Theoretical Models in support of RPWI

1
Theoretical Modelsin support of RPWI
Io
Ganymede
Europa

• I. Mueller-Wodarg
• Imperial College London

2
Plasma environment
Europa Ganymede Callisto
Bo (nT) 370-460 64-113 4-42
Ne (cm-3) 18-250 1-10 0.01-0.70
Ti (eV) 50-400 10-100 10-100
Te (eV) 100 300 500
Orbital vel (km/s) 14 11 8
Plasma vel (km/s) 70-100 95-163 130-280
Alfvén speed (km/s) 145-700 130-1700 230-4400
Ped conductance (S) 30 2 1000
Plasma freq e- (kHz) 38-140 9-28 0.9-7.5
Plasma freq ions (Hz) 260-4300 150-4200 15-7300
Ion gyroradius (km) 8-12 36-13 530-34
Pickup ion gyro-r (km) 19-15 200-110 4200-400
3
Atmospheres of Galilean Moons

• Formation Sputtering
• Surface sputtering by magnetospheric ions
  (primary)
• Sputtering by ionospheric pickup ions
  accelerated by corotation electric field
  (secondary)
• Loss
• Thermal escape (Jeans escape)
• Ionization, pickup
• Atmospheric sputtering trajectories outside
  exobase

4
Atmosphere properties
Europa Ganymede Callisto

O2 (cm-2) 2.4-14 x 1014 (1-10) x 1014 3 x 1016 (?)
O (cm-2) lt 1013 (?) lt 1013
CO2 (cm-2) (?) (?) 8 x 1014
Na (cm-2) 4 x 109 (5 RE) lt 108 (3-6 RG) (?)
H (cm-2) (?) 2.4 x 1012 (?)
Ionosphere 104 cm-3 (need illumination of trailing hemisph) 102 cm-3 2 x 104 cm-3

• Atmospheres ionospheres highly variable
• Self-regulation enhanced neutral densities lead
  to larger ionosphere densities, hence stronger
  currents reduced ionospheric E-field increases
  shielding reduces sputtering

5
Europa
Kliore et al. (1997)
6
Ganymede
Eviatar et al. (2001)
7
Callisto
Kliore et al. (2002)
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Approaches for simulating plasma environment and
atmospheres

• Analytical solutions not possible
• Atmospheres Monte Carlo codes
• Plasma magnetic environment MHD and Hybrid
  models
• Atmosphere-magnetosphere interaction Monte Carlo
  model combined with fixed B field

9
Moon atmosphere models

• Europa
• Ip (1996) Europa O2 exosphere model
• Saur et al. (1998) neutral atmosphere and plasma
  interaction model for Europa
• Kabin et al. (1999)
• Liu et al. (2000)
• Shematovich and Johnson (2001) 1D Monte Carlo
  Europa oxygen model
• Smyth and Marconi (2006) (2D Monte Carlo model)

10
Moon atmosphere models

• Callisto
• Liang et al. (2005)
• Ganymede
• Yung and McElroy (1977)
• Purves and Pilcher (1980)
• Wong et al. (1999) (2D)
• Marconi (2007) (Multi-species, 2D)

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Atmosphere-Magnetosphere Models

• Ganymede
• Stone and Armstrong (2001) (MHD)
• Kopp and Ip (2002) (MHD)
• Paty and Winglee (2004) (Multi-fluid)
• Europa
• Saur et al. (1998)
• Kabin et al. (1999)
• Liu et al. (2000)
• Zimmer et al. (2000)
• Schilling et al. (2007)

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Other models

• Mercury magnetosphere hybrid model (Trávnícek et
  al., 2009)
• Enceladus, Titan?

13
Needs for RPWI

• Engineering models for moon neutral atmosphere
  and ionosphere densities
• Average B field engineering model describing
  vicinity of Galilean moons
• E field model
• Software for interfacing simulated RPWI with
  atmosphere plasma environment models
• Any more?