Infrared Spectra of Dark Asteroid Ryugu and Carbonaceous Chondrites

• Main Authors: Matsuoka, M., Nakamura, T., Hiroi, T., Kitazato, K., Senshu, H., Iwata, T., Abe, M., Amano, K., Kobayashi, S., Osawa, T., Ohtake, M., Matsuura, S., Arai, T., Komatsu, M., Nakato, A., Nakauchi, Y., Pilorget, C., Brunetto, R., Poulet, F., Riu, L., Domingue, D. L., Vilas, F., Takir, D., Palomba, E., Galiano, A., Milliken, R., Perna, D., Barucci, M. A., Bibring, J. P.
• Other Authors: Institut d'astrophysique spatiale (IAS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales Paris (CNES)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2019
• Subjects: 6008 Composition; PLANETARY SCIENCES: COMETS AND SMALL BODIES; 6045 Physics and chemistry of materials; 6207 Comparative planetology; PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS; 5410 Composition; PLANETARY SCIENCES: SOLID SURFACE PLANETS; [SDU]Sciences of the Universe [physics]; Ryugu; National Institute of Polar Research
• Online Access: https://hal.science/hal-03090408

International audience Near-infrared Spectrometer (NIRS3) onboard Hayabusa2 successfully obtained reflectance spectra of the C-type near-Earth asteroid Ryugu over a wavelength range of 1.8-3.2 µm. It was observed that Ryugu exhibits very low albedo (less than 0.02 at 2.0 μm), a slightly positive spectral slope, and an ubiquitous weak OH absorption band at 2.72 μm. These properties are nearly homogeneous across the asteroid surface. However, data of regions near the equator with ~40 m spatial resolution (~20 km altitude) exhibit variations in the 2.0-μm albedo that are possibly associated with geomorphological features. Reflectance values are higher near crater rims and lower in crater centers. Future updates to the photometric correction may change these apparent associations, but it is also observed that spectra of several flat areas without any obvious geomorphological features show relatively high reflectance (e.g., near 270, 300, and 350 degrees longitude, close to the equatorial ridge). If verified, the brighter areas could indicate surface materials that (a) are relatively carbon-poor, (b) have different physical properties, such as smaller grain size and/or decreased porosity, and/or (c) exhibit different forms/degrees of space weathering. Comparing spectra of carbonaceous chondrites with those of Ryugu shows that no meteorites are an ideal spectral match to Ryugu at all wavelengths. However, spectra of shocked or heated carbonaceous chondrites are most similar with their low albedo and weak, narrow OH absorption feature at 2.72 μm. Future lab analyses of samples returned from Ryugu will provide additional information on the mineralogical and chemical properties of Ryugu and how these relate to its spectral characteristics. Acknowledgements: We appreciate support from the National Institute of Polar Research for providing carbonaceous chondrites, the Japan Society for the Promotion of Science (JSPS) Core-to-Core Program "International Network of Planetary Sciences", the NASA Hayabusa2 Participating ...