S/2004 S 6
From Wikipedia, the free encyclopedia
 object seen on 21 June 2005 by Cassini, thought to be S/2004 S 6 |
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| Discovery | |
|---|---|
| Discovered by | Cassini Imaging Science Team |
| Discovered on | 28 October 2004 |
| Orbital characteristics [1] | |
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| 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 5 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 S6 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 S6's discovery) failed to recover the object, while it has been seen again later. The lighting conditions in S6'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 S6'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].
S6 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.
[edit] References
- ^ a b c J.N. Spitale et al (2006). "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations". The Astronomical Journal 132: 692.
- ^ IAUC 8432
- ^ S. Charnoz et al (2005). "Cassini Discovers a Kinematic Spiral Ring Around Saturn". Science 310: 1300.
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Generally listed in increasing distance from Saturn
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| Ring shepherds | Pan · Daphnis · Atlas · Prometheus · S/2004 S 6? · S/2004 S 4? · S/2004 S 3? · Pandora |
| Co-orbitals | Epimetheus · Janus |
| Inner large and Trojan | Mimas · Methone · Pallene · Enceladus · Tethys (trojans Telesto, Calypso) · Dione (trojans Helene, Polydeuces) |
| Outer large | Rhea · Titan · Hyperion · Iapetus |
| Inuit group | Kiviuq · Ijiraq · Paaliaq · Siarnaq |
| Norse group | Phoebe · Skathi · Skoll · S/2004 S 13 · S/2006 S 4 · Hyrokkin · Mundilfari · S/2006 S 6 · S/2006 S 1 · S/2004 S 17 · Narvi · Bergelmir · Aegir · Suttungr · S/2004 S 12 · Bestla · Farbauti · Hati · S/2004 S 7 · Thrymr · S/2006 S 3 · Surtur · Kari · Fenrir · Ymir · Loge · Fornjot |
| Gallic group | Albiorix · Bebhionn · Erriapo · Tarvos |
