Abstract We present a fully integrated model of cometary evolution that couples thermal and compositional processes with dynamical processes continuously, from formation to present-day activity. The combined code accounts for changes in orbital parameters that define the time-dependent heliocentric distance, which is fed into the thermal/compositional evolution code. The latter includes several volatile species, gas flow through the porous interior, crystallization of amorphous ice, sublimation and refreezing of volatiles in the pores. We follow the evolution of three models, with radii of 2, 10 and 50 km for 4.6 Gyr, through different dynamical epochs, starting near Neptune, moving to the Oort cloud (OC) and after a long sojourn there, back inward to the planetary region. The initial composition includes a mixture of CO, CO2 ices, amorphous water ice with trapped CO and CO2, and dust. We find that the CO ice is completely depleted in the small object, but preserved in the larger ones from a depth of 500 m to the center, while the CO2 and the amorphous ice are entirely preserved. Most importantly, the CO abundance profiles change as the cooling objects migrate to the OC. Upon return from the OC, the activity is driven by CO sublimation at large heliocentric distances (up to 50 au), by CO2 inward of 13 au and by gas released from amorphous ice at ~7 au. We find the effect of radioactive heating by long-lived isotopes to be negligible. Considering subsolar temperatures and limited active areas, we show that CO2 production can be detected even beyond 20 au.
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