S/2004 S 6
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 object seen on 21 June 2005 by Cassini, thought to be S/2004 S 6 |
|
| Discovery | |
|---|---|
| Discovered by | Cassini Imaging Science Team |
| Discovered on | 28 October 2004 |
| Orbital characteristics[1] | |
|
|
|
| Semimajor axis | 140,134 ± 2 km |
| Eccentricity | 0.00200 ± 0.00004 |
| Revolution period | 0.6180116 ± 0.0000004 d |
| Inclination to Saturn's equator |
0.002 ± 0.001° |
| Is a satellite of | Saturn |
| Physical characteristics | |
| Mean diameter | < 5km [1] |
| Rotation period | probably synchronous |
| Axial tilt | unknown |
| Albedo | unknown |
| Atmosphere | none |
S/2004 S 6 is the provisional designation of a dusty object seen orbiting Saturn very close to the F ring. It is not clear whether it is only a transient clump of dust, or if there is a solid moonlet at its core.
It was first seen by scientists in images taken by the Cassini-Huygens probe on October 28, 2004, and announced on 8 November that year.[2] It appears to be the best tracked object in this region with at least five probable sightings in the period till late 2005. In comparison, two objects in the F ring's vicinity (S/2004 S 3 and S/2004 S 4) that were first seen several months earlier have not been recovered with any confidence. Nevertheless, it continues to be unclear whether there is a solid core to S/2004 S 6 or whether it is just a transient dust clump that will dissipate on a timescale of years or months. Notably, an imaging sequence covering an entire orbital period at 4 km resolution taken on 15 November 2004 (soon after S/2004 S 6's discovery) failed to recover the object, while it has been seen again later. The lighting conditions in S/2004 S 6's part of the orbit were different during these two observations, however, with the discovery being made when the region was strongly backlit by the sun. A suggested resolution of the absence in November is that S/2004 S 6's visibility is primarily due to a diffuse cloud of fine dust that is much brighter in forward scattered light (the conditions of the discovery image), and that the solid core (if any) is small.[1]
S/2004 S 6 has been seen both inside and outside the main F ring, and its orbit must cross the ring. Careful calculations show that the object periodically plows through the ring material, coming within 1.5 km of the densest core e.g. on 9 April 2005. It has been suggested that a spiral structure in the tenuous material surrounding the F ring may have been a consequence of this.[3]
The dusty halo seen in images is sizeable, being around 2000 km in lengthwise extent. The solid object, if any, would be no greater than 3−5 km in diameter based on brightness.
Additional evidence came in 2008, as it appears that S/2004 S 6 or a body like it is required to explain additional the dynamics of the F Ring.[4]
[edit] References
- ^ a b c Spitale, J. N.; et al. (2006). "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations". The Astronomical Journal 132: 692. doi:.
- ^ IAUC 8432: Satellites and Rings of Saturn 2004 November 8 (claiming recovery of S/2004 S 3 on 17 October 2004, in conflict with the later (2006) Spitale et al.)
- ^ Charnoz, S.; et al. (2005). "Cassini Discovers a Kinematic Spiral Ring Around Saturn". Science 310: 1300. doi:.
- ^ "The determination of the structure of Saturn's F ring by nearby moonlets" Carl D. Murray, Kevin Beurle, Nicholas J. Cooper, Michael W. Evans, Gareth A. Williams & Sébastien Charnoz. Nature, 5 June 2008.
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