[P-PS03] Small Solar System Bodies: Latest results and new perspectives on the Solar System evolution

[PPS03-P09] Corrected Temperature Map on Shape Model of Ryugu observed by Thermal Infrared Imager onboard Hayabusa2

*Takehiko Arai¹, Tatsuaki Okada^2,3, Satoshi Tanaka², Hirohide Demura⁴, Toru Kouyama⁵, Naoya Sakatani⁶, Yuri Shimaki², Hiroki Senshu⁷, Tomohiko Sekiguchi⁸, Masanori Kanamaru², Takuya Ishizaki² (1.Maebashi Institute of Technology, 2.Japan Aerospace Exploration Agency, 3.The University of Tokyo, 4.The University of Aizu, 5.National Institute of Advanced Industrial Science and Technology, 6.Rikkyo University, 7.Chiba Institute of Technology, 8.Hokkaido University of Education)

Keywords:Hayabusa2, Thermal Infrared Imager, Shape Model

The Thermal Infrared Imager (TIR) onboard Hayabusa2 carried out observations of the asteroid 162173 Ryugu in 2018 and 2019 (Okada et al., 2020). TIR globally determined the brightness temperature of the Ryugu surface. The thermal inertia maps on the Ryugu were derived from the observed temperature profiles using the surface roughness model (Shimaki et al., 2020). It estimates the thermophysical properties of the surface to reveal the evolutional history of Ryugu. The observed data have been published on the web page of PDS/NASA and DATRS/JAXA. The observed raw images (Level-1) and the observed brightness temperature images (Level-2) are currently available. In this study, we made the temperature projection maps onto the shape model of Ryugu using a geometric correction method (Arai et al., 2021). The projection method was ray projection from the shape model to a focal plane of TIR images. These observed images were fitted to the anticipated images calculated by the SPICE kernel using the Hayabusa2 attitude (CK) and body flame (FK). The resulting pointing accuracy was less than 10 m at the altitude of 10 km observations. The brightness temperature map on the shape model of Ryugu has been prepared for next publications as Level-3 products. The detailed map spatially resolved the temperature of shaded areas by large boulders. We found relatively hot areas caused by multiple radiations from the surroundings. The rotation axis of Ryugu is inclined about 8 degrees to the orbital plane. Therefore, it causes seasonal changes on the surface of Ryugu. Simulation results of solar radiation using the SPICE tool kit show that there are available in all-time sunlit or no sunlit areas on the polar regions of Ryugu. However, the effects of thermal radiations caused by the complex topography or boulders on the surface seem to reduce the seasonal changes of the surface temperature. For instance, TIR found hot spots in no sunlit areas of the polar region. In this presentation, we introduce the seasonal changes of the surface temperature using the Level-3 products and the temperature profile of the characteristic areas on Ryugu.