Ground-based Multiwavelength Observations of Comet 103P/Hartley 2

TL;DR

This study presents multiwavelength radio to submillimeter observations of comet 103P/Hartley 2, revealing molecular compositions, production rates, and isotopic ratios that inform understanding of cometary chemistry and activity near perihelion.

Contribution

It provides the first comprehensive multiwavelength dataset of 103P/Hartley 2's molecular emissions during its perihelion passage, including water production and isotopic ratios, supporting the NASA EPOXI mission.

Findings

Detected HCN, H2CO, CS, and OH in the comet.

Measured water production rate between 0.67 and 1.07 x 10^28 s^-1.

Derived an ortho:para H2CO ratio indicating a spin temperature >8 K.

Abstract

The Jupiter-family comet 103P/Hartley 2 (103P) was the target of the NASA EPOXI mission. In support of this mission, we conducted observations from radio to submillimeter wavelengths of comet 103P in the three weeks preceding the spacecraft rendezvous on UT 2010 November 4.58. This time period included the passage at perihelion and the closest approach of the comet to the Earth. Here we report detections of HCN, H2CO, CS, and OH and upper limits for HNC and DCN towards 103P, using the Arizona Radio Observatory Kitt Peak 12m telescope (ARO 12m) and submillimeter telescope (SMT), the James Clerk Maxwell Telescope (JCMT) and the Greenbank Telescope (GBT). The water production rate, QH2O = (0.67 - 1.07) x 10^28 s^-1, was determined from the GBT OH data. From the average abundance ratios of HCN and H2CO relative to water (0.13 +/- 0.03 % and 0.14 +/- 0.03 %, respectively), we conclude that H2CO is depleted and HCN is normal with respect to typically-observed cometary mixing ratios. However, the abundance ratio of HCN with water shows a large diversity with time. Using the JCMT data we measured an upper limit for the DCN/HCN ratio <0.01. Consecutive observations of ortho- H2CO and para-H2CO on November 2 (from data obtained at the JCMT), allowed us to derive an ortho : para ratio (OPR) ~ 2.12 +/- 0.59 (1sigma), corresponding to Tspin > 8 K (2sigma).