1Gordon M.Gartrelle,2Paul S.Hardersen,3Matthew R.M.Izawa,4Matthew C.Nowinski
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114295]
1University of North Dakota, Grand Forks, ND, USA
2Trouvaille LLC, Tucson, AZ, USA
3Institute for Planetary Materials, Okayama University, Misasa, Japan
4George Mason University, Fairfax, VA, USA
D-type asteroids represent a complex mystery related to the accretional history, composition, and dynamical migration of Outer Solar System objects. These spectrally featureless bodies have revealed few clues while raising many questions over four decades. D-types are dark, difficult to observe and perhaps contain unaltered primordial material. D-type asteroids are abundant in the outer belt, dominant in the Jupiter Trojans, and rare in the inner belt as well as near Earth space. Material spectrally similar to D-types is pervasive on other outer solar system bodies as well. The appearance of dark, spectrally red material in multiple classes of small bodies suggests some unknown geochemical and/or evolutionary connection(s) may exist between them. Our investigation focused on the visible near-infrared (VNIR) (0.7–2.45 μm) spectral distinctions of D-types based on heliocentric location. Twenty-five newly acquired spectra from NASA’s Infrared Telescope Facility (IRTF) plus sixty-one IRTF VNIR spectra from the literature were combined into a single database and extensively analyzed with multiple orbital, observational, and spectral variables included in the examination. Twelve of the newly acquired spectra had not been imaged previously at IRTF.
Pearson’s correlation, simple and multiple regression, slope analysis, Monte Carlo modeling, 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 overall trend for the full slope. 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.