Biddle Lauren I, Bowler Brendan P, Morgan Marvin, Tran Quang H, Wu Ya-Lin
Department of Astronomy, The University of Texas at Austin, Austin, TX, USA.
Department of Physics, University of California, Santa Barbara, Santa Barbara, CA, USA.
Nature. 2025 Aug;644(8076):356-361. doi: 10.1038/s41586-025-09324-0. Epub 2025 Aug 6.
Exoplanets are organized in a broad array of orbital configurations that reflect their formation along with billions of years of dynamical processing through gravitational interactions. This history is encoded in the angular momentum architecture of planetary systems-the relation between the rotational properties of the central star and the orbital geometry of planets. A primary observable is the alignment (or misalignment) between the rotational axis of the star and the orbital plane of its planets, known as stellar obliquity. Hundreds of spin-orbit constraints have been measured for giant planets close to their host stars, many of which have revealed planets on misaligned orbits. A leading question that has emerged is whether stellar obliquity originates primarily from gravitational interactions with other planets or distant stars in the same system, or if it is 'primordial'-imprinted during the star-formation process. Here we present a comprehensive assessment of primordial obliquities between the spin axes of young, isolated Sun-like stars and the orientation of the outer regions of their protoplanetary disks. Most systems are consistent with angular momentum alignment but about one-third of isolated young systems exhibit primordial misalignment. This suggests that some obliquities identified in planetary systems at older ages-including the Sun's modest misalignment with planets in the Solar System-could originate from initial conditions of their formation.
系外行星的轨道构型多种多样，这反映了它们的形成过程以及数十亿年来通过引力相互作用进行的动力学演化。这段历史被编码在行星系统的角动量结构中，即中央恒星的自转特性与行星轨道几何形状之间的关系。一个主要的可观测指标是恒星自转轴与其行星轨道平面之间的对齐（或不对齐）情况，即恒星倾角。对于靠近其主恒星的巨行星，已经测量了数百个自旋 - 轨道约束条件，其中许多都揭示了轨道不对齐的行星。由此出现的一个主要问题是，恒星倾角主要是源于与同一系统中其他行星或遥远恒星的引力相互作用，还是在恒星形成过程中就被“初始设定”的。在这里，我们对年轻、孤立的类太阳恒星自转轴与其原行星盘外部区域方向之间的初始倾角进行了全面评估。大多数系统与角动量对齐一致，但约三分之一的孤立年轻系统表现出初始不对齐。这表明在较老年龄的行星系统中确定的一些倾角，包括太阳与太阳系行星的适度不对齐，可能源于它们形成的初始条件。
