Noncircular features in Saturn鈥檚 rings I: The edge of the B ring

详细信息    查看全文

• 作者：Philip D. Nicholson ; Richard G. French ; Matthew M. Hedman ; Essam A. Marouf ; Joshua E. Colwell
• 关键词：Occultations ; Planetary rings ; Saturn ; rings
• 刊名：Icarus
• 出版年：1 January, 2014
• 年：2014
• 卷：227
• 期：Complete
• 页码：152-175
• 全文大小：2801 K

文摘

A comprehensive investigation of all available radio and stellar occultation data for the outer edge of Saturn鈥檚 B ring, spanning the period 1980-2010, confirms that the m = 2 distortion due to the strong Mimas 2:1 inner Lindblad resonance circulates slowly relative to Mimas in a prograde direction, with a frequency 惟_L = 0.1819掳 d^鈭?. Our best-fitting model implies that the radial amplitude of this distortion ranges from a minimum of 3 km to a maximum of 71 km, with short-lived minima recurring every 5.42 yrs. In addition to the dominant m = 2 pattern, the edge of the B ring also exhibits at least four other perturbations. An m = 1 component with a radial amplitude of 鈭?0 km rotates at a rate very close to the expected local apsidal precession rate of  d^鈭?, while smaller perturbations are seen with m = 3 (amplitude 12.5 km), m = 4 (5.9 km), and m = 5 (5.6 km), each of which has a pattern speed consistent with that expected for a spontaneously-generated 鈥渘ormal mode鈥?(French, R.G. et al. [1988]. Icarus 73, 349-378). Our results for m = 1, m = 2 and m = 3 are compatible with those obtained by Spitale and Porco (Spitale, J.N., Porco, C.C. [2010]. Astron. J. 140, 1747-1757), which were based on Cassini imaging data. The pattern speed of each normal mode slightly exceeds that expected at the mean edge radius, supporting their conclusion that they may represent a series of free modes, each of which is trapped in a narrow region between the mode鈥檚 resonant radius and the ring鈥檚 edge. However, both our model and that of Spitale and Porco fail to provide complete descriptions of this surprisingly complex feature, with post-fit root-mean-square residuals of 鈭? km considerably exceeding typical measurement errors of 1 km or less.