RESTing Comets: Studying Dormant Comets via a Remnant Emission Survey Tool

Past studies have explored the ambiguous boundary between asteroids and dormant comets, emphasizing the subtle differences that make it difficult to distinguish them [1-3]. Within asteroid populations, for example, some bodies have exhibited signs of transient activity, which challenges the common definition of asteroids being inactive bodies, and suggests that at least some may be of cometary origin. Dormant comets contain volatile materials that have been mostly sealed off due to past cometary activity, i.e. due to significant loss of near-surface ices and the accumulation of a fallback dust blanket that form an insulating layer. Consequently, there are dormant comets and asteroids that share physical characteristics, e.g. reflectance, albedo, and polarization [4-6], making it challenging to determine whether a given asteroid is a dormant comet. However, one direct way of testing this is by searching for low levels of activity. A recent analysis of 75 dynamically-selected dormant comet candidates and six near-Sun asteroids applied machine learning techniques to search for activity by comparing predicted and measured V-band brightnesses. From this, only the near-Earth object (NEO) (3552) Don Quixote displayed signs of activity [7]. Further analysis of Spitzer molecular band emission observations confirmed Don Quixote as a weakly active comet [8].

Here we address the complexities of delineating these bodies in a related way by performing a comprehensive search for weak levels of extended emission in archival imaging of dormant comet candidates. We first selected ~ 3700 comet candidates by looking at asteroids in ‘classic’ Jupiter-family comet (JFC)-type orbits that have appropriate Jupiter-MOID values, and that have Tisserand parameters, T_J, < 3. We are currently developing software – the Remnant Emission Survey Tool (REST) – that will be able to automatically search through data archives, retrieve images of dormant comet candidates, and analyze their radial profiles to identify objects with possible extended emission. We will present preliminary results from the initial application of REST to several objects in our candidate list. For now, we are analyzing archival images taken by the Dark Energy Camera (DECam) instrument on the Cerro Tololo Inter-American (CTIO) Blanco 4-meter telescope in Chile [9]. Our study will ultimately be conducted for all the selected candidates, and will be expanded to include additional data archives. We are particularly interested in imaging that samples the gas coma – e.g. V- and g-band imaging at visible wavelengths,  and NEOWISE Channel 2 (4.5 µm) imaging [10]. Here, we will outline the developmental stages of REST, and present further initial findings from its early applications.

Acknowledgements: We extend our acknowledgements to the CTIO Blanco DECam Data Release 1 archive for providing the data utilized in this preliminary study. We also acknowledge support from NASA’s SSERVI program via award 80NSSC19M0214. References: [1] Jewitt, D. & Hsieh, H. H. (2024) in Comets III, 767 [2] Jewitt, D. et al. (2015) in Asteroids IV, 221 [3] Binzel, R. P. et al. (2015) in Asteroids IV, 243  [4] Chamberlin, A. B. et al. (1996) Icarus 119, 173 [5] Fernández, Y. R. et al. (2005) AJ 130, 308 [6] Geem, J. et al. (2022) A&A 658, A158.  [7] Mommert, M. et al. (2020) PSJ 1, 10. [8] Mommert, M. et al. (2020) PSJ 1, 12. [9] Dark Energy Survey Collaboration et al. (2016) MNRAS 460, 1270 [10] Mainzer, A. et al. (2011) ApJ 731, 53.