Date of Award
Doctor of Philosophy (PhD)
James G. Casler
D-type asteroids represent a complex mystery related to the history, compositional chemistry, and dynamical migration of Outer Solar System objects. These spectrally featureless bodies have revealed few clues while raising many questions over four decades. This investigation focused on the VNIR (0.7-2.45 μm) spectral distinctions of D-types based on heliocentric location, the surface composition of D-types, and a parent body search for ungrouped chondrites Tagish Lake (TLM) and WIS 91600 long suspected as D-type analogs. Twenty-five newly acquired spectra from NASA/IRTF plus sixty-one IRTF VNIR spectra from the literature were combined into a single database and extensively analyzed.
Correlation, simple and multiple regression, slope analysis, Monte Carlo, as well as Principal Component Analysis (PCA) determined D-types show increased reddening with decreasing distance, with the segment from 1.5-2.45 μm, driving the trend for the full slope. The low end of the wave range (0.7-1.35 μm) exhibits an opposite trend of increasing redness with increasing distance. Principal components show strong connection to the 0.7-1.35 μm slope and inclination of D-type Jupiter Trojans. Principal component combinations, magnitudes, and positive/negative direction relate strongly to both observed and derived differences in the D-type L4 and L5 Trojan population. The L5 population is less evolved spectrally and dynamically than L4 counterparts perhaps due to lower dynamical instabilities inside the L4 cloud.
Surface compositional modeling with Shkuratov radiative transfer theory suggests D-type surfaces are composed of combinations of iron-poor olivine, magnesium-rich saponite, magnetite, siderite, calcite, dolomite, plus, varying combinations of opaques and H2O ice. This is similar bulk chemistry to the ungrouped chondrites and supports D-types as their parent bodies. Extensive parent body analysis concludes the near-Earth asteroid (NEA) 17274 (2000 LC16) is a plausible parent body for TLM, but a similar search for WIS 91600 proved inconclusive. This study of spectral and geochemical properties of D-type asteroids has delivered a wealth of information to better understand the evolution of dark objects in the Outer Solar System, surface mineral chemistry, and characteristics of parent bodies. It will serve as useful input for corollary studies as well as NASA’s upcoming Lucy Mission to the Jupiter Trojans.
Gartrelle, Gordon M., "Spectral Variations Of D-Type Asteroids At Different Heliocentric Distances" (2019). Theses and Dissertations. 2850.