Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Heidelberg, Germany.
School of Physics and Astronomy, University of Leicester, Leicester, UK.
Nature. 2020 Oct;586(7830):528-532. doi: 10.1038/s41586-020-2800-0. Epub 2020 Oct 21.
Planet formation is generally described in terms of a system containing the host star and a protoplanetary disk, of which the internal properties (for example, mass and metallicity) determine the properties of the resulting planetary system. However, (proto)planetary systems are predicted and observed to be affected by the spatially clustered stellar formation environment, through either dynamical star-star interactions or external photoevaporation by nearby massive stars. It is challenging to quantify how the architecture of planetary sysems is affected by these environmental processes, because stellar groups spatially disperse within less than a billion years, well below the ages of most known exoplanets. Here we identify old, co-moving stellar groups around exoplanet host stars in the astrometric data from the Gaia satellite and demonstrate that the architecture of planetary systems exhibits a strong dependence on local stellar clustering in position-velocity phase space. After controlling for host stellar age, mass, metallicity and distance from the star, we obtain highly significant differences (with p values of 10 to 10) in planetary system properties between phase space overdensities (composed of a greater number of co-moving stars than unstructured space) and the field. The median semi-major axis and orbital period of planets in phase space overdensities are 0.087 astronomical units and 9.6 days, respectively, compared to 0.81 astronomical units and 154 days, respectively, for planets around field stars. 'Hot Jupiters' (massive, short-period exoplanets) predominantly exist in stellar phase space overdensities, strongly suggesting that their extreme orbits originate from environmental perturbations rather than internal migration or planet-planet scattering. Our findings reveal that stellar clustering is a key factor setting the architectures of planetary systems.
行星形成通常用包含主星和原行星盘的系统来描述，其中内部特性（例如质量和金属丰度）决定了最终行星系统的特性。然而，（原）行星系统被预测和观测到受到恒星形成环境中空间聚集的影响，这种影响通过恒星之间的动力学相互作用或附近大质量恒星的外部光蒸发来实现。量化行星系统的结构如何受到这些环境过程的影响具有挑战性，因为恒星群在不到 10 亿年的时间内就会在空间上分散，远低于大多数已知系外行星的年龄。在这里，我们在 Gaia 卫星的天体测量数据中识别出围绕系外行星宿主恒星的古老共动恒星群，并证明行星系统的结构在位置-速度相空间中强烈依赖于局部恒星聚集。在控制了宿主恒星的年龄、质量、金属丰度和与恒星的距离后，我们在行星系统特性方面获得了高度显著的差异（p 值为 10 到 10），即在相空间过密度（由比无结构空间更多的共动恒星组成）和场之间。相空间过密度中行星的半长轴和轨道周期的中位数分别为 0.087 天文单位和 9.6 天，而场中恒星周围行星的半长轴和轨道周期中位数分别为 0.81 天文单位和 154 天。“热木星”（质量大、短周期的系外行星）主要存在于恒星相空间过密度中，这强烈表明它们极端的轨道起源于环境扰动，而不是内部迁移或行星-行星散射。我们的发现表明，恒星聚集是设定行星系统结构的关键因素。
