The chemical composition of CO-rich comet C/2009 P1 (Garradd) at Rh = 2.4 and 2.0 AU before perihelion

TL;DR

This study quantified ten parent volatiles in comet C/2009 P1 (Garradd) at two distances before perihelion, revealing it to be a CO-rich comet with asymmetric outgassing and diverse active vents.

Contribution

First detailed infrared spectroscopic analysis of multiple volatiles in comet Garradd at different heliocentric distances, highlighting its CO-rich nature and complex outgassing behavior.

Findings

Comet Garradd is CO-rich with 12.51% abundance relative to water.

Detected asymmetric outgassing and different active vents for H2O and CO.

Identified the need for additional water to match typical organic abundance ratios.

Abstract

We quantified ten parent volatiles in comet C/2009 P1 (Garradd) before perihelion, through high-dispersion infrared spectra acquired with CRIRES at ESO's VLT on UT 2011 August 07 (Rh = 2.4 AU) and September 17-21 (Rh = 2.0 AU). On August 07, water was searched but not detected at an upper limit (3{\sigma}) of 2.1 \times 10^28 s-1, while ethane was detected with a production rate of 6.1 \times 10^26 s-1 (apparent mixing ratio > 2.90%). On September 17-21, the mean production rate for water was 8.4 \times 10^28 s-1, and abundance ratios (relative to water) of detected trace species were: CO (12.51%), CH3OH (3.90%), CH4 (1.24%), C2H6 (1.01%) and HCN (0.36%). Upper limits (3{\sigma}) to abundances for four minor species were: NH3 (1.55%), C2H2 (0.13%), HDO (0.89%) and OCS (0.20%). Given the relatively large heliocentric distance, we explored the effect of water not being fully sublimated within our FOV and identified the 'missing' water fraction needed to reconcile the retrieved abundance ratios with the mean values found for "organics-normal". 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 different active vents and/or the possible existence of polar and apolar ice aggregates in the nucleus. The high fractional abundance of CO identifies comet C/2009 P1 as a CO-rich comet.