[P-PS05] Lunar science and exploration

[PPS05-07] Scientific approaches to promotion of the lunar polar exploration

*Masahiro KAYAMA¹, Makiko Ohtake², Ko Hashizume³, Kazuto Saiki⁴, Chihiro Yamanaka⁴, Reiko Nomura⁵, Makoto Hareyama⁶, Yoshifumi Saito⁵, Teruaki Enoto⁷, Hideaki Miyamoto¹, Tomokatsu Morota¹, Yuzuru Karouji⁵, Yoshiaki Ishihara⁵, Hiroyasu Mizuno⁵, Takeshi Hoshino⁵, Dai ASOH⁵ (1.The University of Tokyo, 2.University of Aizu, 3.Ibaraki University, 4.Osaka University, 5.JAXA, 6.St. Marianna University, 7.RIKEN)

Keywords:Moon, Water, Mission, Lunar polar region, Water resource

The lunar polar exploration (LUPEX, a tentative name), planned by JAXA in collaboration with ISRO, is the robotic landing mission for water resource on a pole of the Moon. In the LUPEX mission scheduled to launch after 2023, the lander will touch down on the lunar polar region, the rover will deploy to travel on the surface, and various types of the attached instruments will measure the lunar materials to search for the water resource and to assess its quantity (the water content), quality (chemical composition of ice, whether it contains only H₂O or other species such as CO₂, CH₄, and H₂S), and usability (vertical and horizontal water distribution to check the accessibility). Lunar water is one of the most important resource in space because it is available for drinking water, breathing oxygen, hydrogen fuel, and building materials for lunar base, and is, therefore, absolutely essential for future manned space activity. Therefore, the attached instruments specialized in water analysis and some of them capable of collection of geological data on the Moon e.g., infrared spectroscopy named Advanced Lunar Imaging Spectrometer (ALIS), lunar thermogravimetric analyzer (LTGA), and aquatic detector using optical resonance (ADORE), were selected. There are, however, still less scientific data obtained from lunar samples or the simulant by experiments and simulations which reproduce ultra- to extreme high vacuum (10⁻⁷ to 10⁻¹⁰ Pa) and a very low temperature environment (<70 K to 390 K) of the lunar pole, in spite of dependence of the volatile properties (absorption, dehydration, and sublimation) on temperature and vacuum. Here, we introduce and review necessity of scientific approaches of collection of the basic data and establishment of the analytical method from the laboratory reproduction experiments and simulations to promote the LUPEX mission.

Lunar water is thought to be derivied from the following origins; solar wind, carbonaceous chondrite/comet collision, and degassing of magmatic eruption. Solar wind-originated hydrogen is implanted into the lunar surface materials and then a part of it changes into structural water via formation of the regolith agglutinate. Carbonaceous chondrite and comet collisions provide structural and hydrated water-bearing minerals such as serpentine and saponite into the Moon. They also theoretically cause formation of evaporate layer of their volatile constituents, supplying various gas (for example, H₂O, CO₂, and CH₄) with the lunar surface. Volatiles of H, C, Cl, F, S and their molecular species are likely to be released by degassing of magmatic eruption from the lunar interior into the surface. Thus, these processes supply various types of volatiles with the Moon, especially the poles under the very low-temperature environment that facilitate migration and deposit of volatiles. Therefore, the attached instruments with the rover of LUPEX should allow in-situ analyses of volatile with wide variety of atomic and molecular species and each of the contents with adequate accuracy and reliability, based on the basic data and the analytical method from the reproduction experiments. In the presentation, we will mention the scientific approaches of the laboratory reproduction experiment for the sake of this achievement, e.g., IR, Thermogravimetric analysis and Thermal Desorption Spectroscopy measurements of the lunar samples and the simulant with various types of structural, hydrate, and adsorbed volatiles to reveal characteristics of volatile signals from the instruments and to clarify absorption, dehydration, and sublimation temperature under the reproduction environment of ultra- to extreme high vacuum and a very low temperature. The results achieved can be also useful for calibration curve of volatile signals from the instruments, selection of standard materials for water analysis and assessment of the attached instrument performance (spatial resolution, detection limit, and temperature rate and limit).