The Organic Volatile Composition of Comet C/2004 Q2 (Machholz) in November, 2004 and in January, 2005: A Test for Internal Heterogeneity Within the Nucleus

We obtained quantitative measurements of parent volatiles in Comet C/2004 Q2 (Machholz), using NIRSPEC at Keck-2 on Mauna Kea, Hawaii. Emission was detected from multiple parent species, including H₂O, HCN, CH₄, C₂H₂, C₂H₆, CO, H₂CO, and CH₃OH. We will present spectra, rotational temperatures, absolute production rates, and relative abundances of organic molecules with respect to H₂O. Significantly, the comet was observed at two different heliocentric distances: near 1.49 AU on UT 28-29 November 2004, and near 1.21 AU on UT 19 January 2005. Comparison of the organic volatile composition measured at these two dates is a possible test for internal heterogeneity (or lack thereof) of the nucleus of C/2004 Q2 (Machholz). Results will be reported.

We gratefully acknowledge support from NASA's Planetary Astronomy Program to M.J.M. and M.A.D., NASA's Astrobiology Program to M.J.M., and from NSF's RUI Program to K.M.-S.