The latest advancements in exoplanet orbital evolution research by Associate Professor Wang Yue from the School of Astronautics of Beihang University have been published in The Astrophysical Journal Letters (ApJL), titled “Sculpting of Exoplanetary Systems Driven by a Misaligned Disk and Stellar Oblateness: Origin of Perpendicular Orbits in HD 3167.” Fu Tao, a doctoral student from the School of Astronautics, is the first author of the paper, with Associate Professor Wang Yue serving as the corresponding author.
In the research, the authors have identified a novel dynamical evolution mechanism explaining the origins of the orbital configuration of the exoplanetary system HD 3167. This mechanism has been demonstrated to play a key role in the early evolution of planetary systems.
Exoplanet science is a frontier topic in contemporary astronomy and space sciences. Since Michel Mayor and Didier Queloz discovered “51Pegasi b” in 1995, the first extrasolar planet orbiting a sun-like star, a lot of exoplanets have been discovered and confirmed, driving rapid development in this field. These exoplanets often exhibit unconventional orbital structures and configurations, challenging traditional planet formation and evolution theories related to the Solar System. The application of next-generation large telescopes has provided unprecedented opportunities for research in this area.
The HD 3167 system has attracted significant attention for its unique orbital characteristics, where its inner ultra-short-period planet exhibits perpendicular and retrograde orbits relative to its outer three planets (see Fig. 1). Existing theories can hardly account for its formation. Wang Yue’s research team investigate the role of disk-induced spin–orbit misalignments in shaping the architecture of multiplanet systems, taking into account the combined effect of the host star's oblateness and the full-space disk potential. They demonstrate that large mutual planetary inclinations can arise from a saddle-center bifurcation occurring during the photoevaporation of the disk. This bifurcation triggers an instant, nonadiabatic transition in the planet’s libration. Following this process, the orbital evolution diverges into several distinct patterns. In scenarios involving a near-polar primordial misalignment, the orbit, consistently librating about a coplanar equilibrium axis, can be captured by an orthogonal equilibrium during the decay of the stellar oblateness. However, the orbit will be eventually recaptured by the coplanar equilibrium, aligned or antialigned with the orientation of the outer orbit, resulting in either a prograde or retrograde inner-outer orbit configuration. Additionally, general relativity contributes to maintaining eccentricity stability within these dynamic scenarios.
Fig. 1: Schematic illustration of the dynamical history of the HD 3167 system (not to scale)
Through the proposed mechanism, the research provides a plausible explanation for the unique, near-perpendicular, and likely retrograde orbit architecture observed in the HD 3167 system, enhancing our understanding of exoplanetary system dynamics.
The Astrophysical Journal Letters is the premier journal for rapid publication of significant research in astronomy and astrophysics and isincluded in Nature Index.
This work has been supported by the National Natural Science Foundation of China and the Fundamental Research Funds for the Central Universities.
Original article link: https://iopscience.iop.org/article/10.3847/2041-8213/ad77d6
Editor: Tian Zimo, Lyu Xingyun
