  Comets and small Kuiper belt objects are considered to be among the most
primitive objects in the solar system as comets like C/1995 O1 Hale-Bopp are
rich in highly volatile ices like CO. It has been suggested that early in the
solar system evolution the precursors of both groups, the so-called icy
planetesimals, were modified by both short-lived radiogenic heating and
collisional heating. Here we employ 2D finite-difference numerical models to
study the internal thermal evolution of these objects, where we vary formation
time, radius and rock-to-ice mass fraction. Additionally we perform 3D SPH
collision models with different impact parameters, thus considering both
cratering and catastrophic disruption events. Combining the results of both
numerical models we estimate under which conditions highly volatile ices like
CO, CO2 and NH3 can be retained inside present-day comets and Kuiper belt
objects. Our results indicate that for present-day objects derived from the
largest post-collision remnant the internal thermal evolution controls the
amount of remaining highly volatile ices, while for the objects formed from
unbound post-collision material the impact heating is dominant. Finally we
apply our results to present-day comets and Kuiper belt objects like
67P/Churyumov-Gerasimenko, C/1995 O1 Hale-Bopp and (486958) Arrokoth.
