Abstract
Contribution of Tidal Heating to Thermal History of the Moon
Y. Morisawa (University of Tokyo, ISAS), H. Mizutani (ISAS)
1. Introduction
The Moon was much closer to the Earth in the past than at present. The distance of the Moon from the Earth is about 60Re (Re = Earth radius) at present, and was about 3Re in the past. Therefore, the early lunar thermal state is thought to be strongly affected by the tidal dissipation.
2. Purpose
The possible contributions of tidal heating to lunar thermal history are investigated by Peale and Cassen (1978). But Peale and Cassen calculated the tidal heating taking into account the orbital evolution and concluded that tidal contributions to lunar thermal history were probably not important, so lunar thermal history was essentially controlled by radiogenic sources and initial accretional heating. The purpose of the present study is to reexamine the Peale and Cassen's conclusion from a view point that the tidal dissipation is significantly affected by the orbital evolution and internal structure of the Moon.
3. Calculation
We calculate the lunar thermal history, taking into account the orbital evolution and the possible internal structures of the early Moon. The procedure of calculation is on the basis of Peale and Cassen et al. (1978) and Kawakami and Mizutani et al. (1986).
4. Conclusion
The calculation results indicates that the tidal dissipation may be an important source of the heat energy and that the thermal history and orbital evolution must be coupled in order to better understand the early thermal history. But there exist several uncertain parameters for example dissipation factor Q and eccentricity, so we discussed the dependence of lunar thermal evolution on the uncertain parameters.
[Reference]
[1]Peale, S., and P. Cassen. Contribution of Tidal Dissipation to Lunar Thermal History. Icarus 36, 245-269 (1978).
[2] Kawakami,S., and H. Mizutani. Thermal history of IO. Icarus 70, 78-98 (1986).
