Transcript Modeling Impacts on Icy Bodies: Vanessa Lauburg Applications to Saturn’s Moons

Modeling Impacts on Icy Bodies:
Applications to Saturn’s Moons
Rhea
Tethys
Mimas
Vanessa Lauburg
TERPS Conference: December 7, 2004
Motivation
Solar System Formation
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Formation of moons around gas giants
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Key: understand internal structures of satellites
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Proposed Method: analyze global damage
from large impacts
Goals of this Study
Relating Global Damage to Internal Structure
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Simulate impacts on model satellites
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Vary internal structure: core size and density
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Measure damage: surface fragmentation, antipodal
disruption
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Correlation between structure and damage?
Simulate impacts on Saturn’s moons Rhea, Mimas, & Tethys
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Which internal structure values best reproduce observed
damage?
Simulations
Code
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3D Smooth Particle Hydrodynamics
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triaxial objects, fragmentation
Model Objects
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targets: silicate cores, water ice mantles
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impactors: undifferentiated water ice spheres
Analysis
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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
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correlation: core radius and terrain damage
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observed antipodal damage  core geometry?
Tethys Simulations Produce Greatest Damage
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higher peak surface velocity and tensile stress than
on Mimas or Rhea
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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
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strong focusing in previous 2D sims is due to
axisymmetry of the code
Core radius is correlated with antipodal damage
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core density not as important
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observations of terrain damage might provide info
about core geometry
Future Work
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fragmentation results are inconclusive (inadequate resolution)
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improve resolution, laboratory constraints on properties of ice
References
Bruesch, L.S., Asphaug, E., 2004. Modeling global impact effects on
middle-sized icy bodies: applications to Saturn’s moons. Icarus
168, 457-466
De Pater, I., Lissauer, J., 2001. Planetary Sciences. Cambridge
University Press, Cambridge, UK.
Extra Bits
Tethys (Odysseus) : D/DT = 0.38
Mimas (Herschel) : D/DM = 0.34
Rhea (Tirawa) : D/DR = 0.23
Density of impactor: 2-3.97