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Optical, Infrared, and Radar Observations of 2015 JD1: Evidence of Surface Inhomogeneity

Presentation #415.01 in the session “Asteroids: NEO Individual Characterization”.

Published onOct 26, 2020
Optical, Infrared, and Radar Observations of 2015 JD1: Evidence of Surface Inhomogeneity

The inner regions of the main asteroid belt have been of particular interest due to its role as a body-delivery source to the near-Earth space. Much has been discussed about the mystery of the formation and evolution of objects that populate this region: E-types. Spectroscopic and dynamical analysis suggests that these objects originated from a highly-reduced parent body(ies). Their relation with the low-iron enstatite achondrite meteorites (aubrites) supports such formation conditions. We performed optical and near-infrared (NIR) observations of 2015 JD1 on 2019 October 31 at the Lowell Discovery Telescope (LDT). Radar observations were conducted at Arecibo Observatory on 2019 November 1 through November 3. Radar polarimetry measurements indicated a morphologically complex surface. The delay-Doppler images revealed a contact-binary (snowman-like) asteroid with an estimated diameter of about 150 m along the long axis. The disk-integrated high circular polarization ratio of 1.2 suggests a composition similar to E-types asteroids. The disk-integrated radar albedo of 29% suggests a moderate surface porosity. With an absolute magnitude H = 20.6 and our effective diameter, we derived a geometric albedo of 0.45 ± 0.05, consistent with E-types. The NIR and optical observation revealed featureless spectrums similar to E-types, consistent with radar, and an average g - r = 0.60 ± 0.03, respectively (g and r correspond to the average magnitude on each Sloan filter). We notice rotational NIR and optical color variabilities. The NIR spectral slope variability of 2015 JD1 is transitional: red positive-slopes spectra shifting to blue negative-slopes spectra and eventually transitioning back to red positive-slope. We notice a NIR slope difference of 40% from most-red to most-blue spectra. The reddish spectrums of 2015 JD1 points toward a surface rich in iron sulfide (troilite) while the bluish spectrums suggest a low-iron enstatite-rich region; minerals that perform aubrites bulk composition. The ongoing analysis suggests that such variation could be due to a surface “patch” slightly different in composition and grain sizes. Although no concrete conclusion has been established, it is clear that 2015 JD1 experienced either extreme formation conditions (accretion of fragments from multiple parent bodies or slightly heterogeneous parent body) or extreme surface evolution (space weathering) since its accretion. This work is supported in part by the Arizona Board of Regents and by NASA grant NNX15AF81G.

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