[P-PS03] Regolith Science

[PPS03-10] Local variation in thermal inertia around the artificial impact crater on Ryugu

*Naoya Sakatani¹, Satoshi Tanaka², Tatsuaki Okada², Toru Kouyama³, Akira Miura², Naru Hirata⁴, Hiroki Senshu⁵, Takehiko Arai⁶, Yuri Shimaki², Hirohide Demura⁴, Tomohiko Sekiguchi⁷, Jun Takita⁸, Tetsuya Fukuhara¹, Thomas Müller⁹, Axel Hagermann¹⁰, Jens Biele¹¹, Matthias Grott¹¹, Maximillian Hamm^11,12, Marco Delbo¹³, Masahiko Arakawa¹⁴, Kazunori Ogawa¹⁵, Koji Wada⁵, Toshihiko Kadono¹⁶, Rie Honda¹⁷, Kei Shirai¹⁴, Takanao Saiki², Hiroshi Imamura², Yasuhiko Takagi¹⁸, Hajime Yano², Masahiko Hayakawa², Hirotaka Sawada², Satoru Nakazawa², Seiji Sugita¹⁹, Tomokatsu Morota¹⁹, Manabu Yamada⁵, Shingo Kameda¹, ERI TATSUMI²⁰, Yasuhiro Yokota², Hidehiko Suzuki²¹, Kazuo Yoshioka¹⁹, Moe Matsuoka², Yuichiro Cho² (1.Rikkyo University, 2.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3.National Institute of Advanced Industrial Science and Technology, 4.University of Aizu, 5.Chiba Institute of Technology, 6.Ashikaga University, 7.Hokkaido University of Education, 8.Hokkaido Kitami Hokuto High School, 9.Max-Planck Institute for Extraterrestrial Physics, 10.Luleå University of Technology, 11.German Aerospace Center, 12.University of Potsdam, 13.Observatoire de la Côte d'Azur, CNRS, 14.Kobe University, 15.JAXA Space Exploration Center, Japan Aerospace Exploration Agency, 16.University of Occupational and Environmental Health, 17.Kochi University, 18.Aichi Toho University, 19.University of Tokyo, 20.Instituto de Astrofisica de Canarias, 21.Meiji University)

The Hayabusa2 spacecraft has completed the rendezvous phase around Cb-type asteroid Ryugu in 2019. From thermal infrared imaging by TIR, global temperature distribution of Ryugu is consistent with the thermal calculation with thermal inertia of 300±100 J m^-2 K^-1 s^-0.5 [1], and thermal inertia values of the floors of craters are in general roughly comparable with the global average [2]. On the other hand, few small and fresh craters show anomalously low thermal inertia less than 100 J m^-2 K^-1 s^-0.5, contributed from the highly porous nature of boulders exposed by the impact cratering [3]. On April 2019, Hayabusa2 performed an artificial impact (Small Carry-on Impactor or SCI) experiment [4], whereby a ~2 kg mass was fired at 2 km/s against the asteroid surface. As a result of the successful operation, an artificial crater (SCI crater) with diameter larger than 10 m was created on the asteroid.

In the preliminary analysis of TIR data of the SCI crater, we suggested no thermally-anomalous materials on the crater floor [3]. In other words, the SCI crater has similar thermal inertia with the global average, and physical properties of the subsurface materials are similar to that of the top surface, at least on the SCI impact site. However, regional difference in the thermal inertia inside and outside the SCI crater have not been discussed. We will present whether the regional variation of the thermophysical properties appears around the SCI craters.

References: [1] Okada et al. (2020), Nature 579, 518-522. [2] Shimaki et al. (2020), Icarus 348, 113835. [3] Sakatani et al. (2021), LPSC #1832, #2189. [4] Arakawa et al. (2020), Science 368, 67-71.