[P-PS03] 太陽系小天体：太陽系の形成と進化における最新成果と今後の展望

[PPS03-05] Relationships between temperature distributions and thermal inertias of boulders observed by the low-altitude operation of the Hayabusa2

*大杉 歩^1,2、坂谷 尚哉²、嶌生 有理²、金丸　 仁明¹、石崎　 拓也²、千秋 博紀³、荒井 武彦⁴、出村 裕英⁵、神山 徹⁶、関口 朋彦⁷、田中 智^1,2、岡田 達明^2,1 (1.東京大学、2.宇宙航空研究開発機構 宇宙科学研究所、3.千葉工業大学、4.前橋工科大学、5.会津大学 、6.産業技術総合研究所、7.北海道教育大学)

キーワード：はやぶさ２、温度、岩塊、リュウグウ、TIR、熱慣性

The thermophysical properties of the C-type asteroid 162173 Ryugu were investigated using the Thermal Infrared Imager (TIR) onboard Hayabusa2 [1-3]. TIR can acquire thermal emission images from Ryugu to obtain the thermophysical properties of Ryugu's surface, TIR has a field of view of 16.7º× 12.7ºand an effective detector area of 328 × 248 pixels with a spatial resolution of about 0.051º per pixel [1,3]. Ryugu is a rubble pile body with a low bulk density and entirely covered with boulders, having a thermal inertia of 200-400 J m^-2 s ^-0.5 K^-1 (hereafter, tiu), which is low compared to 600-1000 tiu of typical carbonaceous chondrites [4,5]. However, there are still large uncertainties to determine the thermal inertia of irregularly shaped boulders. Here we analyzed TIR images taken at altitudes below 500 m during the release paths for the MINERVA rover (MNRV) on 21 September 2018 and the MASCOT lander (MSCT) on 3 October 2018, the 1st touchdown (TD1-L08E1) operation on 21 February 2019, the touchdown rehearsals (TD1-R1A) on 15 October 2018, and the decent operation for S01 (DO-S01) on 8 March 2019, and examined the temperature variation of a statistically significant number of boulders taken over an area of 100 pixels or larger, corresponding to several to tens of meters in diameter. These boulders have different temperatures from each other, and there were temperature distributions on the surface due to the geometry and the orientation of the asteroid. Nevertheless, we found that the temperatures in each area are Gaussian distributed and that most of the boulders in each area have similar thermal properties [6]. This suggests that the average temperature of each boulder reflects typical thermal properties. We will present the updates from our previous work [6], including a comparative study of temperature distributions and thermal inertia. Reference: [1] Okada T. et al., SSR, 208, 255 (2017), [2] Watanabe S. et al., Science 364, 268 (2019), [3] Okada T. et al., Nature 579, 518 (2020). [4] Shimaki Y. et al., Icarus 348, 113835 (2020). [5] Sakatani N. et al., Nat. Astron. 5, 766 (2021).[6] Ohsugi et al., JpGU Meeting 2022, PPS03-03