Implications of Non-Compositional Effects on Spectral Characterization of Natural and Artificial Space Objects

Abstract

The study of near-Earth asteroids (NEAs) is one of a few sub-disciplines of astronomy and planetary science that offers researchers the thrill of acquiring tangible samples related to their astronomical targets. Furthermore, these studies can help better understand impactor threats to life on Earth and have real and actionable consequences. Although the official mandates for NASA are to detect, track, and characterize NEAs larger than 140 m, characterization lags behind the pace of detection despite being crucial for understanding the threat posed by these targets. Visible and near-infrared (NIR) spectroscopy can provide information about asteroid surface properties, including specific minerals present on the surface. Spectroscopic measurements can be altered, however, by both observational and physical, non-compositional effects that may distort the analysis of the asteroid’s surface. Among these alteration effects are grain size variations, metal content, shock darkening, space weathering, and phase angle. This dissertation explores a selection of these alteration effects (shock darkening, space weathering, phase angle) using laboratory studies of meteorites, visible to NIR spectroscopy and photometry of asteroids, and visible spectroscopy of geostationary satellites. The studies presented here represent hundreds of nights of observations and the development of a visible spectroscopy data processing pipeline. Results include the first evidence of observed shock darkening on the surface of an NEA, multi-year spectral monitoring of an active asteroid to test space weathering hypotheses, and an atlas of spectral phase variations in geostationary satellites visible from Tucson, AZ. In addition to probing these spectral alteration effects, these studies also reveal interesting implications for the H chondrite parent body and provide a baseline of artificial object spectra for differentiating between natural and artificial objects in near-Earth space. Although these results are very useful, they also highlight the ongoing need for NEA characterization work. Additional studies of space weathering are especially critical since this is often invoked for explaining asteroid spectral features, but the effects on asteroids are not fully understood.