Multivariable statistical analysis of spectrophotometry and spectra of (162173) Ryugu as observed by JAXA Hayabusa2 mission

Barucci, M. A.; Hasselmann, P. H.; Fulchignoni, M.; Honda, R.; Yokota, Y.; Sugita, S.; Kitazato, K.; Deshapriya, J. D. P.; Perna, D.; Tatsumi, E.; Domingue, D.; Morota, T.; Kameda, S.; Iwata, T.; Abe, M.; Ohtake, M.; Matsuura, S.; Matsuoka, M.; Hiroi, T.; Nakamura, T.; Kouyama, T.; Suzuki, H.; Yamada, M.; Sakatani, N.; Honda, C.; Ogawa, K.; Hayakawa, M.; Yoshioka, K.; Cho, Y.; Sawada, H.; Takir, D.; Vilas, F.; Hirata, N.; Hirata, N.; Tanaka, S.; Yamamoto, Y.; Yoshikawa, M.; Watanabe, S.; Tsuda, Y.
Bibliographical reference

Astronomy and Astrophysics, Volume 629, id.A13, 10 pp.

Advertised on:
9
2019
Number of authors
39
IAC number of authors
1
Citations
14
Refereed citations
14
Description
Context. Starting from late June 2018, the JAXA asteroid sample return mission Hayabusa2 acquired a large quantity of resolved images and spectra of the surface of the asteroid (162173) Ryugu. Aims: By studying the visible and near-infrared spectral behavior across the surface of Ryugu using a statistical analysis, we aim to distinguish spectral homogeneous groups and to detect the small heterogeneities. This allows us to better constrain the surface composition variations. Methods: In order to isolate and interpret the difference in the asteroid surface spectral behavior, we applied the G-mode multivariate statistical analysis to a set of pixels containing information of (i) the visible ONC-T spectrophotometry, and (ii) the near-infrared NIRS3 spectra thereby obtaining automatic statistical clustering at different confidence levels. Results: The analysis of both ONC-T and NIRS3 data allows us to highlight small spectral variations on the Ryugu surface. At a 3σ confidence level, only two groups are evident, while going down to 2σ more groups are obtained with differences in spectral slope and band depth. Conclusions: The identified groups have been associated with main morphological surface features. The spectral slope variations that characterize the small groups obtained by ONC-T data analysis, are interpreted as a consequence of space weathering with the presence of more or less fresh material and/or the different grain sizes of the regolith. The variations found analyzing the NIRS3 data are attributed to slightly different contents of hydrated material and different regolith sizes. The distribution on the Ryugu surface of the groups obtained by the analysis of the two instruments indicates a clear spectral dichotomy both between the east and west, and the north and south hemispheres. Small sized regolith grains associated to the redder spectra seem concentrated in the southwestern part of the body.
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Minor Bodies of the Solar System
This project studies the physical and compositional properties of the so-called minor bodies of the Solar System, that includes asteroids, icy objects, and comets. Of special interest are the trans-neptunian objects (TNOs), including those considered the most distant objects detected so far (Extreme-TNOs or ETNOs); the comets and the comet-asteroid
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