Self-gravity and viscous overstability: Dynamical and photometric modelling of the fine structure in Saturn’s rings
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
Auditorium L6, Linnanmaa campus, University of Oulu
Topic of the dissertation
Self-gravity and viscous overstability: Dynamical and photometric modelling of the fine structure in Saturn’s rings
Doctoral candidate
Master of Science (MSc) Annabella Elizabeth Mondino Llermanos
Faculty and unit
University of Oulu Graduate School, Faculty of Science, Space physics and astronomy
Subject of study
Astronomy
Opponent
Professor Philip Nicholson, Cornell University
Custos
Professor Heikki Salo, University of Oulu
The effect of mutual collisions and gravitational forces of ring particles on the formation of the fine structure of Saturn's rings
This dissertation explores the dynamics of Saturn's rings, focusing on how mutual interactions between ring particles shape the fine structure of the rings. The study examines two primary types of interactions: gravitational interactions between particles and their partially elastic collisions. These physical processes influence the motion of the particles and lead to a non-uniform density distribution within the ring.
Although the scale of the resulting fine structure lies below the resolution of observations, photometric modeling enables comparisons between the global phenomena caused by these processes and observations of Saturn's rings from Earth-based telescopes and space probes. The research focuses on the following phenomena:
1. Gravitationally induced density enhancements ("self-gravity wakes"): These are filament-like density structures caused by the mutual gravity of ring particles. While individual enhancements form and dissipate over short timescales, models predict a specific average strength and orientation of these enhancements relative to the radial direction.
2. Oscillatory instability ("viscous overstability"): These are axially symmetric density variations that occur when the ring's viscosity increases sharply with density. In such cases, collisions cause small density oscillations to spontaneously amplify.
To study these phenomena, we developed a new computer simulation tool suitable for use in multiprocessor environments. This tool tracks the motion of ring particles over time, modeling their gravitational interactions and collisions. Using this simulation tool, we examine how these processes collectively influence the ring's structure. Notably, we have identified the conditions under which oscillatory instability arises.
The research also analyzes observed properties of Saturn's rings by using synthetic images and optical depth profiles generated by the simulations. The results suggest that the size distribution of ring particles plays a central role in the local fine structure of the rings. Furthermore, the study constrains other physical properties of the ring particles. An especially intriguing finding is that the internal density of ring particles is significantly lower than that of water ice under terrestrial conditions.
Although the scale of the resulting fine structure lies below the resolution of observations, photometric modeling enables comparisons between the global phenomena caused by these processes and observations of Saturn's rings from Earth-based telescopes and space probes. The research focuses on the following phenomena:
1. Gravitationally induced density enhancements ("self-gravity wakes"): These are filament-like density structures caused by the mutual gravity of ring particles. While individual enhancements form and dissipate over short timescales, models predict a specific average strength and orientation of these enhancements relative to the radial direction.
2. Oscillatory instability ("viscous overstability"): These are axially symmetric density variations that occur when the ring's viscosity increases sharply with density. In such cases, collisions cause small density oscillations to spontaneously amplify.
To study these phenomena, we developed a new computer simulation tool suitable for use in multiprocessor environments. This tool tracks the motion of ring particles over time, modeling their gravitational interactions and collisions. Using this simulation tool, we examine how these processes collectively influence the ring's structure. Notably, we have identified the conditions under which oscillatory instability arises.
The research also analyzes observed properties of Saturn's rings by using synthetic images and optical depth profiles generated by the simulations. The results suggest that the size distribution of ring particles plays a central role in the local fine structure of the rings. Furthermore, the study constrains other physical properties of the ring particles. An especially intriguing finding is that the internal density of ring particles is significantly lower than that of water ice under terrestrial conditions.
Last updated: 3.1.2025