Dynamical and Photometric Modeling of Saturn's Rings
(Dr. Heikki Salo, Division of Astronomy, Department of Physical Sciences, University of Oulu, Finland)

Our planetary ring studies concentrate on dense rings - the main A and B rings of Saturn - and especially on the role of ring particles' mutual self-gravity besides their physical impacts. The most important result has been the numerical prediction of small-scale wake structure in Saturns's rings (Salo 1992, Nature 359, 619). We are investigating the observational implications of such wakes with photometric Monte Carlo -simulations, and compare the results to Voyager data, to HST observations (PI R. G. French) and to Arecibo radar data (PI P. Nicholson). Gravity wakes are also marginally resolvable in recent Cassini images. 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 Potsdam group (J. Schmidt, F. Spahn).

RESEARCH TOPICS:

Dynamics of planetary rings:

• Gravitational wakes in Saturn's rings
• Gravitational aggregates in Saturn's outer A ring
• Viscous stability of dense planetary rings - Irregular structure of Saturn's B ring
• Ring-satellite interaction

Photometry of Saturn's rings:

• Photometric Monte Carlo modeling of dynamical simulation data
• Saturn A-ring azimuthal brightness asymmetry and gravitational wakes:
  modeling of Voyager, Hubble Space Telescope and Arecibo radar data
• General photometry of Saturn's rings: tilt and opposition effect

COLLABORATION:

• Photometric modeling: R.G. French, C. McGhee (Wellesley C.), L. Dones (U. Boulder), P. Nicholson (U. Cornell)
• Dynamics: J.Schmidt, F. Spahn (U. Potsdam)

RECENT PUBLICATIONS:

• Salo, H., Schmidt. J. & Spahn, F. (2001) : Viscous overstability in Saturn's B-ring: I. Direct simulations and measurement of transport coefficients. Icarus 153, 295-315.
• Schmidt. J., Salo, H., Spahn, F. & Petzschmann, O. (2001) : Viscous overstability in Saturn's B-ring: II. Hydrodynamic theory and comparison to simulations. Icarus 153, 316-331.
• Schmidt, J, Salo, H. (2003) : A weakly nonlinear model for oscillatory instability in Saturn's dense rings. Phys. Rev. Lett 90, 061102-1 - 061102-4
• Salo, H, Karjalainen, R (2003): Photometric modeling of Saturn's rings: I. Monte Carlo method and the effect of non-zero volume filling factor. Icarus 164, 428-460.
• Morishima, R, Salo, H (2004): Spin rates of small moonlets embedded in planetary rings: I. Three body calculations. Icarus 167, 330-346
• Salo, H, Karjalainen, R., French, R.G (2004): Photometric modeling of Saturn's rings: II. Azimuthal asymmetry in reflected and transmitted ligth. Icarus 170, 70-90.
• Karjalainen, R., Salo, H (2004): Gravitational accretion of patricles in Saturn's rings. Icarus in press.

Gravitational aggregates in Saturn's outer A ring

Viscous stability of dense planetary rings - Irregular structure of Saturn's B ring

Ring-satellite interaction

Photometric Monte Carlo modeling of dynamical simulation data

Saturn A-ring azimuthal brightness asymmetry and gravitational wakes:
modeling of Voyager, Hubble Space Telescope and Arecibo radar data

General photometry of Saturn's rings: tilt and opposition effect

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.