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 descriptionIndividual 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 modelH, 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

Density

Electron temperature

Magnetic field

Plasma velocities

Plasma temperatures

Den

sity

Lore

ntz-

forc

e

Magnetic field

Tem

pera

ture

s

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)