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TOPIC: 60 Saturn moons


L

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RE: S/2004 S6
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This montage of four enhanced Cassini narrow-angle camera images shows bright clump-like features at different locations within Saturns F ring.

Two objects in particular, provisionally named S/2004 S3 and S/2004 S6, have been repeatedly observed by Cassini over the past 13.5 months and 8.5 months, respectively. The orbits for these two objects have not yet been precisely determined, in part because perturbations from other nearby moons make the orbits of objects in this region complicated. Thus, scientists cannot be completely confident at the present time if they in fact have observed new sightings of S3 and S6, or additional transient clumps.


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The upper two images show features that may be S6. From previous observations, S6 appears to have an orbit that crosses that of the main F ring. This unexpected behaviour currently is a subject of great interest to ring scientists.
The upper left image was taken on June 21, 2005, and shows an object in the outer ringlets of the F ring. The radial (or lengthwise) extent of the feature is approximately 2,000 kilometres. The radial resolution on the ring is about 13 kilometres per pixel.

The image at the upper right was taken on June 29, 2005, and shows a bright feature within the F ring's inner ringlets. The radial extent of the feature seen here is about 2,000 kilometres (1,200 miles); the radial resolution is 36 kilometres.

The image at the lower left was taken on August 2, 2005, and shows a feature that may be S3. S3 has been found to have an orbital path that is tightly aligned with that of the main F ring. The radial resolution in the image is 3.5 kilometres per pixel.
The lower right image was taken on April 13, 2005, and has a radial resolution of 7 kilometres per pixel. This object does not appear to be either S3 or S6.

Structures like knots and clumps within the F ring often are transient, appearing and then disappearing within months. Repeated observation of the objects seen in this region hopefully will give scientists firm evidence about whether these features are actual moons that disturb the material around them or perhaps the short-lived products of interactions between the F ring and larger moons such as Prometheus.

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L

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RE: 46 Saturn moons
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The Cassini spacecraft has confirmed earlier suspicions of an unseen moon hidden in a gap in Saturn's outer A ring. A new image and movie show the new moon and the waves it raises in the surrounding ring material.

The moon, provisionally named S/2005 S1, was first seen in a time- lapse sequence of images taken on May 1, 2005, as Cassini began its climb to higher inclinations in orbit around Saturn. A day later, an even closer view was obtained, which has allowed a measure of the moon's size and brightness.
The tiny object is located in the centre of the Keeler gap and the wavy patterns in the gap edges that are generated by the moon's gravitational influence. The Keeler gap is located about 250 kilometres inside the outer edge of the A ring, which is also the outer edge of the bright main rings.


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The new object is about 7 kilometres across and reflects about half the light falling on it -- a brightness that is typical of the particles in the nearby rings.
"It's too early to make out the shape of the orbit, but what we've seen so far of its motion suggests that it is very near the exact centre of the gap, just as we had surmised." - Dr. Joseph Spitale, imaging team associate and planetary scientist at the Space Science Institute in Boulder, Colo.

The new moonlet orbits approximately 136,505 kilometres from the centre of Saturn.
S/2005 S1 is the second known moon to exist within Saturn's rings. The other is Pan, 25 kilometres across, which orbits in the Encke gap. Atlas and other moons exist outside the main ring system, as do the two F ring shepherd moons, Prometheus and Pandora.
Imaging scientists had predicted the new moon's presence and its orbital distance from Saturn after last July's sighting of a set of peculiar spiky and wispy features in the Keeler gap's outer edge. The similarities of the Keeler gap features to those noted in Saturn's F ring and the Encke gap led imaging scientists to conclude that a small body, a few kilometres across, was lurking in the centre of the Keeler gap, awaiting discovery.
An estimate of the moon's mass, along with a measure of its size, yields information on its physical makeup. For instance, the new moonlet might be quite porous, like an orbiting icy rubble pile. Other moons near the outer edge of Saturn's rings - like Atlas, Prometheus and Pandora - are also porous. Whether a moon is porous or dense says something about how it was formed and its subsequent collision history.
The Keeler gap edges also bear similarities to the scalloped edges of the 322-kilometer-wide Encke gap, where the small moon Pan (25 kilometres across) resides. From the size of the waves seen in the Encke gap, imaging scientists were able to estimate the mass of Pan. They expect to do the same eventually with this new moon.

"Some of the most illuminating dynamical systems we might hope to study with Cassini are those involving moons embedded in gaps. By examining how such a body interacts with its companion ring material, we can learn something about how the planets in our solar system might have formed out of the nebula of material that surrounded the Sun long ago. We anticipate that many of the gaps in Saturn's rings have embedded moons, and we'll be in search of them from here on." - Dr. Carolyn Porco, imaging team leader at the Space Science Institute.



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L

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60 Saturn moons
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Astronomers have discovered 12 new moons orbiting Saturn, bringing its number of natural satellites to 46.
The moons are small, irregular bodies - probably only about 3-7km in size (assuming they have a surface albedo of 4%) - that are far from Saturn and take about two years to complete one orbit.


moon S2004 S11

All but one circles Saturn in the opposite direction to its larger moons (a characteristic of captured bodies).
Jupiter is the planet with the most moons, 63 at the last count; Saturn now has 46. Uranus has 27 and Neptune 13.
The latest satellites were discovered on December 12, 2004 using the wide-field SuprimeCam camera on the 8.2-meter diameter Subaru telescope on Mauna Kea, Hawaii. Confirmation observations were made using the Gemini North telescope, also situated in Hawaii.
The newly-found satellites were probably formed in the main asteroid belt between Mars and Jupiter, and scattered out of it by the tug of Jupiter's gravity.



-- Edited by Blobrana at 22:54, 2007-07-19

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