Mutual Inclination Excitation by Stellar Oblateness

Abstract

Ultra-short-period planets (USPs) provide important clues to planetary formation and migration. Recently, it is found that the mutual inclinations of the planetary systems are larger if the inner orbits are closer ($\lesssim 5R_{\ast }$) and if the planetary period ratios are larger ($P_2/P_1\gtrsim 5$) (Dai et al. 2018). This suggests that the USPs experienced both inclination excitation and orbital shrinkage. Here we investigate the increase in the mutual inclination due to stellar oblateness. We find that the stellar oblateness (within $\sim 1$Gyr) is sufficient to enhance the mutual inclination to explain the observed signatures. This suggests that the USPs can migrate closer to the host star in a near coplanar configuration with their planetary companions (e.g., disk migration+tides or in-situ+tides), before mutual inclination gets excited due to stellar oblateness.

8 pages, 4 figures, 1 table; accepted for publication in ApJL

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Cited by in corpus (8)

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• Stellar Oblateness versus Distant Giants in Exciting Kepler Planet Mutual Inclinations
• Resonant and Ultra-short-period Planet Systems are at Opposite Ends of the Exoplanet Age Distribution
• Mutual Inclination of Ultra-Short-Period Planets with Time Varying Stellar J2-moment
• The distribution of mutual inclinations arising from the stellar quadrupole moment
• Planets Across Space and Time (PAST). VI. Age Dependence of the Occurrence and Architecture of Ultra-Short-Period Planet Systems
• Evidence for a Non-Dichotomous Solution to the Kepler Dichotomy: Mutual Inclinations of Kepler Planetary Systems from Transit Duration Variations
• General Relativity Can Prevent a Runaway Greenhouse on Potentially Habitable Planets Orbiting White Dwarfs