Uncorrelated Volatile Behavior During the 2011 Apparition of Comet C/2009 P1 Garradd

The High Resolution Instrument Infrared Spectrometer (HRI-IR) on board the Deep Impact Flyby spacecraft detected H 2 O, CO 2 , and CO in the coma of the dynamically young Oort Cloud comet C/2009 P1 (Garradd) post-perihelion at a heliocentric distance of 2 AU. Production rates were derived for the parent volatiles, Q H2O = 4.6 ± 0.8 × 10 28 , Q CO2 = 3.9 ± 0.7 × 10 27 , and Q CO = 2.9 ± 0.8 × 10 28 molecules s −1 , and are consistent with the trends seen by other observers and within the error bars of measurements acquired during a similar time period. When compiled with other observations of Garradd's dominant volatiles, unexpected behavior was seen in the release of CO. Garradd's H 2 O outgassing, increasing and peaking pre-perihelion and then steadily decreasing, is more typical than that of CO, which monotonically increased throughout the entire apparition. Due to the temporal asymmetry in volatile release, Garradd exhibited the highest CO to H 2 O abundance ratio ever observed for any comet inside the water snow line at ∼60% during the HRI-IR observations. Also, the HRI-IR made the only direct measurement of CO 2 , giving a typical cometary abundance ratio of CO 2 to H 2 O of 8% but, with only one measurement, no sense of how it varied with orbital position.