Hedman, M. M., Burns, J. A., Tiscareno, M. S., Nicholson, P. D., Porco, C. C., Jones, G. H., Roussos, E., Krupp, N., Paranicas, C. (2006). "Multi-instrument studies of an Arc in Saturn's G Ring." Eos Trans. AGU 87(52), Fall Meet. Suppl., Abstract P23E-0111 I.


Abstract

The G ring is a narrow, faint ring located between the orbits of Janus and Mimas. The first evidence for material in this region came from a series of charged particle absorptions detected by Pioneer 11 in 1979, and the ring itself was first imaged by the Voyager spacecraft. Now a combination of in-situ and optical remote sensing instruments onboard the Cassini spacecraft are providing new insights into the dynamics and origin of this obscure ring. During a pass over the G ring on day 248 of 2005, the MIMI instrument detected a deep, narrow charged particle absorption signature in the vicinity of the G ring. Similarly deep and narrow charged particle absorptions were not seen during Cassini's other passages near this region. The magnitude of the charged particle absorption on day 248 suggested either the presence of a solid body or a much higher particle density in the G ring than one might expect from other observations. Images obtained by the cameras onboard Cassini reveal that the likely explanation for this anomaly is a bright arc located on the inner edge of the G ring (around 167,500 km) and extending over 30 degrees in longitude. By tracking this arc over the first two years of the Cassini Missi7on, we have established that Cassini passed close to the arc on day 248 of 2005, and that Cassini was not near the arc during other passages near the G ring. The orbital period of the arc is 0.80813 day, corresponding to a semi-major axis of 167,496 km. This places the arc within 6 km of the Mimas 7:6 Co-rotation Eccentricity Resonance and within 12 km of the Mimas 7:6 Inner Lindblad Resonance. The arc is therefore likely confined in longitude by Mimas in the same way that the arcs in Neptune's ring are held in place by Galatea. Cassini now has the opportunity to study the dynamics of this sort of system in detail over a period of years. The arc may also be the source of the material for the rest of the G ring. A combination of photometric and spectroscopic data from optical remote sensing instruments and in-situdata from MIMI should also provide constraints on the density and particle size distribution of this arc.