Potential Backup Targets for Comet Interceptor

Comet Interceptor (Snodgrass & Jones 2019) is an ESA (European Space Agency) F-class (Fast) mission expected to launch in 2028 on the same launcher as ESA's ARIEL (Atmospheric Remote-sensing Infrared Exoplanet Large-survey; Tinetti et al. 2016) mission. Comet Interceptor's science payload consists of three spacecraft, a primary spacecraft that will carry two smaller probes to be released at the target. The three spacecraft will y-by the target along different chords, providing multiple simultaneous perspectives of the comet nucleus and its environment. Each of the spacecraft will be equipped with different but complementary instrument suites designed to study the far and near coma environment and surface of a comet or interstellar object (ISO), a rogue planetesimal formed around another star system passing through the Solar System The primary spacecraft will perform a y-by at ~1000 km from the target. The two smaller probes will travel deeper into the coma, closer to the nucleus. The mission is being designed and launched without a specific comet designated as its main target. Comet Interceptor will travel to the Sun-Earth L2 Lagrangian point with ARIEL and wait in hibernation until a suitable long-period comet (LPC) is found that will come close enough to the Sun for the spacecraft to maneuver to an encounter trajectory. Ideally, the mission will visit a dynamically new comet (DNC), a LPC on its first entry into the the inner Solar System from the Oort cloud, or an ISO. Since 1970, 23% of LPCs discovered with q<3.1 au are DNCs (Krolikowska & Dybczynski 2019). Comet Interceptor's encounter target will mostly likely be discovered in the 2020s with the onset of the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST; Ivezic et al. 2019). Over its 10-year baseline survey, LSST is expected to find ~10,000 new comets (Solontoi et al. 2010) and to discover several ISOs per year (e.g., Cook et al. 2016; Rice & Laughlin 2019).