Dynamics of Cometary Environments

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

AST 0707283 Combi Most information about the composition and structure of comets as a group continues to come from model analyses of observations of gas and dust in their comae, or atmospheres. The study of all planetary atmospheres, including comets, has reached the stage where complex model simulations are required to understand and interpret their global distribution and dynamics. This comet-modeling program uniquely addresses the full range of cometary coma phenomena and physical regimes with state-of-the-art numerical simulation codes. Drs. Combi and Gombosi have the demonstrated experience in applying these codes directly to the analysis of observations. Continuing development of models benefits from the rapid expansion in capabilities of computers (speed, number of processors and memory) and high performance algorithms enabling multi-dimensional simulation techniques to be applied. The tightly integrated approach of this effort is unique and particularly powerful for the study of multiscale phenomena, from the scale of meters near the surface to tens of millions of km far from the nucleus. In comets various physical and chemical processes operate on highly disparate scales, therefore this methodology has particular significance for understanding the delicate interplay between a wide range of aeronomical, dusty gas dynamic and plasma-physical processes. The long term goal of this project is the development and application of a multiscale, self-consistent comprehensive modeling capability for neutrals and plasma in cometary atmospheres extending from the complex 3D nucleus to tens of millions of kilometers into the outer atomic coma and tail and the contaminated (by cometary pick-up ions) solar wind. The model will support analysis and interpretation of spectroscopic and morphological observations of cometary environments at all stages of its development. Specific scientific objectives for this funding period, which represent the intellectual merit, of the proposed research are: 1. To combine 3D dusty-gas kinetics and 3D magnetohydro-dynamic (MHD) models with a thermo-physical model description for the nucleus surface/coma boundary layer to make a unique modeling tool for understanding the entire range of observed cometary coma phenomena. 2. To apply multispecies (multiple continuity equations) MHD to comets and to perform a complete parameter study of the effects of time-variations of solar wind (IMF direction, plasma sheet crossings, etc.) on the ion tail, as well as using steady-state simulations for a parameter study of the overall global variation of the comet plasma environment with gas production rate, heliocentric distance and solar wind conditions. 3. To perform the first resistive Hall MHD calculations for comets. 4. To considerably expand and generalize the integrated capability to calculate detailed x-ray emissions in comets using our 3D MHD model as a basis. 5. To use the evolving new modeling tools for interpreting observations from a variety past comets as well as target-of-opportunity comets including ion and x-ray observations. Finally, the project has a significant broader impact in its educational component that will provide support in the training one graduate student, and additionally that the continued development of the physical and numerical methods in the models will benefit to other applications of the basic codes. This cross talk from one application to another has an established history of great benefit to all applications of the numerical codes. ***