Surface Composition of Asteroid 269 Justitia: Insights from Spectral Mixture Modeling

Abstract Asteroid (269) Justitia is one of the more unusual asteroids in the main belt due to its extremely red spectral slope at visible and near infrared (VNIR) wavelengths. While the surface composition of (269) Justitia remains uncertain due to a lack of diagnostic absorption features in the VNIR region, intriguing clues to its nature are provided by recent mid- and thermal-infrared wavelength observations (MIR and TIR, respectively). In the VNIR, no identifiable analogs to Justitia can be found among the known meteorites. Instead, the best spectral matches come from Trans-Neptunian Objects (TNOs), possibly suggesting a genetic relationship with those bodies. On the other hand, recent TIR emissivity spectra reveal the likely presence of fine-grained anhydrous silicates on Justitia’s surface, possibly inconsistent with a TNO origin. To explore this issue, we used a radiative transfer mixing model to investigate the spectral nature of Justitia in the VNIR and TIR. In the VNIR, our results are consistent with mixtures of space weathered silicates and carbonaceous material, though the presence of complex organics cannot be ruled out. In the TIR, our results favor either carbonaceous material or a mixture of space-weathered silicates and carbonaceous components. The best spectral match to Justitia’s spectra was found by blending carbonaceous material with moderate to extensively space-weathered silicates. This combination could, in turn, indicate a potential collision between silicate-rich and carbonaceous bodies during the early history of Justitia.