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Four New Saturn Satellites Discovered
IAU Circular 6192


Congratulation to Amanda Bosh and Andrew Rivkin who have announced their discovery of four new possible satellites of Saturn in IAU Circular 6192 (see below). The new satellites were detected using the Hubble Space Telescope's Wide Field Planetary Camera II during the May 22 Saturn ring plane crossing. The new moons have diameters ranging from 19 to 34 miles. One of the moons, tentatively named 1995 S3, is apparently a shepherd moon for the F ring since it orbits just outside of the ring. There are already two known moon shepherds for the F Ring, Prometheus and Pandora, and the discovery of a third shepherding moon may account for the unusual braiding observed in Voyager images of the F Ring.

blue_dot.gif HST's Planned WF/PC Observations of the May Ring Plane Crossing
blue_dot.gif Hubble Image of a New Saturn Moon

Ron Baalke

Note: Permission has been obtained from Brian Marsden to place this IAU Circular on this home page. For more information on IAU Circulars, see the Central Bureau for Astronomical Telegrams home page, and also look at CBAT's Circular Distribution Policy.

IAU Circular 6192

Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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A. S. Bosh, Lowell Observatory; and A. S. Rivkin, Lowell Observatory and Lunar and Planetary Laboratory, report: "We have discovered four probable satellites of Saturn, from twenty-seven 400-s images taken in the 890-nm methane band with the HST Wide Field Planetary Camera 2 during an 11-hr span at the May 22 ring- plane crossing. For each satellite, we give below the orbital radius; the angular distance from Saturn at May 22.48584 UT (negative values indicating that the satellite is west of Saturn); the longitude at the same epoch (measured from the sub-earth point); the approximate V magnitude at opposition; and the number of images in which the satellite was detected: S/1995 S 1, 137450 +/- 200 km, -16".4, +120 deg, 17.2, 15; S/1995 S 2, 139700 +/- 300 km, -18".0, +69 deg, 16.3, 12; S/1995 S 3, 141050 +/- 100 km, -10".5, +33 deg, 17.5, 14; S/1995 S 4, 146450 +/- 450 km, +14".2, -44 deg, 18.3, 11. S/1995 S 1, S 2, and S 3 were identified in each frame in which they were not close to Saturn or a bright satellite. S/1995 S 4 was not identified in seven frames in which it should have been visible, all before ring-plane crossing, when the background noise was higher. Satellite positions were fitted to a circular orbit in the plane of the rings, including terms arising from Saturn's nonspherical gravity field. Maximum residuals were in all cases < 0".5, and for S/1995 S 2 and S 3 were no greater than 0".15, which is approximately the centering error. All known satellites are accounted for except Saturn XVIII (Pan), XV (Atlas), and XVI (Prometheus), which may be visible but are still uncertain; the possibility exists that S/1995 S 1 is Atlas and that S/1995 S 2 is Prometheus, although they would be 26 and 21 deg from their respective predicted positions. We see no satellites outside the rings (the distance of which from Saturn at the times of observation was > 20") with opposition V mag equal to or brighter than 19, i.e., that of Saturn XIV (Calypso)."

1995 July 26 (6192) Daniel W. E. Green

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