Three-dimensional simulations of the lunar sodium exosphere and its tail

• Published in: Journal of Geophysical Research: Space Physics Vol. 116; no. A7
• Main Authors: Lee, Dong-Wook, Kim, Sang J., Lee, Dong-Hun, Jin, Ho, Kim, Kap-Sung
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01.07.2011
• Subjects: Atmosphere; Atmospheric sciences; Auroras; exosphere; Ionization; Monte Carlo; Monte Carlo simulation; Moon; Planets; simulations; Sodium; Solar radiation; tail; Velocity; Velocity distribution
• ISSN: 0148-0227; 2169-9380; 2156-2202; 2169-9402
• DOI: 10.1029/2011JA016451

The brightness distributions of the lunar sodium exosphere reported by Flynn and Mendillo (1993) and the receding velocities of the lunar sodium tail observed by Mierkiewicz et al. (2006) are reproduced by 3‐D Monte Carlo simulations. We consider the effects of two spatially different sodium sources simultaneously: dayside source with the dependency of solar zenith angle and an isotropic source due to micrometeoroid impact. In the simulations, the following effects are taken into account: (1) the gravity of the Moon, the Earth, and the Sun with the orbital motion of the Moon; (2) photoionizations, solar radiation pressure, and returns to the lunar surface; and (3) the shadows of the Earth and Moon. The sodium brightness observed by Flynn and Mendillo (1993) is successfully modeled, from which the most probable source ratio between the isotropic and dayside sources is estimated to be 70%∼80%: 30%∼20%, respectively. The best coma model provides an initial velocity of 2.0 km/s with a narrow Doppler width of 0.2 km/s and a total production rate of 0.7 × 1022/s. On the basis of the best 3‐D lunar coma model, we also simulate the receding velocity distribution of lunar sodium tail, and we find satisfactory models for high receding velocity and its wide dispersion observed by Mierkiewicz et al. (2006) considering the effect of variable solar radiation pressure and appropriate ionization times. Key Points 3‐D simulations for lunar sodium exosphere Reproduction of lunar sodium brightness near the Moon Reproduction of sodium brightness and velocity distribution at tail