Japan Geoscience Union Meeting 2015

Presentation information


Symbol P (Space and Planetary Sciences) » P-PS Planetary Sciences

[P-PS23] Lunar science and exploration

Tue. May 26, 2015 9:00 AM - 10:45 AM A02 (APA HOTEL&RESORT TOKYO BAY MAKUHARI)

Convener:*Hiroshi Nagaoka(Waseda Univ.), Tomokatsu Morota(Graduate School of Environmental Studies, Nagoya University), Masaki N Nishino(Solar-Terrestrial Environment Laboratory, Nagoya University), Chikatoshi Honda(The University of Aizu), Yuichiro Cho(Department of Physics, Rikkyo University), Chair:Makiko Ohtake(宇宙航空研究開発機構 宇宙科学研究本部 固体惑星科学研究系), Yoshiko Ogawa(The University of Aizu)

9:15 AM - 9:30 AM

[PPS23-14] Flow patterns in spherical mantles with small size of core; the effect of temperature dependent viscosity

*Takatoshi YANAGISAWA1, Masaki OGAWA2, Masanori KAMEYAMA3 (1.Japan Agency for Marine-Earth Science and Technology, 2.Graduate School of Arts and Sciences, Univ. of Tokyo, 3.Geodynamic Research Center, Univ. of Ehime)

Keywords:Moon, 3D spherical shell, mantle convection, size of the core, flow pattern

Clarifying the effects of three-dimensional spherical geometry on mantle convection is a major issue of mantle dynamics in terrestrial planets. We study in detail the nature of thermal convection of a variable viscosity fluid in the basally heated spherical mantle of small planets with a small core, keeping in mind the application of our numerical models to the Moon. Spherical geometry affects mantle convection mildly when the ratio of the core-radius to the planetary radius rCMB takes an Earth-like value of 0.55, while it is thought to affect strongly when rCMB is small like Moon around 0.2. Here, we investigate the flow pattern systematically for rCMB from 0.1 to 0.6 with small to large viscosity dependence on temperature. We first estimate the critical Rayleigh number Rc for the onset of convective motion at various rCMB and the magnitude of temperature-dependence of viscosity by a linear perturbation analysis. Then, we study the convective flow pattern of thermal convection above Rc by numerical simulation. The result of our simulation is in good agreement with the linear analysis. The nature of convective flow pattern considerably changes as rCMB smaller than about 0.4. The flow pattern has smaller number of up- and down-wellings. We established regime diagrams of convection pattern in relation to the Rayleigh number and the temperature dependence of viscosity, for various value of rCMB. Stronger temperature dependence of viscosity is necessary for realizing the stagnant-lid regime of convection for smaller rCMB. It is due to the relatively smaller volume of high temperature region near the CMB. The horizontally averaged temperature at mid mantle remains low despite the strong temperature variation of viscosity when rCMB is small.