2004 Annual Science Report
NASA Goddard Space Flight Center Reporting | JUL 2003 – JUN 2004
Investigation of Parent Volatiles in Comets at Near Infrared Wavelengths
Cometary Research: Our group (DiSanti, Dello Russo, and Mumma) conducts studies of parent volatiles in comets through ground-based high-resolution spectroscopy at near-infrared (IR) wavelengths (~ 1—5 µm). This has been an exciting year with the availability of 2P/Encke (a short-period comet and member of Jupiter’s dynamical family) in Fall, 2003, and of two long-period (Oort cloud) comets (C/2001 Q4 NEAT and C/2002 T7 LINEAR) in Spring, 2004. Our observations of Encke permitted the volatile chemistry of a Jupiter Family comet to be characterized in unprecedented detail. Our studies of Q4 and T7 exploited their large geocentric Doppler shifts to conduct detailed studies of emissions that are normally obscured by atmospheric extinction, in particular transitions of CH4 and, to a lesser extent, CO. Our research emphasizes the volatile carbon-oxygen chemistry, in particular the efficiency of converting CO to formaldehyde and methyl alcohol on the surfaces of icy grain mantles prior to their incorporation into the nucleus. This process is expected to be temperature-dependent, and comet T7 in particular displayed very strong signatures of both H2CO and CH3OH, yet relatively weak CO, suggesting high conversion efficiency. Such measurements are important for establishing the role of comets in replenishing Earth’s oceans and for delivery of the seed organic molecules from which life emerged. Along with HCN and NH3 (both of which we also study), H2CO is thought to play a particularly significant role in the latter process.