Article Summary #14

Saturn's largest ring

A. J. Verbiscer, M. F. Skrutskie, D. P. Hamilton, 2009, Nature 461, 1098-1100
http://www.nature.com/nature/journal/v461/n7267/full/nature08515.html

By analyzing data from the Spitzer Space Telescope’s MIPS (multi-band imaging photometer), Verbiscer et al. 2009 conducted an investigation on one of Saturn’s satellites, Phoebe, in order to look for a broad debris disk. A debris disk is a circumstellar disk of dust and debris in orbit around a star and can constitute a phase in the formation of a planetary system following the protoplanetary disk phase.

By looking at mid-infrared images of Saturn’s ecliptic plane, Verbiscer et al. 2009 detected a diffused band of light with two peaks which they knew did not come from the planet’s scattered light.

In most cases, the moon of a planet continuously supplies dust to a planetary ring associated with it, but this has been observed for the satellites that are closest to their planets. In this paper, Verbiscer et al. 2009 discuss the discovery of a ring of this type for Phoebe. This phenomenon is very unusual because Phoebe is very far from its hosting planet (a distance hundreds of times greater than the radius of Saturn), and the disk appears to be ~40 times thicker than the same radius and matches the satellite’s orbit and its vertical range.

This ring has not been detected before due to the fact that its composed out of particles smaller than 1cm and the impacts on Phoebe are the main material supplement for the ring. Its dispersion, which for other rings is know to be equatorial, was observed as symmetric about Saturn’s plane orbit.

Lastly, Verbiscer et al. 2009 noticed a similarity between Phoebe and its ring: they have retrograde orbits which are different from other moon-ring systems with a counter-clockwise orbit.