New Insights on Planet Formation in WASP-47 from a Simultaneous Analysis of Radial Velocities and Transit Timing Variations
New Insights on Planet Formation in WASP-47 from a Simultaneous Analysis of Radial Velocities and Transit Timing Variations
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通过同时分析径向速度和凌日时间变化对 WASP-47 中行星形成的新见解
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发表时间：
2017
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通讯作者：
B. Benneke
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作者：
L. Weiss;K. Deck;E. Sinukoff;E. Petigura;E. Agol;Eve J. Lee;J. Becker;A. Howard;H. Isaacson;I. Crossfield;B. Fulton;L. Hirsch;B. Benneke
测量单个行星系统中精确的行星质量、密度和轨道动力学是了解行星形成的重要途径。 WASP-47 系统具有不寻常的架构，激发了复杂的形成理论。该系统包括一颗热木星（“b”），邻近内部（“e”）和外部（“d”）亚海王星，以及一颗长周期偏心巨行星（“c”）。我们同时对开普勒 K2 任务的凌日时间和 118 个径向速度进行建模，以确定 WASP-47 行星的精确质量、密度和开普勒轨道要素。与仅使用 RV ( ) 或 TTV ( ) 获得的结果相比，结合 RV 和 TTV 可以更好地估计行星 d ( ) 的质量。行星 e 和 d 的密度较高，这与在挥发性较差的环境中光蒸发和/或形成的历史一致。通过我们的RV和TTV分析，我们发现行星轨道具有与太阳系行星相似的偏心率。 WASP-47 系统与我们的太阳系有三个相似之处：(1) 行星轨道接近圆形且共面，(2) 行星没有陷入平均运动共振，(3) 行星具有不同的成分。目前的单过程系外行星形成理论都没有充分重现 WASP-47 系统（或我们的太阳系）的这三个特征。我们认为WASP-47就像太阳系一样，分两个阶段形成：首先，巨行星在富含气体的盘中形成并迁移到目前的位置，其次，高密度的亚海王星在缺乏气体的环境中就地形成。
Measuring precise planet masses, densities, and orbital dynamics in individual planetary systems is an important pathway toward understanding planet formation. The WASP-47 system has an unusual architecture that motivates a complex formation theory. The system includes a hot Jupiter (“b”) neighbored by interior (“e”) and exterior (“d”) sub-Neptunes, and a long-period eccentric giant planet (“c”). We simultaneously modeled transit times from the Kepler K2 mission and 118 radial velocities to determine the precise masses, densities, and Keplerian orbital elements of the WASP-47 planets. Combining RVs and TTVs provides a better estimate of the mass of planet d ( ) than that obtained with only RVs ( ) or TTVs ( ). Planets e and d have high densities for their size, consistent with a history of photoevaporation and/or formation in a volatile-poor environment. Through our RV and TTV analysis, we find that the planetary orbits have eccentricities similar to the solar system planets. The WASP-47 system has three similarities to our own solar system: (1) the planetary orbits are nearly circular and coplanar, (2) the planets are not trapped in mean motion resonances, and (3) the planets have diverse compositions. None of the current single-process exoplanet formation theories adequately reproduce these three characteristics of the WASP-47 system (or our solar system). We propose that WASP-47, like the solar system, formed in two stages: first, the giant planets formed in a gas-rich disk and migrated to their present locations, and second, the high-density sub-Neptunes formed in situ in a gas-poor environment.