The compositional variation of small bodies across the Solar System

Small bodies hold keys to our understanding of the Solar System. By studying these populations we seek the information on the conditions and structure of the primordial and current Solar System, its evolution, and the formation process of the planets. Constraining the surface composition of small bodies provides us with the ingredients and proportions for this cosmic recipe. This thesis, comprised of studies of inner and outer Solar System small bodies, is dedicated to understanding the compositional gradient across the Solar System through spectroscopic and photometric measurements. I present a taxonomy of visible and near-infrared spectral data based on 371 asteroid spectra. The taxonomy consists of 24 classes that best categorize the spectral variation seen among inner Solar System small bodies. From the creation of this taxonomy we learn that with only visible wavelength data there is uncertainty in shape of the 1-$\mu$m band. While near-infrared wavelength range is excellent for interpreting data containing diagnostic 1- and 2-$\mu$m bands, the more subtly featured C- and X-complexes appear to be largely degenerate in this wavelength regime. I analyze the photometric colors of 23 Transneptunian Objects and Centaurs, nine of which have never been previously observed, and assign them taxonomic classifications. I discuss objects that either have changed classes from previous data or have significant changes in absolute magnitude. Furthermore, I interpret the surface composition of three outer Solar System small bodies, Jupiter-coupled object (52872) Okyrhoe, and TNOs (90482) Orcus and (73480) 2002 PN$_{34}$, by modeling spectroscopic measurements in the visible and near-infrared wavelength ranges. The spectra reveal varying amounts of H$_2$O ice among these bodies. For Orcus I provide rough constraints for the presence of materials more volatile than water ice. I present a search for solid ethane, C$_2$H$_6$, on the surfaces of Pluto and Triton, based on near-infrared spectral observations. I model each surface using a radiative transfer model based on Hapke theory \citep{Hapke1993} with three basic models: without ethane, with pure ethane, and with ethane diluted in nitrogen. While the presence of less than a few percent of ethane cannot be excluded on both bodies, there is no strong detection on either. Finally, I review the current knowledge of the compositional distribution of material in our Solar System, providing the global view of small bodies. I particularly focus on the presence of water in all its phases which is especially pertinent our understanding of our own planet, Earth, and the life on it. I briefly compare the general structure of our Solar System to other imaged debris disks to put into perspective the detailed, though narrow, view of our own Solar System with the broad, low resolution view of others.