Circular No. 9023 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions) CBAT@CFA.HARVARD.EDU (science) URL http://www.cfa.harvard.edu/iau/cbat.html ISSN 0081-0304 Phone 617-495-7440/7244/7444 (for emergency use only)
S/2008 S 1 C. C. Porco, on behalf of the Cassini Imaging Science Team, reports the discovery of S/2008 S 1, an object orbiting within Saturn's G ring in the region between Saturn X/XI (Janus/Epimetheus) and Saturn I (Mimas), in two images of the G ring obtained with Cassini's narrow-angle camera taken on 2008 Aug. 15 and separated by approximately 30 min. Subsequent observations, and a search of earlier images based on a preliminary orbit fit, have provided additional detections of this object, yielding 21 total detections during 2007 June 15-2009 Feb. 20. A high-precision orbit fit based on a numerical integration of the equations of motion shows that the object is being influenced by a 7:6 mean-motion resonance with Mimas; averaged orbital elements for S/2008 S 1: a = 167500 km; e = 0.0002, i = 0.001 deg, revolution period = 0.80812 day. The integrated orbit shows that the resonance with Mimas causes a long-period (about 4 yr) oscillation of about 4 km in the semi-major axis of S/2008 S 1, with a corresponding oscillation of a few degrees in its mean longitude. S/2008 S 1 is located within a bright arc in the G ring, so this body likely represents a significant source of the small particles found in this ring. If S/2008 S 1 has the same disk-integrated reflectivity as Saturn XXXIII (Pallene), preliminary estimates of the object's total brightness suggest a physical radius for S/2008 S 1 of about 250 m.
(C) Copyright 2009 CBAT 2009 March 3 (9023) Daniel W. E. Green