Recurrent Activity from (248370) 2005 QN173: A Main Belt Comet

We present evidence that active asteroid (248370) 2005 QN₁₇₃ has displayed comet-like activity during at least two perihelion passages. This finding, together with activity more recently discovered by other researchers, demonstrates (248370) 2005 QN₁₇₃ has been recurrently active near perihelion, a key diagnostic indicator that tells us that the observed activity is most likely sublimation driven. This evidence further suggests (248370) 2005 QN₁₇₃ is likely to be a member of the Main Belt Comets, a subset of active asteroids that orbit entirely within the Main Asteroid Belt and that display activity that is thought to be driven by sublimation.

Activity caused by sublimation holds clues about the current solar system distribution of volatiles, plus can provide insight into the origins of the water on Earth. Yet active asteroids – objects with an asteroid orbit but with comet-like features such as a tail or coma – are rare, with fewer than 30 of these bodies found to date. The rarity of these objects is due in large part to the observational challenges of detecting their typically faint coma. We set out to locate publicly available archival astronomical image data of (248370) 2005 QN₁₇₃ which could help us characterize the object. Making use of our own custom pipeline created as part of our Citizen Science project “Active Asteroids” we found roughly 50 images with sufficient quality and depth to definitively identify (248370) 2005 QN₁₇₃. From these we were able to produce 15 co-added images, 10 of which proved sufficient for detecting activity. Of these only one image clearly showed activity, an image taken 22 July 2016 with the Dark Energy Camera on the Blanco 4 m telescope at the Cerro Tololo Inter-American Observatory in Chile.

(248370) 2005 QN₁₇₃ is nearing the end of its apparition in late 2021, and when it is again observable (late 2022) it will be beyond 3 au from the Sun. Our analysis suggests (248370) 2005 QN₁₇₃ is most likely to be active interior to 2.7 au, thus we urge the community to observe this object while it is yet active.

This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under grant No. 2018258765. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. Funded in part by NASA grant No. 80NSSC19K0869 and NASA grant No. 80NSSC21K0114.