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
Copyright Elsevier

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.

¹Angela M.Dapremont,¹James J.Wray
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114299]
¹School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA, USA
Copyright Elsevier

Mud volcanism (MV) has been a proposed formation mechanism for positive-relief landforms in the lowland, equatorial, and highland regions of Mars. While visible and near-infrared (VNIR) spectroscopy has been used in a few cases to argue for the presence of MV on the surface of Mars, data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) remain underutilized. We conducted a global examination of proposed Mars MV features using CRISM VNIR data. We observe variable hydration states and place constraints on the composition of these features from orbit. We do not confidently identify phyllosilicates, carbonates, or sulfates associated with suggested Martian mud volcanoes. However, specific structures in Valles Marineris exhibit VNIR signatures consistent with unaltered hydrated glass of a volcanic origin and high-Ca pyroxene. CRISM visible data from MV features reveal consistent nanophase ferric oxide signatures on a global scale, although these signatures are not unique to Mars MV materials. Limitations in specific mineral detection are likely due to the fine grain size and/or textural characteristics of putative MV features. While we do not argue in favor of a specific proposed MV site in the context of future robotic or human missions, the insights of this study could be used as a guide for Mars surface exploration.