Cometary Activity Discovered on a Distant Centaur: A Nonaqueous Sublimation Mechanism

Centaurs are minor planets thought to have originated in the outer solar system region known as the Kuiper Belt. Active Centaurs enigmatically display comet-like features (e.g., tails, comae) even though they orbit in the gas giant region where it is too cold for water to readily sublimate. Only 18 active Centaurs have been identified since 1927 and, consequently, the underlying activity mechanism(s) have remained largely unknown up to this point. Here we report the discovery of activity emanating from Centaur 2014 OG392, based on archival images we uncovered plus our own new observational evidence acquired with the Dark Energy Camera (Cerro Tololo Inter-American Observatory Blanco 4 m telescope), the Inamori-Magellan Areal Camera & Spectrograph (Las Campanas Observatory 6.5 m Walter Baade Telescope), and the Large Monolithic Imager (Lowell Observatory 4.3 m Discovery Channel Telescope). We detect a coma as far as 400,000 km from 2014 OG392, and our novel analysis of sublimation processes and dynamical lifetime suggest carbon dioxide and/or ammonia are the most likely candidates for causing activity on this and other active Centaurs. We find 2014 OG392 is optically red, but CO2 and NH3 are spectrally neutral in this wavelength regime so the reddening agent is as yet unidentified.