The Evolution of Water in Carbonaceous Main Belt Asteroids

Abstract

Astronomical signatures of water in the asteroid belt are found in the form of aqueously altered minerals and main-belt comets (MBCs). When paired with cosmochemical studies of meteorites, observations of aqueously altered minerals and MBCs may provide us with a way to constrain the availability of water during asteroid parent body accretion and thus constrain the position of the snow line in the early solar system. However, space weathering processes reduce our ability to accurately characterize asteroid compositions and match them with meteorite analogs. The goal of this dissertation is to study the role of water in space weathering processes, search for space weathering trends among C-complex asteroids, and characterize the mineralogy of two C-complex asteroid families. We simulate micrometeorite bombardment of C-complex minerals through the laser irradiation of Mg and Fe-end member phyllosilicates. We find that the minerals lizardite and cronstedtite show both an increase and decrease in spectral slopes as a function of irradiation. However, the overall spectral trends of these two minerals are notably different, and space weathering trends may vary with the degree of aqueous alteration experienced by an asteroid parent body. Our data show that dehydration of hydrous minerals is not necessary for space weathering processes to be e ective. We conducted an extensive telescopic survey of the Beagle and Themis asteroid families, and obtained one of the most comprehensive visible and near-infrared data sets on these asteroids to date. Our data suggest space weathering of C-complex asteroids occurs primarily at visible wavelengths, and results in an increase in spectral slopes and a decrease in albedo with age. Lastly, we explore the evolution of water ice in the main belt comet 133P/Elst-Pizarro. We use photometry data along with lightcurve inversion to constrain the pole orientation of 133P/Elst-Pizarro. We use the resulting obliquity ( 75 ) to model the evolution of subsurface ice for a variety of grain sizes and dynamical ages. This dissertation utilizes the strength of observational, experimental, and model data to provide valuable insights on the thermal and aqueous evolution of carbonaceous main belt asteroids.