Modeling Impacts on Icy Bodies: Applications to Saturn’s Moons Vanessa Lauburg TERPS Conference: December 7, 2004 Tethys Mimas Rhea

Motivation Solar System Formation Formation of moons around gas giants Key: understand internal structures of satellites Proposed Method: analyze global damage from large impacts

Goals of this Study Relating Global Damage to Internal Structure Simulate impacts on model satellites Vary internal structure: core size and density Measure damage: surface fragmentation, antipodal disruption Correlation between structure and damage? Simulate impacts on Saturn’s moons Rhea, Mimas, & Tethys Which internal structure values best reproduce observed damage?

Simulations Code 3D Smooth Particle Hydrodynamics triaxial objects, fragmentation Model Objects targets: silicate cores, water ice mantles impactors: undifferentiated water ice spheres Analysis peak surface velocity  seismic disturbances and terrain degradation peak tensile strength  surface rupturing

Results Fig. 1. Time Sequence: P wave passing through Tethys (basalt core), from t = 25 sec to t=300 sec (each frame advances 25 sec).

Results Seismic Energy Weakly Focused at Antipode correlation: core radius and terrain damage observed antipodal damage  core geometry? Tethys Simulations Produce Greatest Damage higher peak surface velocity and tensile stress than on Mimas or Rhea Expected! Tethys has the largest crater

Results Fig. 2. 2D projections of surfaces of (a) test satellite, (b) Mimas, (c) Rhea, and (d) Tethys. Color scale: peak surface velocity.

Conclusions 3D simulations show weak antipodal focusing strong focusing in previous 2D sims is due to axisymmetry of the code Core radius is correlated with antipodal damage core density not as important observations of terrain damage might provide info about core geometry Future Work fragmentation results are inconclusive (inadequate resolution) improve resolution, laboratory constraints on properties of ice

References Bruesch, L.S., Asphaug, E., Modeling global impact effects on middle-sized icy bodies: applications to Saturn’s moons. Icarus 168, De Pater, I., Lissauer, J., Planetary Sciences. Cambridge University Press, Cambridge, UK.

Extra Bits Tethys (Odysseus) : D/D T = 0.38 Mimas (Herschel) : D/D M = 0.34 Rhea (Tirawa) : D/D R = 0.23 Density of impactor: