10:15 AM - 10:30 AM
[MIS25-06] What should be observed on the vertical wall of a hole in Mare Tranquillitatis?
★Invited Papers
Keywords:Mare Tranquilltatis, hole, shield volcano, regolith
In 2009, SELENE discovered a large vertical hole in Mare Tranquillitatis (MTH) by Terrain Camera (TC) with resolution of 10 m/pixel. Haruyama et al. (2009) hypothesized that it is a possible “skylight” of a lava tube. The United States Lunar Reconnaissance Orbiter (LRO) later re-measured/ re-estimated by images of Narrow Angle Camera (NAC) with resolution of 0.5 to 2 m/pixel. The results of observation are as follows. MTH is 100×105 m in diameter and 105 m in depth. The vertical wall of the hole exhibits layered structures. Conclusive evidence that large space is opening around the floor of MTH. The volcanism on the Moon has been understood to dominate extrusion of flood basalts from fissures. However, recently, it has become clear that shield volcanoes play an important role of mare volcanism. Many small shield volcanoes have been found in the vicinity of MTH (Spudis et al., 2013, Head et al., 2021). Japanese scientists and engineers formed a research group to explore lunar and planetary caverns. They named the project UZUME, after a goddess appearing in "Kojiki" and "Nihon Shoki" which are the oldest historical documents in Japan. The UZUME research group is proposing landing into MTH directly, performing observation at the wall and floor of the hole. There is no water and wind erosion, and very little structural movement on the Moon. Therefore, there are very few outcrops that can apply the interpretive framework of cross-sectional geology. MTH is the best and largest natural outcrop on the Moon. I propose that the layers exposed at the wall of MTH will be observed by a small camera. It will obtain data on the thickness and the morphology of the lava layers and paleoregolith layers. The important observation items are as follows. 1) Examining whether the lava layers were emplaced as thin but numerous complex flows or thick inflated flows. 2) Measuring the thickness of lava layers and determining whether they come from one source or multiple sources. 3) Measuring of the thickness of paleoregolith layers. Paleoregolith layers are important to estimate any hiatuses between lava flows. Greater than one centimeter of paleoregolith would suggest several million years of hiatus. These data will be great help to understand the style, flux, and timescale of volcanism on the Moon.