* Astronomy

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RE: Iapetus

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Darkness sweeps over Iapetus as the Cassini spacecraft watches the shadow of Saturn's B ring engulf the dichotomous moon. The image at left shows the unshaded moon, while at right, Iapetus sits in the shadow of the densest of Saturn's rings.
North on Iapetus is up and rotated eight degrees to the left.

Credit: NASA/JPL

The images were taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 13, 2007 at a distance of approximately 2.3 million kilometres from Iapetus. Image scale is 14 kilometres per pixel.

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This image of Iapetus was taken by the Cassini spaceprobe on February 12, 2007, when it was approximately 2,436,761 kilometres away.

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Credit: NASA/JPL/Space Science Institute

The image was taken using the P120 and GRN filters.

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The Cassini spacecraft continues to image terrain on Iapetus that is progressively eastward of the terrain it has previously seen illuminated by sunlight.

Credit: NASA/JPL/Space Science Institute

The region seen here was imaged in reflected light from Saturn at excellent resolution in the close flyby on New Year's Eve 2004.
This view looks toward the equator of Iapetus on the moon's Saturn-facing side. North is up and rotated 11 degrees to the right.
The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on Nov. 27, 2006 at a distance of approximately 2 million kilometres from Iapetus. Image scale is 12 kilometres per pixel.

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This image of Iapetus was taken by the Cassini spaceprobe on December 07, 2006, when it was approximately 2,869,479 kilometres away.

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Credit NASA/JPL

The image was taken using the CL1 and CL2 filters.

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This image of Iapetus was taken by the Cassini spaceprobe on November 27, 2006, when it was approximately 1,997,980 kilometres away.

Credit NASA

The image was taken using the CL1 and CL2 filters.

This image of Iapetus was taken by the Cassini spaceprobe on November 27, 2006, when it was approximately 1,998,833 kilometres away.

Credit NASA

The image was taken using the CL1 and IR3 filters.

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This image of Iapetus was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 6, 2006 at a distance of approximately 2.2 million kilometres from Iapetus and at a Sun- Iapetus-spacecraft, or phase, angle of 26 degrees.

The Image scale is 13 kilometres per pixel.
North on Iapetus (1,468 kilometres across) is up.

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The mysterious equatorial ridge on Saturn's moon Iapetus is either a fossil ring system that fell to the surface, or a pile up of crustal rocks formed as the satellite changed its shape. These are the latest theories from planetary scientists.
The ridge, revealed by the Cassini probe, is unlike anything else in the solar system. It is up to 20 kilometres high and stretches 1300 km along the moon's equator, resembling the ridge on a walnut.
Counts of impact craters show the ridge must be nearly as old as the crust on the adjacent plains, which are thought to have solidified about 4.5 billion years ago.
The first possible explanation for the ridge's formation is the slowing of Iapetus's spin from less than 10 hours per rotation when it formed to the present speed of 80 days.

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This Cassini spacecraft image shows the bright and dark regions on Iapetus. Some of the material that covers the moon's dark, leading side spills over into regions on the brighter trailing side, creating the feature near upper right referred to by some scientists as "the Moat."
The large impact basin above centre in the dark terrain has a diameter of about 550 kilometres.
This view looks toward the Saturn-facing hemisphere of Iapetus (1,468 kilometres across). North is up.

Credit NASA/JPL

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 25, 2006 at a distance of approximately 1.6 million kilometres from Iapetus. Image scale is 9 kilometres per pixel.

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This image of Iapetus was taken by the Cassini spaceprobe on June 25, 2006 when it was approximately 1,569,770 kilometres away.

The image was taken using the CL1 and CL2 filters.