講演情報
[PPS03-P02]Spectral analysis of craters on Ryugu using global and close-up observation by multi-instrument data
*森田 朋代1、巽 瑛理2、市川 真弓3、筒井 皓基1、石田 世実1、髙瀬 大河1、川田 理栄仁1、中村 智樹1 (1.国立大学法人東北大学、2.カナリア天体物理学研究所、3.宇宙航空研究開発機構)
キーワード：
Hayabusa2、リモートセンシング、反射スペクトル、クレーター
Introduction: The Hayabusa2 mission conducted remote-sensing observations of the asteroid Ryugu over a wide range of spatial scales, from global mapping at ~20 km high to close-up observations at altitudes below 1 km. Impact craters are key to understanding the evolutionary history of an asteroid’s surface. The Small Carry-on Impactor (SCI) experiment, which successfully created an artificial crater on Ryugu [1], revealed that the surface is affected by space-weathering processes such as solar wind irradiation and micrometeoroid bombardment, whereas the subsurface contains fresher materials. The experiment also suggested that subsurface materials are composed of finer-grained particles than those at the surface [1]. In this study, we reassess natural craters on Ryugu to investigate their spectral characteristics and to better understand the evolutionary processes.
Methodology: We analyzed the spectral properties of natural craters on Ryugu using image and spectral data obtained by ONC-T, NIRS3, and TIR onboard Hayabusa2. Six parameters were extracted: (1) albedo at v-band (0.55 µm), (2) spectral slope in the b-x band (0.48–0.86 µm), (3) 2-µm reflectance, (4) spectral slope in the 2.1–2.5 µm range, (5) absorption depth at 2.7 µm, and (6) thermal inertia [2]. The crater dataset includes those cataloged by Hirata et al. (2020) [3] and Cho et al. (2021) [4], as well as additional small craters with diameters ≦ 15 m that were newly identified in this study using high-resolution ONC-T image data.
Result and discussion: The extracted six spectral and physical properties show small variations among craters and generally exhibit values comparable to those of the surrounding regolith, consistent with previous studies suggesting that Ryugu’s surface is globally homogeneous [5]. However, correlations are observed between crater diameter and four spectral parameters: (1) albedo at the v-band, (2) spectral slope in the b-x band, (3) 2 µm reflectance, and (4) spectral slope in the 2.1–2.5 µm range. Note that these spectral indicators are sensitive to surface physical properties such as grain size and porosity [6], as well as to compositional and structural modifications caused by space weathering [7]. In this presentation, we discuss the possibility that the spectral characteristics of craters on Ryugu’s surface cannot be explained solely by grain-size effects and instead reflect the influence of space weathering.
Reference
[1] Arakawa et al., 2020, Science 368, 67-71. [2] Shimaki et al., 2021, Icarus. [3] Hirata et al., 2020, Icarus 338, 113527. [4] Cho et al., 2021, J. Geophys. Res. Planets, 126(8) [5] Kitazato et al., 2019, Science 364, 272-275. [6] Cantillo et al., 2023, Planet. Sci. J. 4(9), 177. [7] Matsuoka et al., 2023, Commun. Earth Envron., 4(1), 355.
Acknowledgment
This work was supported by Hayabusa2# International Visibility Enhancement Project. We thank senior associate professor N. Hirata for technical support.
Methodology: We analyzed the spectral properties of natural craters on Ryugu using image and spectral data obtained by ONC-T, NIRS3, and TIR onboard Hayabusa2. Six parameters were extracted: (1) albedo at v-band (0.55 µm), (2) spectral slope in the b-x band (0.48–0.86 µm), (3) 2-µm reflectance, (4) spectral slope in the 2.1–2.5 µm range, (5) absorption depth at 2.7 µm, and (6) thermal inertia [2]. The crater dataset includes those cataloged by Hirata et al. (2020) [3] and Cho et al. (2021) [4], as well as additional small craters with diameters ≦ 15 m that were newly identified in this study using high-resolution ONC-T image data.
Result and discussion: The extracted six spectral and physical properties show small variations among craters and generally exhibit values comparable to those of the surrounding regolith, consistent with previous studies suggesting that Ryugu’s surface is globally homogeneous [5]. However, correlations are observed between crater diameter and four spectral parameters: (1) albedo at the v-band, (2) spectral slope in the b-x band, (3) 2 µm reflectance, and (4) spectral slope in the 2.1–2.5 µm range. Note that these spectral indicators are sensitive to surface physical properties such as grain size and porosity [6], as well as to compositional and structural modifications caused by space weathering [7]. In this presentation, we discuss the possibility that the spectral characteristics of craters on Ryugu’s surface cannot be explained solely by grain-size effects and instead reflect the influence of space weathering.
Reference
[1] Arakawa et al., 2020, Science 368, 67-71. [2] Shimaki et al., 2021, Icarus. [3] Hirata et al., 2020, Icarus 338, 113527. [4] Cho et al., 2021, J. Geophys. Res. Planets, 126(8) [5] Kitazato et al., 2019, Science 364, 272-275. [6] Cantillo et al., 2023, Planet. Sci. J. 4(9), 177. [7] Matsuoka et al., 2023, Commun. Earth Envron., 4(1), 355.
Acknowledgment
This work was supported by Hayabusa2# International Visibility Enhancement Project. We thank senior associate professor N. Hirata for technical support.