DSMC Simulations of Irregular Source Geometries
for Io’s Pele Plume
William McDonielDavid Goldstein, Philip Varghese, Laurence Trafton
The University of Texas at Austin
42nd DPS Meeting October 6th, 2010
Supported by the NASA Planetary Atmospheres Program
Pele
Canopy rises to over 300kmDeposition ring is ~1200km acrossTemperatures in excess of 1000K observed via IRRing changes over time, but remains ovoid
10km
120km
Source Geometries•Previous plume simulations used only round vents.
•Irregularities in Pele’s structure likely caused by unsteadiness or source geometry.
•Steady irregularities due to source geometry, and this must be simulated
Observational clues to the actual source:
-consistently ovoid ring-black “butterfly wings”-Galileo IR image of part of Pele’s caldera-Galileo/Voyager images of the caldera
Basic DSMC Overview
• Simulates gas dynamics using a “large” number of representative particles
• Particle collisions and movement are de-coupled in a given timestep
• Binary collisions between particles in the same cell
• Particles move using F=ma
Plume Simulations
Earlier axisymmetric simulations of Pele using DSMC.The plume expands, collapses back on itself, and forms a large canopy.The gas can bounce off of the surface, and form secondary rings, depending on surface temperature.
Cold Line Source
Vent number density: 5 × 1018m-3 (under-resolved)
240km
1200km
10km
Hot Line Source
Focusing at hot conditions – 650K and 900m/s at the vent. Near-field number density contours at ground level and along the dashed line.
Focusing is more pronounced than with cold cases. Four orders of magnitude difference between red jets and blue expansion regions.13km
20kmA A’
A’
A
Cold Lava Lake
Vent number density: ~2 × 1016m-3.Orientation is almost exact.
120km
240km
1200km
Cold Lava Lake
A’
A
A
A’
B B’
B B’
Number density contours through the plume along two planes.240km
240km
Other Sources?
Conclusions•DSMC can provide insight into the source geometry of Ionian plumes.
•A curved line source, as seen in the Galileo IR image, can produce the features seen in observations of Pele’s deposition pattern.
•But the observed hot line cannot be the only source of plume material because it produces a ring with a different orientation.
•Gas must be produced elsewhere in the caldera, perhaps in a line across the top of the lava lake.
