Active Centaurs in Context: understanding future members of the Jupiter family comets

The short period Jupiter family comets (JFCs), some of the solar system’s most active small bodies, originate in the distant, cold trans-Neptunian region. Understanding their orbital evolution from beyond Neptune, through the giant planet region as Centaurs, and into the inner solar system as JFCs provides critical context for the thermal and physical processes that drive cometary activity and alter their surfaces. In the last few decades, it has become increasingly clear that activity begins beyond Jupiter. Centaurs have been observed to have gas comas (e.g., 29P/SW1), to experience outburst events (e.g., 29P/SW1, Echeclus), and to have orbiting debris (e.g., Chiron, Chariklo). A recent detailed analysis of the dynamical evolution of Centaurs identified an orbital “Gateway”, a relatively low-eccentricity orbit just beyond Jupiter, through which the majority of objects that will become JFCs pass before they reach the smaller heliocentric distances where water-driven activity occurs (Sarid, Volk, Steckloff, et al. 2019). This important dynamical transition region coincides with the heliocentric distances where outgassing and cometary activity driven by more volatile species like CO are observed to occur. The recently discovered active Centaur P/2019 LD2 (ATLAS) is an excellent example of an object near the Gateway whose recent orbital and thermal history is consistent with very recent onset of activity (Steckloff, Sarid, Volk, et al. 2020). Its imminent dynamical transition into the JFC population in 2063 (Kareta, Volk, Noonan, et al. 2020) makes 2019 LD2 a high priority target for observational characterization. The gateway region represents a critical opportunity for remote observations and possibly in-situ exploration to characterize the initial onset of activity that eventually transforms pristine outer solar system objects like Arrokoth into highly evolved cometary nuclei like 67P/CG.