Explanation: What does the surface of Saturn's mysterious moon Iapetus look like? To help find out, the robotic Cassini spacecraft now orbiting Saturn was sent soaring last week just 2,000 kilometers from the unique equatorial ridge of the unusual walnut-shaped two-toned moon. The above image from Cassini is from about 4,000 kilometers out and allows objects under 100-meters across to be resolved. Cassini found an ancient and battered landscape of craters, sloping hills, and mountains as high as 10 kilometers and so rival the 8.8-kilometer height of Mt. Everest on Earth. Just above the center of this image is a small bright patch where an impacting rock might have uncovered deep clean water ice. Space scientists will be studying flyby images like this for clues to the origin of Iapetus' unusual shape and coloring with particular emphasis because no more close flybys of the enigmatic world are planned.

APOD editor to review best space pictures in Philadelphia next Wednesday
Tomorrow's picture: Northern Cygnus

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