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Cassini Spacecraft Witnesses Saturn’s Blues

February 8, 2005

JPL — Colorful new images from the Cassini spacecraft show that Saturn’s northern hemisphere has a case of the blues.

In the first image, the icy moon Mimas is set against a dazzling and dramatic portrait of Saturn’s azure northern hemisphere and the shadows of its rings. A second image shows Saturn’s northern polar region is a dim blue.

The blue color of Saturn’s northern latitudes may to be linked to the apparently cloud-free nature of the upper atmosphere there. A precise understanding of the phenomenon may come from further study by Cassini imaging scientists.

In the first of these colorful views, Mimas moves in its orbit against the blue backdrop of Saturn’s atmosphere, which is draped by sweeping shadows cast by the rings. A few large craters are visible on Mimas, giving the icy moon a dimpled appearance.

The second view shows Saturn’s northern polar region, where shadows cast by the rings surrounding the pole appear as dark bands.

The ring shadows at higher latitudes correspond to locations on the ring plane that are farther from the planet – in other words, the northernmost ring shadow in this view is cast by the outer edge of Saturn’s A ring. Spots of bright clouds also are visible throughout the region.

The view of Saturn and Mimas was taken by the Cassini spacecraft’s narrow angle camera on Jan. 18, 2005, at a distance of approximately 1.4 million kilometers (870,000 miles) from Saturn. The view of Saturn’s northern polar region was taken with Cassini’s wide angle camera on Dec. 14, 2004, at a distance of 719,200 kilometers (446,900 miles) from Saturn.

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 Science Mission Directorate, Washington, D.C.

The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

Image Descriptions

Mimas Blues — Mimas drifts along in its orbit against the azure backdrop of Saturn’s northern latitudes in this true color view. The long, dark lines on the atmosphere are shadows cast by the planet’s rings.

Saturn’s northern hemisphere is presently relatively cloud-free, and rays of sunlight take a long path through the atmosphere. This results in sunlight being scattered at shorter (bluer) wavelengths, thus giving the northernmost latitudes their bluish appearance at visible wavelengths.

At the bottom, craters on icy Mimas (398 kilometers, or 247 miles across) give the moon a dimpled appearance.

Images taken using infrared (930 nanometers), green (568 nanometers) and ultraviolet (338 nanometers) spectral filters were combined. The colors have been adjusted to match closely what the scene would look like in natural color. See http://photojournal.jpl.nasa.gov/catalog/PIA06142 for a similar view in natural color.

The images were obtained using the Cassini spacecraft narrow angle camera on Jan. 18, 2005, at a distance of approximately 1.4 million kilometers (870,000 miles) from Saturn. Resolution in the image is 8.5 kilometers (5.3 miles) per pixel on Saturn and 7.5 kilometers (4.7 miles) per pixel on Mimas. The image has been contrast-enhanced to aid visibility.

Saturn’s Blue Cranium – Saturn’s northern hemisphere is presently a serene blue, more befitting of Uranus or Neptune, as seen in this natural color image from Cassini.

Light rays here travel a much longer path through the relatively cloud-free upper atmosphere. Along this path, shorter wavelength blue light rays are scattered effectively by gases in the atmosphere, and it is this scattered light that gives the region its blue appearance. Why the upper atmosphere in the northern hemisphere is so cloud-free is not known, but may be related to colder temperatures brought on by the ring shadows cast there.

Shadows cast by the rings surround the pole, looking almost like dark atmospheric bands. The ring shadows at higher latitudes correspond to locations on the ringplane that are farther from the planet — in other words, the northernmost ring shadow in this view is made by the outer edge of the A ring.

Spots of bright clouds also are visible throughout the region. This view is similar to an infrared image obtained by Cassini at nearly the same time (see http://photojournal.jpl.nasa.gov/catalog/PIA06567). The infrared view shows a great deal more detail in the planet’s atmosphere, however. Images obtained using red, green and blue spectral filters were combined to create this color view. The images were taken with the Cassini spacecraft wide angle camera on Dec. 14, 2004, at a distance of 719,200 kilometers (446,900 miles) from Saturn. The image scale is about 39 kilometers (24 miles) per pixel.

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On the Net:

NASA

Cassini-Huygens Mission


Cassini Spacecraft Witnesses Saturn8217s Blues


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