Satellites and Rings of Saturn

C. C. Porco, CICLOPS, Space Science Institute, Boulder; and the Cassini

Imaging 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).