A General Origin for Multi-Planetary Systems With Significantly Misaligned USP Planets

Abstract

Ultra-short period (USP) planets are exoplanets which have orbital periods of less than one day and are unique because they orbit inside the nominal magnetic truncation gap of their host stars. In some cases, USP planets have also been observed to exhibit unique dynamical parameters such as significant misalignments in inclination angle with respect to nearby planets. In this paper, we explore how the geometry of a multi-planet system hosting a USP planet can be expected to evolve as a star ages. In particular, we explore the relationship between the mutual inclination of the USP planet and the quadrupole moment ($J_2$) of the host star. We use secular perturbation theory to predict the past evolution of the example TOI-125 system, and then confirm the validity of our results using long-term N-body simulations. Through investigating how the misalignment between the candidate USP planet and the three other short-period planets in the TOI-125 system arose, we intend to derive a better understanding of the population of systems with misaligned USP planets and how their observed parameters can be explained in the context of their dynamical histories.

Accepted to AJ

References in corpus (16)

• A Study of the Shortest-Period Planets Found With Kepler
• Kepler Multi-Planet Systems Exhibit Unexpected Intra-system Uniformity in Mass and Radius
• AMD-stability and the classification of planetary systems
• A Dynamical Analysis of the Kepler-80 System of Five Transiting Planets
• Kepler-445, Kepler-446 and the Occurrence of Compact Multiples Orbiting Mid-M Dwarf Stars
• On the Dynamical Stability of the Solar System
• Early Excitation of Spin-Orbit Misalignments in Close-in Planetary Systems
• Spin-orbit Misalignment as a Driver of the Kepler Dichotomy
• Are Inner Disc Misalignments Common? ALMA Reveals an Isotropic Outer Disc Inclination Distribution for Young Dipper Stars
• Formation of Ultra-Short-Period Planets by Obliquity-Driven Tidal Runaway
• Mass determinations of the three mini-Neptunes transiting TOI-125
• The Origin of Systems of Tightly Packed Inner Planets with Misaligned, Ultra-Short-Period Companions
• Mutual Inclination Excitation by Stellar Oblateness
• Stellar Oblateness versus Distant Giants in Exciting Kepler Planet Mutual Inclinations
• Migrating Planets into Ultra-Short-Period Orbits during Episodic Accretion Events
• The distribution of mutual inclinations arising from the stellar quadrupole moment