TY - JOUR
T1 - Characterization of the Ryugu surface by means of the variability of the near-infrared spectral slope in NIRS3 data
AU - Galiano, A.
AU - Palomba, E.
AU - D'Amore, M.
AU - Zinzi, A.
AU - Dirri, F.
AU - Longobardo, A.
AU - Kitazato, K.
AU - Iwata, T.
AU - Matsuoka, M.
AU - Hiroi, T.
AU - Takir, D.
AU - Nakamura, T.
AU - Abe, M.
AU - Ohtake, M.
AU - Matsuura, S.
AU - Watanabe, S.
AU - Yoshikawa, M.
AU - Saiki, T.
AU - Tanaka, S.
AU - Okada, T.
AU - Yamamoto, Y.
AU - Takei, Y.
AU - Shirai, K.
AU - Hirata, N.
AU - Matsumoto, K.
AU - Tsuda, Y.
N1 - Funding Information:
The Hayabusa2 spacecraft was developed and built under the leadership of Japan Aerospace Exploration Agency (JAXA), with contributions from the German Aerospace Center (DLR) and the Centre National d'Études Spatiales (CNES), and in collaboration with NASA, Nagoya University, University of Tokyo, National Astronomical Observatory of Japan (NAOJ), University of Aizu, Kobe University, and other universities, institutes, and companies in Japan. We also thank the engineers who contributed to the success of Hayabusa2 operations. This work is founded by the Italian Space Agency (ASI) and it has been developed under the agreement 2018-27-HH-0.
Publisher Copyright:
© 2020 Elsevier Inc.
PY - 2020/11/15
Y1 - 2020/11/15
N2 - The Near-Earth Asteroid 162173 Ryugu (1999 JU3) was investigated by the JAXA Hayabusa2 mission from June 2018 to November 2019. The data acquired by NIRS3 spectrometer revealed a dark surface with a positive near-infrared spectral slope. In this work we investigated the spectral slope variations across the Ryugu surface, providing information about physical/chemical properties of the surface. We analysed the calibrated, thermally and photometrically corrected NIRS3 data, and we evaluated the spectral slope between 1.9 μm and 2.5 μm, whose values extend from 0.11 to 0.28 and the mean value corresponds to 0.163±0.022. Starting from the mean value of slope and moving in step of 1 standard deviation (0.022), we defined 9 “slope families”, the Low-Red-Slope families (LR1, LR2 and LR3) and the High-Red-Sloped families (HR1, HR2, HR3, HR4, HR5, HR6). The mean values of some spectral parameters were estimated for each family, such as the reflectance factor at 1.9 μm, the spectral slope, the depth of bands at 2.7 μm and at 2.8 μm. A progressive spectral reddening, darkening and weakening/narrowing of OH bands is observed moving from the LR families to the HR families. We concluded that the spectral variability observed among families is the result of the thermal metamorphism experienced by Ryugu after the catastrophic disruption of its parent body and space weathering processes that occurred on airless bodies as Ryugu, such as impact cratering and solar wind irradiation. As a consequence, the HR1, LR1, LR2 and LR3 families, corresponding to equatorial ridge and crater rims, are the less altered regions on Ryugu surface, which experienced the minor alteration and OH devolatilization; the HR2, HR3, HR4, HR5 families, coincident with floors and walls of impact craters, are the most altered areas, result of the three processes occurring on Ryugu. The strong reddening of the HR6 family (coincident with Ejima Saxum) is likely due to the fine-sized material covering the large boulder.
AB - The Near-Earth Asteroid 162173 Ryugu (1999 JU3) was investigated by the JAXA Hayabusa2 mission from June 2018 to November 2019. The data acquired by NIRS3 spectrometer revealed a dark surface with a positive near-infrared spectral slope. In this work we investigated the spectral slope variations across the Ryugu surface, providing information about physical/chemical properties of the surface. We analysed the calibrated, thermally and photometrically corrected NIRS3 data, and we evaluated the spectral slope between 1.9 μm and 2.5 μm, whose values extend from 0.11 to 0.28 and the mean value corresponds to 0.163±0.022. Starting from the mean value of slope and moving in step of 1 standard deviation (0.022), we defined 9 “slope families”, the Low-Red-Slope families (LR1, LR2 and LR3) and the High-Red-Sloped families (HR1, HR2, HR3, HR4, HR5, HR6). The mean values of some spectral parameters were estimated for each family, such as the reflectance factor at 1.9 μm, the spectral slope, the depth of bands at 2.7 μm and at 2.8 μm. A progressive spectral reddening, darkening and weakening/narrowing of OH bands is observed moving from the LR families to the HR families. We concluded that the spectral variability observed among families is the result of the thermal metamorphism experienced by Ryugu after the catastrophic disruption of its parent body and space weathering processes that occurred on airless bodies as Ryugu, such as impact cratering and solar wind irradiation. As a consequence, the HR1, LR1, LR2 and LR3 families, corresponding to equatorial ridge and crater rims, are the less altered regions on Ryugu surface, which experienced the minor alteration and OH devolatilization; the HR2, HR3, HR4, HR5 families, coincident with floors and walls of impact craters, are the most altered areas, result of the three processes occurring on Ryugu. The strong reddening of the HR6 family (coincident with Ejima Saxum) is likely due to the fine-sized material covering the large boulder.
KW - Hayabusa2
KW - Near-earth asteroid
KW - NIR spectral slope
KW - Ryugu
KW - Space weathering
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U2 - 10.1016/j.icarus.2020.113959
DO - 10.1016/j.icarus.2020.113959
M3 - Article
AN - SCOPUS:85088093374
SN - 0019-1035
VL - 351
JO - Icarus
JF - Icarus
M1 - 113959
ER -