[P-PS06] Lunar Science and Exploration

[PPS06-P20] Estimation of light environments in a lunar Hole and a subsurface cavern by simulation of reflection

*Kodai Ikeya¹, Junichi Haruyama², Wataru Miyake¹, Makoto Tanaka¹ (1.Tokai University, 2.JAXA)

Keywords:Moon, Lunar Hole, simulation of reflection

Luner vertical holes were discovered in the image data observed by the Terrain Camera onboard the lunar orbiter SELENE (nicknamed as KAGUYA). From the slant angle observations of the Lunar Reconnaissance Orbiter (LRO), it has been found that spaces are horizontally expanding at the bottom of the holes. The holes are thought to be skylights of subsurface caverns such as lava tubes. Exploration of lunar subsurface caverns below vertical holes is expected to provide not only information for utilization of the holes and caverns, but also that for understanding the formation mechanism of vertical holes and the history of lunar volcanism. In order to understand the structure and physical properties of holes and subsurface caverns, image data for them are important. However, there has not had studied for light environments of the holes and associated caverns. In this study, therefore, we modeled a lunar hole and obtained the irradiance and radiance in the hole by numerical simulation to estimate the light environments in a hole and a cavern which is expanding from the bottom of the hole. As a model, we used a cylindrical model for the vertical hole with a radius and a wall height of 50 m, and a height of the cavern of 50 m. We assume an isotropic diffuse reflection with albedo of a parameter R for the surface of the hole and cavern. A numerical simulation result for this model showed that at noon, when the sun is at the zenith of the hole, the ceiling and walls of the cavern within 100 m from the center of the hole are illuminated by reflected light from the entire bottom of the hole, giving a maximum value of the irradiance is of about 50 × R % of the solar irradiance. In the same configuration model, when the solar altitude is 45 degrees, a case of no direct solar radiation enters insertion onto the bottom of the hole, the bottom is illuminated by reflected light from the walls, giving irradiance value of about 1 to 7 × R % of the solar irradiance.