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Comet 1P/Halley Multifluid MHD
model for the Giotto Fly-By
M. Rubin, M. R. Combi, L. K. S. Daldorff,
T. I. Gombosi, K. C. Hansen, Y. Shou, V.
M. Tenishev, G. Tóth, B. van der Holst,
and K. Altwegg
Rubin et al. 2014, ApJ, 781, 86
Model description
Individual ion fluids with their own continuity (mi), momentum (miuxi, miuyi, miuzi), and
pressure equations (pi)
- SWp+ (Origin: SW, only sinks inside the model)
- H2O+ (Origin: Photoionization of cometary neutrals)
- H+
(Origin: Photoionization of cometary neutrals)
- separate electron pressure equation (pe→Te)
Neutral gas (analytic description)
H2O is described by a Haser model
H, H2 is fitted to Combi (1996)
Included physics :
- Photoionization & dissociation, electron-impact ionization
- Ion-electron recombination
- Ion-neutral charge exchange (through friction term)
- Lorentz-force interaction between the fluids
- Elastic collision (ion-ion, ion-electron, ion-neutral, electron-neutral)
- Electron heating by photoelectrons
- H2O cooling of electrons (inelastic electron-H2O collisions)
- UV absorption by photoionization
Modeled species
Model input
Results
• Comparison with Giotto observations
• Overview of the different plasma species
Nucleon density [amu/cm ]
3
Density
5
106
10
2
3
104
10
10
0
101
10
10-1
10
2
10
3
4
10
6
JPA protons
BATS-R-US solar wind protons
BATS-R-US cometary light ions
JPA heavy ions
IMS HIS 12-32 amu ions
BATS-R-US cometary heavy ions
5
10
10
Distance to comet [km]
10
Electron temperature
Temperature [K]
106
105
104
103
102
101
10
2
10
3
4
10
6
Gombosi et al. (1996)
Eberhardt and Krankowsky (1995)
BATS-R-US
5
10
10
Distance to comet [km]
10
0
-400
200
400
600
Neubauer (1987)
BATS-R-US
Universal Time
Closest
Mar 14, 1986 Mar 14, 1986
Approach
00:08
00:13
0
Time from closest approach [s]
-200
1986 Mar 13, 1986
53
23:58
Magnetic field
Plasma velocities
Velocity [km/s]
1000
100
10
1
0.1
2
10
10
3
5
10
6
JPA protons
BATS-R-US solar wind protons
BATS-R-US cometary light ions
JPA heavy ions
IMS HIS Mass Analyzer 12-32 amu ions
IMS HIS Angle Analyzer 12-32 amu ions
IMS HERS 12-32 amu ions
BATS-R-US cometary heavy ions
4
10
10
Distance to comet [km]
10
Plasma temperatures
Temperature [K]
7
108
10
4
5
106
10
10
2
103
10
101
10
2
10
3
4
10
6
JPA protons
BATS-R-US solar wind protons
BATS-R-US cometary light ions
JPA water group
IMS HIS Mass analyzer water group
IMS HIS Angle analyzer water group
IMS HERS water group
BATS-R-US cometary heavy ions
5
10
10
Distance to comet [km]
10
Density
Lorentz-force
Magnetic field
Temperatures
Conclusions
• Multifluid MHD seems to be doing a reasonable
job in fitting Giotto plasma observations
• Co-located inner shock for cometary species
• Ion pile-up does not necessarily peak at the same
location for the different species
• Solar wind absent from the innermost region
• Lorentz-force interaction between the fluids can
be observed (non-vanishing Bx component)