Updated Compositional Models of the TRAPPIST-1 Planets
Updated Compositional Models of the TRAPPIST-1 Planets
复制标题
TRAPPIST-1 行星的更新组成模型
DOI：
10.3847/2515-5172/aacf43
复制
发表时间：
2018
期刊：
影响因子：
--
通讯作者：
S. Desch
中科院分区：
文献类型：
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作者：
C. Unterborn;N. Hinkel;S. Desch
在Unterborn et al.（2018）发表了TRAPPIST-1系统的初始质量-半径-组成模型后，在Grimm et al.（2018）中更新了行星质量。我们最初采用Wang et al.， 2017的数据集，他们报告的密度与更新后的值不同。观测到的密度差异改变了推断出的行星挥发物含量。Grimm等人（2018）报告称，TRAPPIST-1 b、d、f、g和h与<5 wt%的水相一致，TRAPPIST-1 c和e的内部大部分是岩石。在这里，我们提供了更新的结果，使用Grimm等人，2018年的质量重新计算了水的馏分和潜在的替代成分。总的来说，只有当行星的核心很小（< 23% wt%）时，我们才能重现Grimm等人2018年关于行星b、d和g含水量很小的结果。我们表明，如果这些行星的核心与地球大致大小（33% wt%），那么高达40% wt%的显著水含量是可能的。我们发现行星c、e、f和h的挥发包层在0-35 wt%之间，这也与完全氧化和完全缺乏铁核是一致的。我们在这里注意到，纯MgSiO$_3$行星（Fe/Mg = 0）并不是确定含有挥发物的行星概率的真正的最低密度端元质量半径曲线。所有的岩石行星都可能含有一些铁，要么在地核中，要么在地幔中被氧化。我们认为，对于氧化系统来说，真正的低密度端元应该是具有最低合理Fe/Mg和完全无核的行星。使用这种逻辑，我们断言行星b、d和g可能必须具有显著的挥发层，因为端元行星模型产生的质量太高，即使考虑到质量和半径的不确定性。
After publication of our initial mass-radius-composition models for the TRAPPIST-1 system in Unterborn et al. (2018), the planet masses were updated in Grimm et al. (2018). We had originally adopted the data set of Wang et al., 2017 who reported different densities than the updated values. The differences in observed density change the inferred volatile content of the planets. Grimm et al. (2018) report TRAPPIST-1 b, d, f, g, and h as being consistent with <5 wt% water and TRAPPIST-1 c and e has having largely rocky interiors. Here, we present updated results recalculating water fractions and potential alternative compositions using the Grimm et al., 2018 masses. Overall, we can only reproduce the results of Grimm et al., 2018 of planets b, d and g having small water contents if the cores of these planets are small (<23 wt%). We show that, if the cores for these planets are roughly Earth-sized (33 wt%), significant water fractions up to 40 wt% are possible. We show planets c, e, f, and h can have volatile envelopes between 0-35 wt% that are also consistent with being totally oxidized and lacking an Fe-core entirely. We note here that a pure MgSiO$_3$ planet (Fe/Mg = 0) is not the true lowest density end-member mass-radius curve for determining the probability of a planet containing volatiles. All planets that are rocky likely contain some Fe, either within the core or oxidized in the mantle. We argue the true low density end-member for oxidizing systems is instead a planet with the lowest reasonable Fe/Mg and completely core-less. Using this logic, we assert that planets b, d and g likely must have significant volatile layers because the end-member planet models produce masses too high even when uncertainties in both mass and radius are taken into account.