Kaula’s rule and its scaling law for the gravity fields of the Moon and the terrestrial planets

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  • 月惑星の重力場におけるカウラの法則とそのスケーリング則
  • ツキ ワクセイ ノ ジュウリョクバ ニ オケル カウラ ノ ホウソク ト ソノ スケーリングソク

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Abstract

Gravity fields of the Moon and terrestrial planets are modeled by combining spherical harmonics of various degrees/orders multiplied with the Stokes’ coefficients. These coefficients have been estimated for several celestial bodies including the Earth using tracking data of artificial satellites. The Kaula’s rule-of-thumb predicts that these coefficients are inversely proportional to the square of the degree n of the spherical harmonics. In this study, we confirmed that this is the case for the Moon, the Earth, Mars and Venus. A larger celestial body is hotter inside and has stronger surface gravity, resulting in smaller Stokes’ coefficients. Here we show that such coefficients obey a simple scaling law, i.e. they are inversely proportional to the square of the surface gravity of the body. The Moon has a strong dichotomy, i.e. the nearside has thin crust and flat terrain, whereas the farside has thick crust and rugged terrain. Here we also discuss how far such dichotomy may influence the scaling law.

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