Horizons-CometScout – Enhancing Target Scouting for the Comet Interceptor Mission through the Vera C. Rubin Observatory

The ESA Comet Interceptor mission aims to perform a flyby of a Long Period Comet (ideally a Dynamically New Comet) or an Interstellar Object during its first passage through the inner Solar System.[1] Such targets are selected for their pristine state, as they have not been altered by any previous approach near the Sun and hence carry fundamental clues on the Solar System formation and evolution. Comet Interceptor requires an innovative methodology, as the target is likely to be identified only after the mission launch.[1] The upcoming Vera C. Rubin Observatory, with its Legacy Survey of Space and Time (LSST), will play a crucial role in the early detection of such Targets.  

Current estimates suggest that the Rubin Observatory will detect over five million new Solar System objects, addressing the current limitations in Long Period Comet (LPC) datasets. This represents a groundbreaking advancement, as existing records are presently characterised by a limited number of discoveries, non-homogeneous observation methodologies, and a lack of standardized data products across different surveys. To assessthe survey future impact, we developed Horizon-CometScout, a Python pipeline that evaluates LSST’s discovery potential by analysing how much earlier LSST would have discovered currently known comets if it had already been operational.[2] This tool provides a direct comparison with existing survey capabilities by estimating the improvement in detection epoch and distance for potential targets.  

Horizons-CometScout is a Python pipeline that combines JPL SBDB/Horizons information with Rubin LSST-like observability criteria to retrospectively screen known long-period and hyperbolic comets for their relevance to Comet Interceptor-like target searches.  

The pipeline automatically retrieves the list consisting of all Hyperbolic and Long Period Comets in the Horizons database. It identifies comets with reliable data for absolute luminosity M1 and the comet total magnitudeslope parameter k1, then it automatically flags comet according to the criteria in Table 3 of [3]. Moreover, a list of Comet Interceptor Potential target defined according to [2] is also obtained.  

The pipeline produces an historical set of observation for the 10 years prior to the perihelion epochs with an estimate of the apparent magnitude in the LSST r-band and check its observability from Rubin Observations. The estimation of LSST performance is further refined through synthetic source injections in Data Preview (DP0.2)[4] images available on the Rubin Science Platform, which simulate cometary appearances in LSST images, assessing the efficiency of available photometric tools in characterizing extended sources. 

We will present this tool and show its application to highlight how the Rubin Observatory’s capabilities will enhance the selection and study of pristine cometary targets well in advance of their perihelion passage,providing an advantageous lead time for opportune planning of the mission.  

References  

[1] Geraint H. Jones, Colin Snodgrass, Cecilia Tubiana, Michael Küppers, Hideyo Kawakita, Luisa M. Laraetal et al. The Comet Interceptor Mission. SpaceScienceReviews(2024)220:9 

[2] Laura Inno, Margherita Scuderi, Ivano Bertini, Marco Fulle, Elena Mazzotta Epifani, Vincenzo Della Corte, Alice Maria Piccirillo, Antonio Vanzanella, Pedro Lacerda, Chiara Grappasonni, et al. How much earlier would lsst have discovered currently known long-period comets? arXiv preprint arXiv:2412.12978, 2024.  

[3] C Snodgrass, E Mazzotta Epifani, C Tubiana, JP Sánchez, N Biver, L Inno, MM Knight, P Lacerda, J De Keyser, A Donaldson, et al. Considerations on the process of target selection for the comet interceptor mission. Icarus, page 116887, 2026. 

[4] O’Mullane, William, et al. "Data Preview 0.2 and Operations rehearsal for DRP." Vera C. Rubin Observatory Technical Note RTN-041 (2023).