nai

Project Progress

Comet 2P/Encke . M. Mumma, M. DiSanti, N. Dello Russo, B. Bonev, K. Magee-Sauer, and E. Gibb investigated the composition of comet 2P/Encke at infrared wavelengths. Six nights of observing time was awarded at the NASA Infrared Telescope Facility and the W.M. Keck Observatory in November, 2003, for this Jupiter-family comet of probable Kuiper-belt origin. Long-slit spectra from the facility instruments CSHELL (Infrared Telescope Facility (IRTF)) and NIRSPEC (Keck) featured both high spectral dispersion and high spatial resolution about the nucleus. H₂O, C₂H₆ , CH₃ OH, HCN, and C₂H₂ were detected (the symmetric hydrocarbons for the first time in Encke), and production rates and rotational temperatures were determined. Rotational analysis of H₂O and C₂H₆ suggested very cold rotational distributions for coma gases (T rot ~ 20 — 30K). Relative abundances for C₂H₆ , CH₃OH, HCN, and C₂H₂ with respect to water were close to those typically seen in Oort cloud comets, while the abundance of hypervolatile CH 4 was severely depleted. This represents the most detailed study of a comet of probable Kuiper-belt origin with high-resolution ground-based infrared spectroscopy, and serves as a model for future studies of faint comets.