[P-PS09] Lunar Science and Exploration

[PPS09-03] Description of the boulders around SLIM's landing site

*Chikatoshi Honda¹, Hiroyuki Sato³, Yasuhiro Yokota³, Risa Miyazaki³, Iori Kajitani³, Makiko Ohtake¹, Yusuke Nakauchi², Hiroshi Nagaoka², Kazuto Saiki², Masaki N Nishino³, Ryusuke Nishitani³, Yoshiaki Ishihara³, Shinichiro Sakai³ (1.The University of Aizu, 2.Ritsumeikan University, 3.Japan Aerospace Exploration Agency)

Keywords:Landing Site, Boulders, SLIM

On January 20, 2024 (JST), the SLIM spacecraft module landed on the eastern area of Shioli crater, a lunar surface rich in olivine. The area around Shioli crater is dominated by ejecta or rock masses that were scattered during the formation of Shioli crater, and is the final destination of this mission. Such rocks are expected to be olivine-rich rocks and were observed by the MBC. The landing site was carefully selected in advance because of the conflicting requirements of observation target and landing safely. The landing was almost completely controlled until the final stage of the landing operation based on images taken by the navigation camera (CAM). During the final stage, SLIM landed while moving to the east-southeast. However, the originally planned landing accuracy was achieved.
The scanned image of the area around the landing site observed by the Multiband Camera (MBC) from the landing site showed the presence of many boulders on the lunar surface. The MBC's autofocus function allows us to know the distance from the lens position to the object to be imaged. By using this function and the number of pixels per angle of view, we were able to determine the scale of the boulders to be observed. As a result, most of the boulders in the field of view had an apparent size of about 30 cm or less. The highest resolution image was taken by the Orbiter Hight Resolution Camera (OHRC) onboard Chandrayaan-2, which is taking images at this location. The OHRC's spatial resolution of 28 cm/px makes it difficult to locate the boulder observed by the MBC on the lunar orbiter image. We investigate the correspondence between boulders in MBC scan images and OHRC images and report preliminary results of boulder size-frequency distribution around the landing site.