Summary: The Astrophysical Journal Letters, 718:L176­L180, 2010 August 1 doi:10.1088/2041-8205/718/2/L176
C 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
DIRECT EVIDENCE FOR GRAVITATIONAL INSTABILITY AND MOONLET FORMATION IN SATURN's
RINGS
K. Beurle, C. D. Murray, G. A. Williams, M. W. Evans1
, N. J. Cooper, and C. B. Agnor
Astronomy Unit, Queen Mary University of London, Mile End Road, London E1 4NS, UK; C.D.Murray@qmul.ac.uk
Received 2010 March 3; accepted 2010 June 30; published 2010 July 14
ABSTRACT
New images from the Cassini spacecraft reveal optically thick clumps, capable of casting shadows, and associated
structures in regions of Saturn's F ring that have recently experienced close passage by the adjacent moon
Prometheus. Using these images and modeling, we show that Prometheus' perturbations create regions of enhanced
density and low relative velocity that are susceptible to gravitational instability and the formation of distended,
yet long-lived, gravitationally coherent clumps. Subsequent collisional damping of these low-density clumps may
facilitate their collapse into 10­20 km contiguous moonlets. The observed behavior of the F ring is analogous to
the case of a marginally stable gas disk being driven to instability and collapse via perturbations from an embedded
gas giant planet.
Key words: instabilities ­ planets and satellites: dynamical evolution and stability ­ planets and satellites:
formation ­ planets and satellites: rings ­ planet­disk interactions
1. INTRODUCTION

Source: Agnor, Craig B. - Astronomy Unit, School of Mathematical Sciences, Queen Mary, University of London

Collections: Physics