* Astronomy

These two views of Iapetus primarily show terrain in the southern part of the moon's dark leading hemisphere -- the side of Iapetus that is coated with dark material. The bright South Pole of Iapetus is visible, along with some terrain (at the bottom) that lies on the bright trailing hemisphere.

The dark terrain known as Cassini Regio is uniformly dark between the equator and about 30 degrees south latitude. From there down to about 50 to 60 degrees south latitude, the dark material looks "patchy" because south-facing crater walls are bright (being largely devoid of the dark material). South of this region, only some northward-facing crater walls are still dark, while the bright terrain has a somewhat reddish colour.


Credit NASA

Beyond 90 degrees south (i.e., on the trailing side), the reddish colour becomes white. The region at the bottom of the colour view presented here shows this "colour boundary" in the bright terrain, which also marks the boundary between the leading and trailing hemispheres.

North is up in the monochrome image and rotated 16 degrees to the left in the colour image.
The monochrome image on the left was taken using a filter sensitive to wavelengths of infrared light centred at 930 nanometers. The image was obtained with the Cassini spacecraft narrow-angle camera on April 8, 2006, at a distance of approximately 866,000 kilometres from Iapetus and at a Sun-Iapetus-spacecraft, or phase, angle of 88 degrees. The image scale is 5 kilometres per pixel.
The colour view on the right was created by combining images taken in ultraviolet, green and infrared spectral filters. The images were acquired with the Cassini spacecraft narrow-angle camera on April 9, 2006, at a distance of approximately 692,000 kilometres from Iapetus and at a Sun-Iapetus-spacecraft, or phase, angle of 101 degrees. The image scale is 4 kilometres per pixel.

This is another view of the previous posts.

Sunlight strikes the terminator region on Saturn's moon Iapetus at nearly horizontal angles, making visible the vertical relief of many features.



This view is centred on terrain in the southern hemisphere of Iapetus. Lit terrain visible here is on the moon's leading hemisphere. In this image, a large, central-peaked crater is notable at the boundary between the dark material in Cassini Regio and the brighter material on the trailing hemisphere.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 22, 2006, at a distance of approximately 1.3 million kilometres from Iapetus and at a Sun-Iapetus-spacecraft, or phase, angle of 67 degrees. Resolution in the original image was 8 kilometres per pixel. The image has been magnified by a factor of two and contrast-enhanced to aid visibility.

This image shows Cassini Regio on Iapetus as well as the equatorial ridge that bisects the terrain, curving along the lower left edge of Iapetus.

The view looks down onto the northern hemisphere of Iapetus, and shows terrain on the moon's leading hemisphere.


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The image was taken in polarized green light with the Cassini spacecraft narrow-angle camera on Nov. 12, 2005 at a distance of approximately 417,000 kilometres from Iapetus and at a Sun-Iapetus-spacecraft, or phase, angle of 95 degrees. Image scale is about 2 kilometres per pixel.

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This image was taken on November 12, 2005 by the Cassini spacecrsft of Iapetus that was approximately 418,482 kilometres away. The image was taken using the CL1 and IR1 filters.


Negative image.
Credit NASA