The Chemical Composition of CO-Rich Comet C/2009 P1 (Garradd) at Rh = 2.4 and 2.0 AU Before Perihelion

We quantified 10 parent volatiles in comet C/2009 P1 (Garradd) before perihelion, through high-dispersion infrared spectra acquired with CRIRES at ESO’s Very Large Telescope on UT 2011 August 7 (Rh = 2.4 AU) and September 17–21 (Rh = 2.0 AU). On August 7, water was searched for but not detected at an upper limit (3σ) of 2.1 × 1028 s−1, while ethane was detected with a production rate of 6.1 × 1026 s−1. On September 17–21, the mean production rate for water was 8.4 × 1028 s−1, and five trace species (CO, C2H6, CH4, HCN, and CH, OH) were securely detected, and (3σ) upper limits were retrieved for NH3, C2H2, OCS, and HDO. Given the relatively large heliocentric distance, we explored the effect of water not being fully sublimated within our field of view and identified the “missing” water fraction needed to reconcile the retrieved abundance ratios with the mean values found for “organics-normal” comets. The individual spatial profiles of parent volatiles and the continuum displayed rather asymmetric outgassing. Indications of H2O and CO gas being released in different directions suggest chemically distinct active vents and/or the possible existence of polar and a polar ice aggregates in the nucleus. The high fractional abundance of CO identifies comet C/2009 P1 as a CO-rich comet.