C. C. Porco, CICLOPS, Space Science Institute, Boulder; and the CassiniImaging Science Team (cf. IAUC 8389) report the discovery of S/2004 S 5, a satellite orbiting in the region of Saturn III (and Tethys) and Saturn IV (Dione). The new satellite was seen in a series of six consecutive narrow-angle, clear-filter frames taken on Oct. 21, spanning 3 hr; it was also seen in two wide-angle images taken 12 days later. The spread of observations around the orbit is too short to report the orbital distance and configuration with confidence; if S/2004 S 5 is in a near- equatorial and near-circulr orbit, it may be a coorbital satellite of Dione. S/2004 S 5 is approximately 5 km across. Also, S/2004 S 3 (cf. IAUC 8401) was recovered at phase angle 64 deg in a Cassini image taken on Oct. 17 (118 days after the discovery sequence of June 21). This puts the revolution period and semimajor axis at 0.62095 day and 140580 km. It is clear now that S/2004 S 3 is not the same object as S/2004 S 4 (IAUC 8401). Another object, S/2004 S 6, is also seen in the F-ring region, skirting the inner edge of the tenuous dust sheet that surrounds the F ring, in a sequence of movie images taken of that region at very high phase (153 deg) over a period of 1 hr on Oct. 28; its approximate orbital period and semimajor axis are 0.61 day and 140000 km. The fact that the object was seen at 153 deg phase may indicate that it is a clump with associated dust that is visible at high phase angles. It is possible, but not likely, that S/2004 S 6 is the same object as S/2004 S 4. More observations of this region, aimed at imaging orbiting satellites, are planned. A new narrow ring in the F-ring region, R/2004 S 2, is approximately 300 km wide and is located at 138900 km between the 'Atlas' ring (R/2004 S 1; IAUC 8401) and the orbit of Saturn XVI (Prometheus).
International Astronomical Union Circular
- Pub Date:
- November 2004