Mass-Radius Relationships for Solid Exoplanets
Mass-Radius Relationships for Solid Exoplanets
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DOI：
10.1086/521346
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发表时间：
2007-07
期刊：
影响因子：
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通讯作者：
S. Seager;S. Seager;M. Kuchner;C. Hier-Majumder;B. Militzer
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文献类型：
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作者：
S. Seager;S. Seager;M. Kuchner;C. Hier-Majumder;B. Militzer
我们使用新的冷行星内部模型来研究固体系外行星的质量-半径关系，考虑主要由铁，硅酸盐，水和碳化合物组成的行星。我们发现，我们考虑的所有组成的冷类地行星的质量-半径关系遵循一个通用的函数形式，而不是一个简单的幂律：log 10 Rs = k1 + log 10（Ms）-k2 M，直到Mp = 20 M，其中Ms和Rs是标度的质量和半径值。这种函数形式的出现是因为固体行星的常见组成部分都有状态方程，这些状态方程可以很好地近似为形式ρ = ρ0 + cPn的修正多面体。我们发现，非常详细的行星内部模型，包括温度结构和相变，是没有必要的固体系外行星的质量和半径测量散装组成。对于没有实质性大气层的固态系外行星，我们也发现了以下几点：行星质量和半径的不确定性分数为5%时，可以区分主要由铁或硅酸盐或水冰组成的行星，但不能区分更详细的成分;不确定性分数为5%时，可以确定水质量为25%的水冰行星;对于一个给定的质量来说，最小的行星尺寸是一个纯铁行星;碳行星的质量-半径关系与硅酸盐和水行星的质量-半径关系重叠，因为它们具有相似的零压密度和状态方程。我们提出了“超级地球”的定义，该定义基于具有大量气体包层的行星和不具有气体包层的行星之间半径的明显差异。
We use new interior models of cold planets to investigate the mass-radius relationships of solid exoplanets, considering planets made primarily of iron, silicates, water, and carbon compounds. We find that the mass-radius relationships for cold terrestrial mass planets of all compositions we considered follow a generic functional form that is not a simple power law: log10 Rs = k1 + log10(Ms) - k2M for up to Mp ≈ 20 M⊕, where Ms and Rs are scaled mass and radius values. This functional form arises because the common building blocks of solid planets all have equations of state that are well approximated by a modified polytrope of the form ρ = ρ0 + cPn. We find that highly detailed planet interior models, including temperature structure and phase changes, are not necessary to derive solid exoplanet bulk composition from mass and radius measurements. For solid exoplanets with no substantial atmosphere we have also found the following: with 5% fractional uncertainty in planet mass and radius it is possible to distinguish among planets composed predominantly of iron or silicates or water ice but not more detailed compositions; with ~5% uncertainty water ice planets with ≳25% water by mass may be identified; the minimum plausible planet size for a given mass is that of a pure iron planet; and carbon planet mass-radius relationships overlap with those of silicate and water planets due to similar zero-pressure densities and equations of state. We propose a definition of "super-Earths" based on the clear distinction in radii between planets with significant gas envelopes and those without.