A Dormant Captured Oort Cloud Comet Awakens: (18916) 2000 OG44

Abstract

We report the discovery of activity emanating from (18916) 2000 OG44 (alternately designated 1977 SD), a minor planet previously reported to be both an extinct comet and an asteroid on a cometary orbit. We observed 2000 OG44 with a thin tail oriented towards the coincident antisolar and antimotion vectors (as projected on the sky) in images we acquired on UT 2023 July 24 and 26 with the Apache Point Observatory 3.5 m Astrophysical Research Consortium telescope (New Mexico, USA). We also include observations made in Arizona with the Vatican Advanced Technology Telescope at the Mount Graham International Observatory and the Lowell Observatory Lowell Discovery Telescope near Happy Jack. We performed dynamical simulations that reveal 2000 OG44 most likely originated in the Oort cloud, arriving within the last 4 Myr. We find 2000 OG44, which crosses the orbits of both Jupiter and Mars, is at present on an orbit consistent with a Jupiter-family comet. We carried out thermodynamical modeling that informed our broader diagnosis that the observed activity is most likely due to volatile sublimation.