Energetic Particle Impacts in Saturns Magnetic Field:

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Energetic Particle Impacts in Saturns Magnetic
Field

• Simulating Charged Particle Motion to Explain
  Satellite Surface Features
• Rob Zellem and Geraint Jones (University College
  London)

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Tethys Images

• Images of Tethys by Cassini and Voyager revealed
  many puzzling surface features
• Equatorial areas of differing surface brightness

Stooke 2002
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Tethys Images
http//www.planetary.org/blog/article/00001813/
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Other Studies

• Similar features have been detected on Jupiters
  Galilean moons
• Studies have been conducted to determine if these
  surface features are due to energetic charged
  particle impacts
• Cooper et al. 2001, Pospieszalska Johnson 1989
• Simulated particle collisions with the moons
• Determined that their results satisfactorily
  explained such brightness features
• Interestingly, such a study has yet to be
  conducted in the Saturnian system

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The Goal

• To build our own simulation software to determine
  if the brightness features on Tethys are caused
  by the impact by highly energetic charged
  particles
• Aided by data from Cassinis Magnetosphere
  Imaging Instrument (MIMI), which observes the
  energetic charged particle population trapped in
  Saturns magnetosphere
• Allow a realistic representation of the moons
  environments and increase the simulations
  efficiency
• Simulator outputs collision position, allowing
  the construction of a surface collision map
• Compared to the Voyager and Cassini images to
  determine which particle population has caused
  the moons brightness variations

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Motions of Charged Particles in a Planetary
Magnetic Field

• Helical Motion

?
Bz
v

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Motions of Charged Particles in a Planetary
Magnetic Field

• Sine and cosine equations
• Gyroradius
• Gyroperiod

Parks 2004
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Motions of Charged Particles in a Planetary
Magnetic Field
http//www-ssg.sr.unh.edu/tof/Smart/Students/lees/
periods.html
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Change previous image to include Saturn, flipping
B-field, and add a moon

• Might also want to include a slide of physical
  properties and make sure to say that Tethys
  orbit is synchronous

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Bounce and Drift Motion
Parks 2004
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Parmot Particle Motion Simulator

North celestial pole
10rmoon
B
Saturn
(0, 0, 0)
Direction of moon orbital motion

























10rmoon

10rmoon
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Parmot input from MIMI
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Parmot Particle Motion Simulator
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Output

• Electrons - overall, there were 16,316 collisions
• Simulation time
• Electrons 7 hours
• Protons 4 hours
• Singly-ionized oxygen 4 hours

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(No Transcript)
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Proton Plot
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Electron Plot
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Singly-ionized Oxygen Plot
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Initial Conclusions

• Appears Tethys surface features are due to
• Lack of collisions by electrons
• Collisions by singly-ionized oxygen
• Particle efficiency
• Oxygen impacts likely more efficient than
  electron impacts due to larger mass
• Appears, at this stage, that singly-ionized
  oxygen is the cause of Tethys albedo

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Future Tasks

• Magnetic field
• Existence of magnetic field gradient
• Assumed that the B-field inside the simulation
  box is constant as simulation box size is much
  smaller than the overall magnetic field line
  length
• Needed as it causes particle drift
• Magnetic field x-y plane is slightly above
  Tethys equator
• Both limited by available simulation time
• Preliminary runs of Parmot with a more realistic
  magnetic field have indicated that they will take
  longer than a few days
• Run Parmot on multiple computers
• Trying to port Parmot to run on three computers
  (one for each particle type) in the lab for a few
  days

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Thank you

• Any questions?