Sample studies and SELENE (Kaguya) observations of purest anorthosite (PAN) in the primordial lunar crust for future sample return mission

1Hiroshi Nagaoka,2Makiko Ohtake,3Yuzuru Karouji,4Masahiro Kayama,3Yoshiaki Ishihara5 Satoru Yamamoto,6Risa Sakai
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115370]
1Cluster for Pioneering Research, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
2The University of Aizu, Ikki Machi, Tsuruga, Aizu Wakamatsu City 965-8580, Japan
3JAXA Space Exploration Center, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara 252-5210, Japan
4Department of General Systems Studies, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
5Geological Survey of Japan (GSJ), National Institute of Advanced Industrial Science and Technology (AIST), Central 7, Higashi 1-1-1, Tsukuba 305-8567, Japan
6Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan
Copyright Elsevier

Purest anorthosite (PAN), which consists mostly of plagioclase (≥98%), provides key information for understanding the deep crust of the Moon, because PAN observed at central peaks of large impact craters was uplifted from a deep-seated layer. For future sample return of PAN, we examined the visible and near-infrared spectra of lunar meteorites and the mineralogical and petrological studies for Apollo FAN 60015. Sample analyses for lunar meteorites and Apollo FAN 60015 showed the existence of PAN in lunar samples. However, PAN clasts in lunar meteorites were so small that not enough sampled material could be secured for multiple analyses, such as determining their crystallization ages. The lunar meteorites were also heavily brecciated by multiple impacts on the surface. The brecciation and recrystallization on the surface may have disturbed the original information (i.e., age, texture, etc). Therefore, sample return of PAN rocks that have recently fallen from the central peaks of the large craters is required for analysis to determine the parent magma composition and timing of PAN formation. We investigated the PAN distributions in Jackson crater on the lunar farside and found that PAN rocks are widely distributed over the central peak and parts of the crater wall, using SELENE (Kaguya) observational data to locate where PAN would best be collected from the lunar surface. Based on the slope that a rover can manage, we recommend two areas appropriate for collecting samples of PAN rocks that have separated from the central peak.

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