Conférence - David Nesvorný : Following Comets to Their Distant Source Reservoirs and Back

Alessandro MorbidelliChaire Chaire Formation planétaire : de la Terre aux exoplanètesCollège de FranceAnnée 2025-2026David NesvornýConférence - David Nesvorný : Following Comets to Their Distant Source Reservoirs and BackDavid NesvornýSouthwest Research Institute, USARésuméComets are icy bodies that originate in the trans-Neptunian region and evolve into the inner Solar System, where they become active due to the sublimation of water ice triggered by solar heating. We describe dynamical models that trace the implantation of comets into their distant source reservoirs during the early Solar System, approximately 4.6 billion years ago. These models are used to predict the present-day orbital distribution and number of active comets, which are then compared to observational data. The results indicate that the scattered disk and the Oort cloud are the primary source reservoirs for ecliptic comets (short-period) and isotropic comets (long-period and Halley-type), respectively. The observed orbital distribution of ecliptic comets is well reproduced if their physical lifetimes are limited to a few hundred perihelion passages within 2.5 astronomical units of the Sun. In contrast, small Oort-cloud comets tend to be more active and typically disintegrate after only a few such passages. Halley-type comets appear to represent an extension of the population of large, returning Oort-cloud comets to shorter orbital periods. We explore how the dynamical structure of cometary reservoirs is affected by the Galactic tide and Sun's birth environment within a stellar cluster.