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Project Progress

The goal of this task is to determine the chemical composition of icy bodies and establish their potential for delivering pre-biotic organic materials and water to the young Earth and other planets. This is being performed through detailed chemical modeling, coupled with physical evolution, of the protosolar nebula. Related observational, theoretical, and laboratory studies are also being undertaken.

We have made significant progress in several theoretical and observational subprojects. These are aimed at understanding the relative contributions of interstellar and nebular chemistries to cometary composition. Two book review chapters have been completed. These summarize the important physical and chemical processes occurring in protoplanetary disks, such as the early protosolar nebula. Theoretical models of disk chemistry are described and the connection between these processes and the composition of primitive solar system materials is made (Markwick & Charnley 2004; Ciesla & Charnley 2005). Using a variant of the UMIST disk chemistry code, we have made preliminary studies of gas-grain deuterium fractionation processes in the comet-forming regions of model disks. We have included a full deuterium chemistry into our disk chemistry model, including multiple deuteration driven by H₂D, HD₂ and D₃⁺ reactions. A paper has been submitted for publication (Markwick & Charnley 2005). This work complements the direct searches for deuterated cometary molecules we are also undertaking (see below).

We have published more of our Submillimeter Array mapping data on organic molecules in the ‘hot corinos’ of the low-mass IRAS 16293-2422 binary system (Huang et al. 2005). Our new H¹³CN interferometric data clearly shows Keplerian rotation in subsource A, and hence the presence of a protostellar accretion disk. A VLA proposal has been submitted with NAI —GCA collaborators L. Mundy and J. Pedelty to perform high-resolution observations of this source at cm wavelengths. We performed a series of radio observations of comets C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR) using the JCMT and the ARO 12m and SMT telescopes. We were able to detect deuterated formaldehyde in C/2002 T7. This is the first time this molecule has been detected in a comet. The inferred D/H ratio is large, consistent with formation in a very cold environment, and a paper is being prepared for submission to Nature. We also observed hydrogen cyanide emission in C/2001 Q4, in collaboration with optical observers who have determined the C¹⁵N/C¹⁴N ratio. However, we were only able to able to determine upper limits to the important HC¹⁵N/HC¹⁴N ratios; a paper is being prepared for submission.

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