[P-PS03] Rotation, inner dynamics and variations of natural processes on the Earth, the Moon and Mars.

★ [PPS03-02] 月核マントル境界直上の超低粘性領域内部の強い潮汐加熱

*原田 雄司¹、ホーセンス サンダー²、松本 晃治³、エン 建国⁴、平 勁松⁵、野田 寛大³、春山 純一⁶ (1.澳門科技大学太空科学研究所、2.メリーランド大学ボルチモア郡校宇宙科学技術研究探査センター、3.自然科学研究機構国立天文台、4.武漢大学測絵遥感信息工程国家重点実験室、5.中国科学院国家天文台、6.宇宙航空研究開発機構宇宙科学研究所)

キーワード：月, 核マントル境界, 低粘性領域, 潮汐加熱

Tidal heating due to viscous dissipation in a planetary body is an important energy conversion process, depending on its internal structure, and connected to its thermal and orbital states. Our moon is not an exception. Previous studies have calculated the tidal response including dependence of the dissipation on the lunar interior structure, but these studies did not completely explain the geodetically-observed dependence of the dissipation on the lunar tidal period. One possibility to interpret this frequency-dependence is a low-viscosity layer inside the mantle as a natural consequence of the strong seismic attenuation zone, because such a viscosity contrast affects this dependence. However, previous studies have not considered its potential impact. Here we show that the explicit influence of the low-viscosity zone successfully provides the frequency-dependent dissipation on the Moon consistent with the geodetic observables. We found that the above-mentioned high attenuation zone is equivalent to the low-viscosity layer. Furthermore, we also found that the resultant viscosity value is remarkably low, signifying a relaxation time close to the tidal period. This ultralow viscosity implies partial melting as formerly suggested. Our result demonstrates that the most effective dissipation is localised to this layer, indicating a blanket effect on the core. We anticipate that such tidal heating, balanced against convective cooling, maintains this layer over the course of the lunar tidal history.