Evidence for a Nondichotomous Solution to the Kepler Dichotomy: Mutual Inclinations of Kepler Planetary Systems from Transit Duration Variations
Abstract
Early analyses of exoplanet statistics from the Kepler mission revealed that a model population of multiplanet systems with low mutual inclinations (~1°2°) adequately describes the multipletransiting systems but underpredicts the number of singletransiting systems. This socalled "Kepler dichotomy" signals the existence of a subpopulation of multiplanet systems possessing larger mutual inclinations. However, the details of these inclinations remain uncertain. In this work, we derive constraints on the intrinsic mutual inclination distribution by statistically exploiting transit duration variations (TDVs) of the Kepler planet population. When planetary orbits are mutually inclined, planetplanet interactions cause orbital precession, which can lead to detectable longterm changes in transit durations. These TDV signals are inclination sensitive and have been detected for roughly two dozen Kepler planets. We compare the properties of the Keplerobserved TDV detections to TDV detections of simulated planetary systems constructed from two population models with differing assumptions about the mutual inclination distribution. We find strong evidence for a continuous distribution of relatively low mutual inclinations that is well characterized by a powerlaw relationship between the median mutual inclination ( ${\tilde{\mu }}_{i,n}$ ) and the intrinsic multiplicity (n): ${\tilde{\mu }}_{i,n}={\tilde{\mu }}_{i,5}{(n/5)}^{\alpha }$ , where ${\tilde{\mu }}_{i,5}={1.10}_{0.11}^{+0.15}$ and $\alpha ={1.73}_{0.08}^{+0.09}$ . These results suggest that latestage planet assembly and possibly stellar oblateness are the dominant physical origins for the excitation of Kepler planet mutual inclinations.
 Publication:

The Astronomical Journal
 Pub Date:
 October 2021
 DOI:
 10.3847/15383881/ac0f7a
 arXiv:
 arXiv:2106.15589
 Bibcode:
 2021AJ....162..166M
 Keywords:

 Exoplanets;
 Exoplanet systems;
 Exoplanet catalogs;
 Exoplanet detection methods;
 Exoplanet dynamics;
 Transit duration variation method;
 Planetary system formation;
 Exoplanet formation;
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 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 Accepted to AJ, 19 pages, 10 figures (excluding appendix)