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TOPIC: Rhea Spot
Blobrana


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RE: Rhea Spot
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One of the more exciting discoveries made by Cassini at Saturn is the possible presence of a ring around one of its moons, Rhea. Evidence for a ring around Rhea comes from the Magnetospheric Imaging Instrument (MIMI); Cassini saw symmetric drops in the flow of electrons around Rhea, and one possible explanation for such a pattern is the presence of big chunks of ice in Rhea's orbit that physically block the free flow of electrons through Saturn's plasma environment. Unfortunately, the particles would be too big to scatter light the way Saturn's dusty rings do, but too small to be individually visible to Cassini's cameras, so there didn't seem to be any way for Cassini to confirm or refute this intriguing idea.

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Blobrana


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This image of a bright ray crater on the southern portions of Rhea's leading hemisphere was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 26, 2008 at a distance of approximately 463,000 kilometres from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 58 degrees.

PIA10533.jpg
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Credit: NASA/JPL/Space Science Institute

The impact that produced the bright rays excavated material from below the surface which is brighter than the surrounding terrain on which it fell.
Image scale is 3 kilometres  per pixel.

-- Edited by Blobrana at 16:01, 2008-12-12

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Blobrana


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rhea170708b.jpg
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Credit NASA/JPL/Space Science Institute

This image of Rhea was taken by the Cassini spacecraft on July 17, 2007 at a distance of approximately 1.2 million kilometres away
This view looks toward the unilluminated side of the rings from less than a degree above the ringplane.
A dark line from Saturn's ringplane and the planet's atmosphere is seen in the background.
Image scale is 7 kilometres per pixel.

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Blobrana


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This view of Saturn's moon Rhea shows two large ancient impact basins and a recent, bright ray crater.
The large basin above centre is named Tirawa. This feature is overprinted by many other craters, meaning it is an extremely old feature.
This bright ray crater appears to be a younger feature, as it possesses crisp edges, is not heavily overprinted by other craters, and the blanket of bright, fresh material thrown out by the impact is still visible.

RheaMay1308
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Credit: NASA/JPL/Space Science Institute

North on Rhea is toward the top of the image. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on May 13, 2008, when it was approximately 889,000 kilometres away, and at a Sun-Rhea-spacecraft, or phase, angle of 31 degrees.

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Blobrana


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Rhea
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This image of the south polar region of Rhea was taken with the Cassini spacecraft narrow-angle camera on April 12, 2008 using a spectral filter sensitive to wavelengths of ultraviolet light centred at 338 nanometers, when the probe was approximately 345,000 kilometres from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 73 degrees.
Image scale is 2 kilometres per pixel.

rheaApril1208
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Credit: NASA/JPL/Space Science Institute

Images shown that Saturn's second-largest moon is not differentiated, or separated into distinct layers; instead, it appears to be a mixture of approximately 75 percent ices and 25 percent rock and metal.

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Blobrana


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RE: Rhea Spot
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This image of Rhea's northern regions was taken by the Cassini spacecraft in visible light using the narrow-angle camera on March 20, 2008, when it was at a distance of approximately 1.1 million kilometres away, and at a Sun-Rhea-spacecraft, or phase, angle of 74 degrees.

rhea2
Expand (25kb, 1024 x 768)
Credit NASA

The moon's Tirawa impact basin can be seen near the centre.
Image scale is 6 kilometres per pixel.

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Blobrana


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Rhea, Godly Mother of all Moons



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Blobrana


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Cassini found no trace of rings around Saturns similar icy moons Dione and Tethys, which Jones speculates cannot hold onto rings because they are much closer to Saturn than Rhea and therefore subject to more interference from the planets gravity.
Normally, narrow rings require a small moon to shepherd the particles and keep them confined, but no satellites of Rhea have been spotted so far.
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Blobrana


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Rhea May Also Have Rings
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NASA's Cassini spacecraft has found evidence of material orbiting Rhea, Saturn's second largest moon. This is the first time rings may have been found around a moon.
A broad debris disk and at least one ring appear to have been detected by a suite of six instruments on Cassini specifically designed to study the atmospheres and particles around Saturn and its moons.

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Blobrana


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Rhea Ring
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For the first time, scientists believe they have uncovered evidence for a moon to have its own ring system.  During a flyby of Saturn's second-largest moon Rhea on November 26, 2005, Cassini's Magnetospheric Imaging Instrument (MIMI) found that something unseen was blocking the flow of electrons in Rhea's neighbourhood.  Detailed analysis of the data suggests that the unseen something is a sparse, rocky disk of material orbiting Rhea's equator -- a system of rings orbiting a moon that itself orbits the ringed planet Saturn.

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