Computer Science
Scientific paper
Oct 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011epsc.conf..260r&link_type=abstract
EPSC-DPS Joint Meeting 2011, held 2-7 October 2011 in Nantes, France. http://meetings.copernicus.org/epsc-dps2011, p.260
Computer Science
Scientific paper
Our global model of the comet - solar wind interaction [7], originally developed by [4] for comet 1P/Halley, has been used to simulate the involved ion neutral chemistry for an in depth comparison with the measurements obtained by Giotto's Ion Mass Spectrometer [1]. The Block Adaptive Tree Solarwind Roe-type Upwind Scheme (BATSRUS) solves the governing equations of magnetohydrodynamics [8] accounting for photoionization, recombination, and ion-neutral frictional drag in an adaptive unstructured Cartesian mesh. Such an approach allows resolving the various features of the comet involving very different length scales. Here we focus on the plasma environment of comet 67P/Churyumov-Gerasimenko the target of the European Space Agency's Rosetta mission. After the rendezvous with the comet the Rosetta spacecraft will accompany 67P/Churyumov-Gerasimenko from almost 3.5 AU all the way to perihelion at 1.3 AU. [5] presented model predictions for the comet's plasma environment in the whole range of heliocentric distances relevant for Rosetta using our magnetohydrodynamics model BATSRUS. In their work the neutral gas production rate was approximated as spherically symmetric. Here we are also interested in the effect of asymmetric neutral gas distributions. Asymmetric neutral gas production rates will affect the ion-neutral drag force that is balanced by the magnetic pressure gradient force at the location of the cavity boundary. In particular at larger heliocentric distances, where the strength of the interplanetary magnetic field and the magnetic pressure gradient force decrease, the distribution of active regions over the comet's surface influences the shape of the magnetic cavity. This is especially interesting as the geometry of the cavity influences the topology of the plasma streamlines crossing the shock. The jump-conditions can be derived from integrating the magnetohydrodynamics equations across the shock and are called Rankine-Hugoniot equations for MHD. The tail-ward plasma flow can be significantly altered and then concentrated in the plane perpendicular to the Interplanetary Magnetic Field (IMF). This effect might be observable by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) and the Rosetta Plasma Consortium (RPC) instrument packages at specific locations around the comet. We will also show that, depending on the asymmetry of the neutral gas distribution and the strength of the magnetic field, the plasma flow around the cavity boundary can even become unstable due to the formation of Kelvin- Helmholtz instabilities.
Combi Michael R.
Daldorff K. S. L.
Gombosi Tamas I.
Hansen Kenneth Calvin
Rubin Mathieu
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