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TOPIC: Saturn's rings


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RE: Saturn Rings & Aldebaran
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The Cassini spacecraft took a series of images on Sept. 9, 2006 as it watched the bright red giant star Aldebaran slip behind Saturn's rings. This type of observation is known as a stellar occultation and uses a star whose brightness is well known. As Cassini watches the rings pass in front of the star, the star's light fluctuates, providing information about the concentrations of ring particles within the various radial features in the rings.

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Credit NASA

The view shows the Encke Gap (325 kilometres wide) and the faint ringlets which share the gap with the embedded moon Pan. The view looks toward the sunlit side of the rings from about 19 degrees below the ringplane. Bright Aldebaran is overexposed, creating thin vertical lines on its image.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 9, 2006 at a distance of approximately 359,000 kilometres from Saturn. Image scale on the sky at the distance of Saturn is 2 kilometres per pixel.

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Saturn F-ring
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This image of Saturns F-ring was taken by the Cassini spacecraft on October 07, 2006, when it was approximately 1,910,906 kilometres away.

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Credit NASA

The image was taken using the CL1 and CL2 filters.

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RE: Saturn Rings
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This image of Saturns rings was taken by the Cassini spaceprobe on September 26, 2006.

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Credit NASA

The image was taken using the CL1 and CL2 filters.

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G-Ring
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This image of Saturns' G-Ring was taken by the Cassini spacecraft on September 19, 2006, when it was approximately 2,180,684 kilometres away.

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The image was taken using the CL1 and CL2 filters.

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Janus/Epimetheus Ring
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The Cassini spacecraft has discovered a new ring around Saturn, in an image taken on Sunday, Sept. 17.

Other images captured by Cassini include wispy fingers of icy material stretching out tens of thousands of kilometres from the active moon, Enceladus, and a cameo colour appearance by planet Earth.
The images were obtained during the longest solar occultation of Cassini's four-year mission. During a solar occultation, the sun passes directly behind Saturn, and Cassini lies in the shadow of Saturn while the rings are brilliantly backlit. Usually, an occultation lasts only about an hour, but this time it was 12-hours.
Sunday's occultation allowed Cassini to map the presence of microscopic particles that are not normally visible across the ring system. As a result, Cassini saw the entire inner Saturnian system in a new light.

Sept17.2006
Credit NASA
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The view looks down from about 15 degrees above the un-illuminated side of the rings. Some faint spokes can also be spotted in the main rings, made visible by sunlight diffusing through the B ring.

The new ring is visible in this image (marked by a cross in the inset) outside the overexposed main rings and interior to the G and E rings. The G ring has a sharp inner boundary; the E ring is extremely broad and arcs across the upper and lower portions of the scene.
Scientists expected that meteoroid impacts on Janus and Epimetheus might kick particles off the moons' surfaces and inject them into Saturn orbit, but they were surprised that a well-defined ring structure exists at this location.
Saturn's extensive, diffuse E ring, the outermost ring, had previously been imaged one small section at a time. The 12-hour marathon enabled scientists to see the entire structure in one view. The moon Enceladus is seen sweeping through the E ring, extending wispy, fingerlike projections into the ring. These very likely consist of tiny ice particles being ejected from Enceladus' south polar geysers, and entering the E-ring.

"Both the new ring and the unexpected structures in the E ring should provide us with important insights into how moons can both release small particles and sculpt their local environments" - Matt Hedman, a research associate working with team member Joseph Burns, an expert in diffuse rings, at Cornell University in Ithaca, N.Y.

The image was taken in visible light with the Cassini spacecraft wide-angle camera on Sept. 15, 2006, at a distance of approximately 2.2 million kilometres from Saturn and at a sun-Saturn-spacecraft angle of almost 179 degrees. Image scale is 130 kilometres per pixel.

In the latest observations, scientists once again see the bright ghost-like spokes -- transient, dusty, radial structures -- streaking across the middle of Saturn's main rings.
Capping off the new batch of observations, Cassini cast its powerful eyes in our direction and captured Earth, a pale blue orb, and a faint suggestion of our moon. Not since NASA's Voyager 1 spacecraft saw Earth as a pale blue dot from beyond the orbit of Neptune has Earth been imaged in colour from the outer solar system.

"Nothing has greater power to alter our perspective of ourselves and our place in the cosmos than these images of Earth we collect from faraway places like Saturn. In the end, the ever-widening view of our own little planet against the immensity of space is perhaps the greatest legacy of all our interplanetary travels" - Carolyn Porco, Cassini imaging team leader at the Space Science Institute, Boulder, Colorado. Porco was one of the Voyager imaging scientists involved in taking the Voyager 'Pale Blue Dot' image.

In the coming weeks, several science teams will analyse data collected by Cassini's other instruments during this rare occultation event. The data will help scientists better understand the relationship between the rings and moons, and will give mission planners a clearer picture of ring hazards to avoid during future ring crossings.

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RE: Saturn Rings
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This image of spokes in Saturn's rings was taken by the Cassini spacecraft on September 15, 2006, when it was approximately 2,168,643 kilometres away.

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The image was taken using the IR3 and CL2 filters.

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This image of Saturn's rings was taken by the Cassini spacecraft on September 05, 2006 and received on Earth September 05, 2006, when it was approximately 2,092,767 kilometres away.

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The image was taken using the CL1 and CL2 filters.

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The F ring
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The clumpy disturbed appearance of the brilliant F ring constantly changes. The irregular structure of the ring is due, in large part, to the gravitational perturbations on the ring material by one of Saturn's moons, Prometheus (102 kilometres across).

F ring
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Credit NASA/JPL

Interior to the F ring, the A ring bears a striking resemblance to a classic grooved, vinyl record. Visible here are the Keeler gap (42 kilometres wide) and the Encke gap (325 kilometres wide).
The image was taken using a spectral filter sensitive to wavelengths of infrared light centred at 862 nanometers. The view was acquired with the Cassini spacecraft narrow-angle camera on July 26, 2006 at a distance of approximately 1.5 million kilometres from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 141 degrees. Image scale is 8 kilometres per pixel.

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The Encke gap
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The Encke gap displays gentle waves in its inner and outer edges that are caused by gravitational tugs from the small moon Pan. These scalloped edges were captured in an image taken by Cassini during its insertion into Saturn orbit in 2004.

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Credit NASA/JPL/Space Science Institute

The Encke gap is a 325-kilometer wide division in Saturn's outer A ring. Pan (26 kilometres across) orbits squarely in the centre of this gap.
The original image was stretched in the horizontal direction by a factor of four to exaggerate the amplitude of the waves, then reduced to half size and cropped to focus on the gap.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 23, 2006 at a distance of approximately 290,000 kilometres from Saturn. Scale in the original image was 1 kilometre per pixel.

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Opposition Effect
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This image of Saturn's A shows the opposition effect, a brightness surge that is visible on Saturn's rings when the Sun is directly behind the spacecraft.

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Credit NASA/JPL

The opposition effect exists because of two contributing factors. One is due to the fact that the shadows of ring particles directly opposite the Sun from Cassini -- the region of opposition -- fall completely behind the particles as seen from the spacecraft. These shadows are thus not visible to the spacecraft: all ring particle surfaces visible to the spacecraft in these two images are in sunlight and therefore bright. Much farther away from the region of opposition, the ring particle shadows become more visible and the scene becomes less bright. The brightness falls off in a circular fashion around the opposition point. The main factor to the opposition surge in this image is an optical phenomenon called "coherent backscatter." Here, the electromagnetic signal from the rays of scattered sunlight making its way back to the spacecraft is enhanced near the region of opposition because, instead of cancelling, the electric and magnetic fields comprising the scattered radiation fluctuate in unison.

The image was taken in visible light with the Cassini spacecraft wide-angle camera on July 23, 2006 at a distance of approximately 262,000 kilometres from Saturn. Image scale in the radial, or outward from Saturn, direction is 13 kilometres per pixel.

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