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

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 $Q_{CO}=(1.6\pm 0.5)\times 10^{27}$ 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.

8 pages, 3 figures, accepted to be published in ApJ Letters

References in corpus (4)

• CO in distantly active comets
• A Comet Active Beyond the Crystallization Zone
• Cometary Activity Begins at Kuiper Belt Distances: Evidence from C/2017 K2
• Prediscovery Observations and Orbit of Comet C/2017 K2 (PANSTARRS)

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