NASA/ESA

Dynamics of planetary rings and galaxies

Research is lead by prof. Heikki Salo.

The current research topics of our group include:

  • Planetary ring dynamics
  • Satellite resonances
  • Dynamics and observations of interacting galaxies
  • Dynamics of barred galaxies
  • Development of numerical N-body simulation methods

The most important current collaborations are with the University of Alabama (Ron Buta), the Wellesley College (Richard French), and the University of Potsdam (Jürgen Schmidt, Frank Spahn).

Our recent planetary ring studies have concentrated on dense rings, especially the role of self-gravity. The most important result has been the numerical prediction of small-scale wake structure in Saturns's rings (Nature 359, 619). We are investigating the observational implications of such wakes with photometric MC-simulation, and comparing the results to Voyager data, and to HST observations by Dick French. Other current interest is the apparantly irregular density variations in Saturn's B-ring: we are studying the properties of such extremely dense rings both with N-body simulations and with hydrodynamical stability analysis, in collaboration with Frank Spahns's group in Potsdam.

Our previous satellite resonance studies have dealt with the angular momentum exchange between rings and satellites, confirming numerically the validity of Goldreich-Tremaine predictions, and to some degree extending them to non-linear regime. Also, we have demonstrated the possibility of one-sided confinement of narrow ringlet in the 2:1 ILR of external satellite. Our recent studies have dealt with the azimuthally incomplete ring arcs of Neptune. We have shown (Science 282, 1102) that self-gravity of massive arc particles can stabilize them agains mutual impacts, and help to confine dust to the arc region in general. We are currently seaking for possible explanations for the recently observed shift between the locations of the arcs and the predictions of the Porco-Goldreich-Tremaine-model.

Our studies of interacting galaxies concentrate on the observed properties and N-body modelling of M51-type closely interacting galaxies. Observations include both visual and IR broad-band imaging, and Fabry-Perot velocity fields. Fairly detailed tidal models have been constructed for two systems, Arp 86 and the M51 itself. Our current interests concentrate on the innermost spiral structures, and the interplay between intrinsic spiral modes and externally induced tidal waves.

The other main application of our N-body modelling of galaxies have been the barred galaxies , especially the ring structures related to the resonances of the rotating bar. For example, a detailed N-body model has been developed for IC 4214, a prototypical weakly barred galaxy, using ring morphology and kinematics as diagnostics for the bar strength and pattern speed. Recent studies concentrate on the outer spiral modes, and their relation to the dominant bar mode: for example we address the non-linear mode coupling.

We are also studying the observed properties of bars in collaboration with Ron Buta, and their correlations with the gravitational perturbations associated with bars, derived from near IR-images.

Starting almost 20 years ago, various N-body methods have been developed in our group, first for planetary ring simulations and later also for galaxy studies. The main current methods include

  • Local simulations of planetary rings, including dissipative collisions and self-gravity.
  • Numerical codes for long-term integration of particle-satellite interactions, including radiative pressure.
  • 3D multi-grid code for simulation of interacting galaxies, composed of self-consistent disk+bulge+halo systems with both stars and gas.

Last updated: 22.2.2012