On the Probability That a Rocky Planet’s Composition Reflects Its Host Star
On the Probability That a Rocky Planet’s Composition Reflects Its Host Star
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DOI：
10.3847/psj/abcaa8
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发表时间：
2020-11
影响因子：
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通讯作者：
J. Schulze;J. Wang 王;J. Johnson;B. Gaudi;C. Unterborn;W. R. Panero
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文献类型：
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作者：
J. Schulze;J. Wang 王;J. Johnson;B. Gaudi;C. Unterborn;W. R. Panero
行星的体积密度，以质量和半径来衡量，是行星结构和组成的结果。对于给定的密度，铁核、岩石地幔和气体包层的相对比例是简并的。这种简并减少了岩石行星没有显着的气体信封时，结构被假定为一个分化的铁芯和岩石地幔，其中核心质量分数（CMF）是一个一阶描述的行星的散装组成。岩石行星的CMF可以从体积密度和假设行星反映了主星星的主要岩石建造元素丰度（Fe，Mg和Si）来推导。对比CMF措施，因此，揭示了行星形成过程的结果多样性，包括地幔剥离，脱气，和/或后期挥发性交付。我们提出了一个统计上严格的分析，这两个CMF措施的一致性占行星质量和半径和宿主恒星化学丰度的观测不确定性。我们发现，这两个措施是不太可能被解析为统计上的差异，除非体积密度CMF是至少40%以上或50%以下的CMF推断从主机星星。开普勒-107 c有11颗可能的岩石系外行星，根据体积密度推断，其CMF明显大于其宿主星星的CMF（2σ），因此可能是一颗富含铁的超级水星。K2- 229 b，之前被描述为超级汞，但是，在1σ或2σ水平上不符合超级汞的阈值。
The bulk density of a planet, as measured by mass and radius, is a result of planet structure and composition. Relative proportions of iron core, rocky mantle, and gaseous envelopes are degenerate for a given density. This degeneracy is reduced for rocky planets without significant gaseous envelopes when the structure is assumed to be a differentiated iron core and rocky mantle, in which the core mass fraction (CMF) is a first-order description of a planet’s bulk composition. A rocky planet’s CMF may be derived both from bulk density and by assuming the planet reflects the host star’s major rock-building elemental abundances (Fe, Mg, and Si). Contrasting CMF measures, therefore, shed light on the outcome diversity of planet formation from processes including mantle stripping, out-gassing, and/or late-stage volatile delivery. We present a statistically rigorous analysis of the consistency of these two CMF measures accounting for observational uncertainties of planet mass and radius and host-star chemical abundances. We find that these two measures are unlikely to be resolvable as statistically different unless the bulk density CMF is at least 40% greater than or 50% less than the CMF as inferred from the host star. Applied to 11 probable rocky exoplanets, Kepler-107 c has a CMF as inferred from bulk density that is significantly greater than the inferred CMF from its host star (2σ) and is therefore likely an iron-enriched super-Mercury. K2-229b, previously described as a super-Mercury, however, does not meet the threshold for a super-Mercury at a 1σ or 2σ level.