Abstract:

Warps and vertical rifts or tears are frequently observed in protoplanetary disks and are also invoked to explain the rapid accretion of disk material onto supermassive black holes. Less well known outside of the planetary science community is the fact that the Cassini mission to Saturn observed several bending waves in Saturn’s rings that are resonantly excited by moons that move on orbits inclined relative to the ring plane.  Whereas warps in circumstellar disks are observed at low-resolution with a single viewing geometry, bending waves in Saturn’s rings have been observed by the Cassini spacecraft with excellent resolution at many different viewing geometries using stellar occultations.  Also, local N-body simulations of a warped planetary ring can be used to test theoretical models of warped disks.  Thus, Saturn’s rings provide a unique opportunity to improve our understanding of warped astrophysical disks.  Preliminary results show that (1) the vertical scale height of the ring increases with the warp amplitude of the ring plane, and (2) viscous damping of the vertically sheared horizonal motions in a bending wave can be more important than the traditional viscous damping.  A current research goal is to determine if a viscous instability can develop in nonlinear bending waves, which could explain the vertical rift observed in the Titan -1:0 nodal bending wave in Saturn’s C ring.

Speaker: Dr. Glen Stewart (Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder)

Host: Shigeru Ida, ELSI.

Date: Wed. 9 Oct. 16:00-17:00 JST

Venue: Mishima Hall, ELSI (hybrid)