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Abstract
The study of the Solar System's remnant planetesimals is motivated by their connection with their formation conditions in the proto-Solar disk. The discovery of the active Centaurs and Main Belt Comets over the past few decades has made it clear that far more objects are go through phases of activity than previously estimated, and often through activity mechanisms that are poorly understood. The critical knowledge gap is thus understanding how activity changes the properties of these small bodies and how to interpret their modern properties to understand their recent evolution. This Dissertation improves our ability to ``roll back the clock" on these small bodies through telescopic observations, dynamical simulations, and laboratory experiments relevant to nine objects at different evolutionary and activity states to assess how changes in activity alter the properties of these objects. Telescopic observations of two Geminid Complex objects, (3200) Phaethon and (155140) 2005 UD, reveal Phaethon's surface to be rotationally homogeneous but different from UD's. I heated samples of the CI Chondrite Orgueil to successively higher temperatures to compare with the reflectance spectra of these objects and constrain their recent thermal evolution. Laboratory spectra at Phaethon's perihelion temperature were quite similar to Phaethon, but no match was found for UD. Observations of the nuclei of four (nearly-) dormant traditional comets, including the Quadrantid parent (196256) 2003 EH$_1$, show them to have a large variation in surface properties. Dormant Main Belt Comets might be distinguishable from dormant traditional comets, but thermal alteration might play a complicating role for some objects. Orbital simulations and new multi-wavelength telescopic observations of two active Centaurs, 174P/Echeclus and P/2019 LD2 (ATLAS), show them to have very different activity patterns and recent orbital evolutions. Echeclus's activity is dominated by strong, short-lived outbursts, while LD2's activity is weak and stable in time. LD2's recent orbital change might have initiated its activity, but Echeclus has had no significant recent orbital changes. I also present and analyze observations of the interstellar comet 2I/Borisov, which reveal it to be compositionally distinct from many Solar System comets despite many clearly similar ongoing chemical processes.
