Presentation #112.04 in the session “Plenary Panel: Interstellar Objects and Active Small Bodies”.
Observing small active bodies at the earliest stages of activity before vigorous water-ice sublimation begins can help fill a critical knowledge gap concerning gas and dust emissions from these objects. Many of these objects exhibit long-term quiescent activity that is punctuated by sporadic outbursts or even fragmentation events. Models of nucleus structure and composition, as well as surface and subsurface activity, can be constrained by simultaneous measurements of gas and dust comae over a large range of heliocentric distances. Far from the Sun the sublimation and outgassing of hyper-volatiles, such as CO and CO2, becomes important, as does the amorphous-to-crystalline water-ice transition and mass wasting events, both of which can release trapped volatiles. The measured abundance ratios of CO/CO2 and other key species constrain models of nucleus activity and icy body formation and evolution. Centaurs, which are in the transition stage between Kuiper Belt objects and Jupiter family comets, are relevant, especially those which are passing through the dynamical Gateway region near Jupiter. We will review many active Centaurs, including 29P/Schwassmann-Wachmann 1, 2060 Chiron, 174P/ Echeclus, P/2010 C1 (Scotti) and the recently discovered P/2019 LD2 (ATLAS). We will also examine what observational constraints are provided from the distant activity of Jupiter Family Comets, (such as 159P/LONEOS and 103P/Hartley 2), and Oort Cloud comets (such as C/1995 O1 (Hale-Bopp), C/2010 U3 (Boattini), C/2016 R2 (PanSTARRS) and the currently inbound C/2017 K2 (PanSTARRS)). Since a very long baseline on heliocentric distance is needed to constrain the models, we will also review many valuable contributions from the amateur community for establishing a reliable long-term record of activity and make recommendations for constructing improved lightcurves and partnerships. This material is based in part on work done by M.W. while serving at the National Science Foundation and in part supported by NSF Grant No. AST-1945950.