[P-PS06] 月の科学と探査

[PPS06-16] Dielectric constant of lunar simulants at the THz band for the future lunar mission

*小林 真輝人¹、山田 崇貴³、Wang Suyun³、笠井 康子³、宮本 英昭^2,1 (1.東京大学理学系研究科地球惑星科学専攻、2.東京大学工学系研究科システム創成学専攻、3.情報通信研究機構)

キーワード：月、テラヘルツ波、誘電率

Lunar Terahertz SUrveyor for KIlometer-scale MappIng (TSUKIMI) is a new mission concept to map the very-shallow subsurface of the moon by measuring lunar brightness temperature in the THz band, thus facilitating the understanding of the emission from the lunar regolith. The emissivity is primarily controlled by the material’s dielectric constant, which holds valuable information for identifying lunar resources, including putative water ice. However, deciphering from the measured data to the lunar bulk composition is challenging because the dielectric constant of materials is a function of several parameters whose dependencies are not fully understood. The sensitivities of the temperature and the water-ice content in the lunar regolith would be the most crucial factors for detecting putative water ice. Thus, we are preparing a systematic measurement of the dielectric constant of various lunar regolith simulants. To design the system of laboratory measurements, we theoretically calculate the dielectric constant at the THz band by using the Debye model, which is one of the most reliable models to estimate the dielectric constant of materials. Combining the results at the UHF-SHF band, we find that the temperature dependence, which is among the most important factors controlling the dielectric constant at the UHF-SHF band, could generally be negligible in the THz band. In addition, we confirm that the difference between the dielectric constant of the regolith and water-ice could become larger at the THz band than the UHF-SHF band. Thus, the existence of the water-ice is more sensitive to the bulk dielectric constant at the THz band, implying that the passive observation at the THz band has a significant advantage in determining the water-ice in the very-shallow lunar subsurface.