A multi-instrument study of Comet C/2009 P1 (Garradd) at 2.1 AU (pre-perihelion) from the Sun

We observed Comet C/2009 P1 (Garradd) on UT 2011 September 8th and 9th at a large heliocentric distance of 2.1 AU upon its entry to the inner Solar System. The observations were performed using high-resolution infrared spectrometers (NIRSPEC at Keck II and CSHELL at IRTF), allowing us to obtain strong detections of H2O, CO, CH4 and HCN and sensitive upper-limits for C2H6, C2H2, NH3 and HC3N. We oriented the slit at 45° from the projected Sun–comet vector and obtained spatial profiles of H2O, CH4, and HCN that revealed notable differences among these species. In particular, we observed a strong excess of water in the projected sunward direction, probably due to a solar-activated jet releasing water-rich icy grains.