Non-circular features in Saturn%26apos;s D ring: D68

作者：Hedman M M^*; Burt J A; Burns J A; Showalter M R

来源：Icarus, 2014, 233: 147-162.

DOI：10.1016/j.icarus.2014.01.022

• Celestial mechanics
• Planetary rings
• Saturn, rings

D68 is a narrow ringlet located only 67,627 km (1.12 planetary radii) from Saturn%26apos;s spin axis. Images of this ringlet obtained by the Cassini spacecraft reveal that this ringlet exhibits persistent longitudinal brightness variations and a substantial eccentricity (ae = 25 +/- 1 km). By comparing observations made at different times, we confirm that the brightness variations revolve around the planet at approximately the local orbital rate (1751.6 degrees/day), and that the ringlet%26apos;s pericenter precesses at 38.243 +/- 0.008 degrees/day, consistent with the expected apsidal precession rate at this location due to Saturn%26apos;s higher-order gravitational harmonics. Surprisingly, we also find that the ringlet%26apos;s semi-major axis appears to be decreasing with time at a rate of 2.4 +/- 0.4 km/year between 2005 and 2013. A closer look at these measurements, along with a consideration of earlier Voyager observations of this same ringlet, suggests that the mean radius of D68 moves back and forth, perhaps with a period of around 15 Earth years or about half a Saturn year. These observations could place important constraints on both the ringlet%26apos;s local dynamical environment and the planet%26apos;s gravitational field.

• 出版日期2014-5-1