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Constraints on the formation history and composition of Kepler planets from their distribution of orbital period ratios
Astronomy & Astrophysics ( IF 5.4 ) Pub Date : 2024-06-27 , DOI: 10.1051/0004-6361/202449371 Di-Chang Chen , Christoph Mordasini , Ji-Wei Xie , Ji-Lin Zhou , Alexandre Emsenhuber
Astronomy & Astrophysics ( IF 5.4 ) Pub Date : 2024-06-27 , DOI: 10.1051/0004-6361/202449371 Di-Chang Chen , Christoph Mordasini , Ji-Wei Xie , Ji-Lin Zhou , Alexandre Emsenhuber
Context. The Kepler high-precision planetary sample has revealed a ‘radius valley’ separating compact super-Earths from sub-Neptunes with lower densities. Super-Earths are generally assumed to be rocky planets that were probably born in situ, while the composition and formation of sub-Neptunes remains debated. Numerous statistical studies have explored planetary and stellar properties and their correlations to provide observational clues. However, no conclusive result on the origin of the radius valley or the composition of sub-Neptunes has been derived to date.Aims. To provide more constraints, our aim is to investigate the distributions of the orbital spacing of sub-Neptunes and super-Earth planets in Kepler systems and compare their distributions with theoretical predictions of planet pairs of different formation pathways and compositions in synthetic planetary systems.Methods. Based on the Kepler planetary sample, we derived the distributions of period ratios of sub-Neptune and super-Earth planet pairs. Using synthetic planetary systems generated by the Generation III Bern Model, we also obtained theoretical predictions of period ratio distributions of planet pairs of different compositions and origins.Results. We find that Kepler sub-Neptune pairs show a significant preference to be near first-order mean motion resonances by a factor of 1.7−0.3+0.3. This is smaller than the model predictions for ‘water-rich’ pairs but larger than that of ‘water-poor’ pairs by confidence levels of ~2σ. Kepler super-Earth pairs show no significant preference for mean motion resonances from a random distribution. The derived normalised fraction of near first-order resonances of actual Kepler super-Earth pairs is consistent with that of synthetic water-poor planet pairs but significantly (≳3σ) smaller than that of synthetic water-rich planet pairs.Conclusions. The orbital migration has been more important for sub-Neptunes than for super-Earths, suggesting a partial ex situ formation of the former and an origin of the radius valley caused in part by distinct formation pathways. However, the model comparisons also show that sub-Neptunes in Kepler multiple systems are not likely (~2σ) to all be water-rich planets born ex situ but a mixture of the two (in situ and ex situ) pathways. Whereas, Kepler super-Earth planets are predominantly composed of water-poor planets that were born inside the ice line, likely through a series of giant impacts without large-scale migration.
中文翻译：
轨道周期比分布对开普勒行星形成历史和组成的约束
语境。开普勒高精度行星样本揭示了一个“半径谷”，将致密的超级地球与密度较低的亚海王星分开。超级地球通常被认为是可能就地诞生的岩石行星，而亚海王星的组成和形成仍然存在争议。许多统计研究探索了行星和恒星的特性及其相关性，以提供观测线索。然而，迄今为止，尚未得出关于半径谷的起源或亚海王星的组成的结论性结果。为了提供更多约束，我们的目标是研究开普勒系统中的亚海王星和超级地球行星的轨道间距分布，并将其分布与合成行星系统中不同形成路径和组成的行星对的理论预测进行比较。 。基于开普勒行星样本，我们推导了亚海王星和超级地球行星对的周期比分布。利用第三代伯尔尼模型生成的合成行星系统，我们还获得了不同成分和起源的行星对周期比分布的理论预测结果。我们发现开普勒海王星对显示出显着偏好接近一阶平均运动共振 1.7 倍 −0.3+0.3. This is smaller than the model predictions for ‘water-rich’ pairs but larger than that of ‘water-poor’ pairs by confidence levels of ~2σ. Kepler super-Earth pairs show no significant preference for mean motion resonances from a random distribution. The derived normalised fraction of near first-order resonances of actual Kepler super-Earth pairs is consistent with that of synthetic water-poor planet pairs but significantly (≳3σ) smaller than that of synthetic water-rich planet pairs.Conclusions. The orbital migration has been more important for sub-Neptunes than for super-Earths, suggesting a partial ex situ formation of the former and an origin of the radius valley caused in part by distinct formation pathways. However, the model comparisons also show that sub-Neptunes in Kepler multiple systems are not likely (~2σ) to all be water-rich planets born ex situ but a mixture of the two (in situ and ex situ) pathways. Whereas, Kepler super-Earth planets are predominantly composed of water-poor planets that were born inside the ice line, likely through a series of giant impacts without large-scale migration.
更新日期：2024-06-27
中文翻译：
轨道周期比分布对开普勒行星形成历史和组成的约束
语境。开普勒高精度行星样本揭示了一个“半径谷”，将致密的超级地球与密度较低的亚海王星分开。超级地球通常被认为是可能就地诞生的岩石行星，而亚海王星的组成和形成仍然存在争议。许多统计研究探索了行星和恒星的特性及其相关性，以提供观测线索。然而，迄今为止，尚未得出关于半径谷的起源或亚海王星的组成的结论性结果。为了提供更多约束，我们的目标是研究开普勒系统中的亚海王星和超级地球行星的轨道间距分布，并将其分布与合成行星系统中不同形成路径和组成的行星对的理论预测进行比较。 。基于开普勒行星样本，我们推导了亚海王星和超级地球行星对的周期比分布。利用第三代伯尔尼模型生成的合成行星系统，我们还获得了不同成分和起源的行星对周期比分布的理论预测结果。我们发现开普勒海王星对显示出显着偏好接近一阶平均运动共振 1.7 倍 −0.3+0.3. This is smaller than the model predictions for ‘water-rich’ pairs but larger than that of ‘water-poor’ pairs by confidence levels of ~2σ. Kepler super-Earth pairs show no significant preference for mean motion resonances from a random distribution. The derived normalised fraction of near first-order resonances of actual Kepler super-Earth pairs is consistent with that of synthetic water-poor planet pairs but significantly (≳3σ) smaller than that of synthetic water-rich planet pairs.Conclusions. The orbital migration has been more important for sub-Neptunes than for super-Earths, suggesting a partial ex situ formation of the former and an origin of the radius valley caused in part by distinct formation pathways. However, the model comparisons also show that sub-Neptunes in Kepler multiple systems are not likely (~2σ) to all be water-rich planets born ex situ but a mixture of the two (in situ and ex situ) pathways. Whereas, Kepler super-Earth planets are predominantly composed of water-poor planets that were born inside the ice line, likely through a series of giant impacts without large-scale migration.
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