Discovery of Carbon Monoxide in Distant Comet C/2017 K2 (PANSTARRS)

TL;DR

This paper reports the first detection of gaseous carbon monoxide in the distant Oort cloud comet C/2017 K2, confirming supervolatile sublimation as a driver of activity at large heliocentric distances.

Contribution

It presents the first observational evidence of CO gas in C/2017 K2, supporting the hypothesis that supervolatile sublimation causes activity far from the Sun.

Findings

Detected CO in C/2017 K2 at 6.72 au heliocentric distance.

Measured CO production rate of approximately 1.6 x 10^27 s^-1.

Confirmed supervolatile sublimation as a key activity mechanism in this comet.

Abstract

Optical observations of the Oort cloud comet C/2017 K2 (PANSTARRS) show that its activity began at large heliocentric distances (up to 35 au), which cannot be explained by either the sublimation or the crystallization of water ice. Supervolatile sublimation, most likely of carbon monoxide (CO), has been proposed as a plausible driver of the observed mass loss. Here, we present the detection of the J = 2$-$1 rotational transition in outgassed CO from C/2017 K2 when at heliocentric distance $r_H$ = 6.72 au, using the James Clerk Maxwell Telescope. The CO line is blue-shifted by 0.20$\pm$0.03 km s$^{-1}$ with an area and width of 8.3$\pm$2.3 mK km s$^{-1}$ and $0.28\pm$0.08 km s$^{-1}$, respectively. The CO production rate is $Q_{CO} = (1.6\pm0.5) \times10^{27}$ s$^{-1}$. These are the first observations of a gaseous species in C/2017 K2 and provide observational confirmation of the role of supervolatile sublimation in this comet.