S/2004 S 6

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S/2004 S 6
S2004 S6.jpg
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]
Epoch 13 April 2005 (JD 2453474.1)
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 < 5 km [1]
Rotation period probably synchronous
Axial tilt unknown
Albedo unknown
Atmosphere none

S/2004 S 6 is the designation of a dusty object seen orbiting Saturn very close to the F ring. It is not clear whether it is only a clump of dust, or if there is a solid small moon at its core.

It was first seen by scientists in pictures 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 area with at least five possible sightings in the period till late 2005. In comparison, two objects in the F ring's area (S/2004 S 3 and S/2004 S 4) that were first seen months earlier have not been found again 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 dust clump that will disappear in 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 find 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 sightings, however, with the discovery being made when the area 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 thinnest material around the F ring may have been a result of this.[3]

The dusty halo seen in pictures is big, being around 2000 km in lengthwise extent. The solid object, if any, would be no bigger than 3−5 km in diameter based on brightness.

References[change | edit source]

  1. 1.0 1.1 1.2 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. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006AJ....132..692S&db_key=AST&data_type=HTML&format=&high=444b66a47d06040.
  2. 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.)
  3. Charnoz, S.; et al. (2005). "Cassini Discovers a Kinematic Spiral Ring Around Saturn". Science 310: 1300. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Sci...310.1300C&db_key=AST&data_type=HTML&format=&high=444b66a47d06547.