[P-PS04] Recent advances in the science of Venus

[PPS04-10] 金星の高い表面温度とマントル・ダイナミクス

*小河 正基

キーワード：金星、地表面温度、マントルダイナミクス

The surface temperature of Venus is as high as 750 K because of the strong greenhouse effect of its CO₂-rich atmosphere. I used a numerical model of magmatism in the convecting mantle to understand how this high surface temperature influences the mantle dynamics of Venus. The mantle evolves in two stages for the past 4 Gyrs, when the surface temperature is 750 K. On the earlier stage, a positive feedback between magmatism and mantle upwelling flow repeatedly causes episodes of volcanic activity (called “mantle burst”): a mantle upwelling flow generates magma by decompression melting, while the buoyancy of the generated magma reinforces the upwelling flow. Formation and recycling of the crust by this episodic magmatism is the dominant mechanism of mantle cooling on this stage. On the later stage, mantle burst subsides as the internal heat source of the mantle declines. Instead, a thermally driven mantle convection causes a more continuous and mild volcanic activity. When the surface temperature is reduced to 273 K, the lithosphere becomes stiffer because of the strong temperature-dependence of mantle viscosity to impede recycling of the crust by mantle burst on the earlier stage. Heat builds up more readily in the mantle, and mantle burst that is made less frequent owing to the stiffer lithosphere becomes more extensive. Even a magma ocean repeatedly develops in association with mantle burst on the earlier stage. The style and vigor of volcanic activity substantially depends on the surface temperature on Venus.