The dark side of the rings of Uranus

• Main Authors: Imke De Pater, H B Hammel, Mark R Showalter, Marcos A Van Dam
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2007
• Subjects: South Pole; South pole
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1078.7413; http://www.flatwavefronts.com/uploads/papers/DarkSideRingsUranus.pdf

The rings of Uranus are oriented edge-on to Earth in 2007 for the first time since their 1977 discovery. This provides a rare opportunity to observe their dark (unlit) side, where dense rings darken to near invisibility, but faint rings become much brighter. We present a ground-based infrared image of the unlit side of the rings that shows that the system has changed dramatically since previous views. A broad cloud of faint material permeates the system, but is not correlated with the well-known narrow rings or with the embedded dust belts imaged by Voyager. Although some differences can be explained by the unusual viewing angle, we conclude that the dust distribution within the system has changed significantly since the 1986 Voyager spacecraft encounter and occurs on much larger scales than has been seen in other planetary systems. A planet's axial tilt causes an Earth-bound observer to see varying views as the planet travels around the Sun. Uranus has a tilt of 98°, so it presents extreme changes in viewing geometry during its 84-year orbit. The Voyager 2 encounter with Uranus in 1986 occurred near that planet's southern summer solstice-with its south pole pointed almost directly toward the Sun-so the rings were face-on and fully illuminated as Voyager approached (1). Twice during a Uranian year, the rings appear edge-on for a brief period, referred to as a ring plane crossing (RPX). We are currently in the midst of the first RPX since the rings were discovered in 1977