Development of SwRI's Comet Modeling Capabilities, 15-R9879

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Principal Investigator
Daniel C. Boice

Inclusive Dates:  09/01/08 – Current

Background - Comets are thought to hold important clues to the formation of our solar system; however, a complete picture of where and when comets formed doesn't exist. High resolution spectra of comets provide unique opportunities to advance our knowledge of parent molecules in comets, especially organics, and to identify important physico-chemical processes that occur in their atmospheres. SwRI proposes to analyze two unique observational datasets of comets Machholz and Tempel 1 using a state-of-the-art comet model, coupling time-dependent molecular fluorescence, gas dynamics and chemical kinetics. This is an important step because many aspects of comets can only be reliably analyzed using a sophisticated physico-chemical model with radiation coupling. This should result in an innovative and unique opportunity to advance our knowledge of the composition and physical properties of these small solar system bodies and their surrounding environments, thereby gaining clues to understanding the origins of the solar system and the origins of life on Earth.

Approach - No single computer code currently exists that is capable of addressing the key physical processes and conditions that are thought to be relevant to comets in a self-consistent manner. The primary goal of this project is to develop a general-purpose simulation for addressing physical and chemical processes in comets to advance our understanding of the cometary environment. The resulting modeling tool will couple gas dynamics, chemical kinetics, and time-dependent molecular fluorescence, and will be used to analyze two unique cometary datasets as a proof of concept. Researchers will then attack a range of open questions about comets and other small icy bodies via externally funded projects from NASA and NSF and support current and future space missions to comets, including new application areas for SwRI with strong relevance to SwRI's long-range plans for program development. This innovative, state-of-the-art model will enhance and combine the existing suite of comet codes at SwRI.

Accomplishments - Several technical advances in the development and coupling of existing comet codes have been accomplished to date. These include a more realistic transition from fluid dynamics to free molecular flow, extending the optical depth calculation to two dimensions and coupling to the molecular fluorescence code. SwRI has begun implementing automatic differentiation software to verify and validate the combined code using a multifaceted approach. With collaborators Prof. H. Kawakita and H. Kobayashi (Kyoto Sangyo University), SwRI has completed an analysis of comet Machholz spectra with respect to HCN and "hot" water bands, deriving mixing ratios for common molecules and their span through the surrounding region. SwRI also participated in the analysis of similar high-resolution spectra for the recent comet Lulin. After adapting the chemical and fluorescence models to comet Machholz for comparison, SwRI researchers completed the analysis of high-resolution spectral observations of HCN in the inner coma. Researchers have begun adapting the model to comet Tempel 1 for analysis of observations of the Deep Impact Mission (NASA) event with collaborators Profs. W. Jackson (UC Davis) and A. Cochran (UT Austin).

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