Tentative detection of cyclopropenylidene in comets

ABSTRACT We report the tentative detection of the ring molecule cyclopropenylidene (c-C$_3$H$_2$) in cometary comae. We observed three short-period comets: 73P/Schwassmann–Wachmann 3, 17P/Holmes, 103P Hartley 2, and two Oort Cloud comets: C/2007 N3 (Lulin) and C/2012 F6 (Lemmon) with the Arizona Radio Observatory Submillimeter Telescope (SMT) and the Atacama Large Millimeter/submillimeter Array (ALMA). We tentatively detected c-C$_3$H$_2$ in three of the comets, with molecule production rates in the range of $(0.2\!-\!3.8)\times 10^{25}$ molecules s$^{-1}$, and c-C$_3$H$_2$/H$_2$O mixing ratios of 0.01–0.19 per cent. Evidence from both the single-dish and interferometric data points to the presence of c-C$_3$H$_2$ being of a discrete transient nature and exhibiting an extended spatial distribution, indicating production from the decomposition of organic dust particles in the coma.