Kepler's Missing Planets

TL;DR

This study analyzes the distribution of orbital period ratios in Kepler multi-planet systems, revealing potential excesses near resonances that suggest dynamical interactions and the presence of missing planets affecting system architecture.

Contribution

It introduces a model comparing high and low multiplicity systems to identify potential missing planets and resonance effects in Kepler data.

Findings

Excess of planet pairs between 2:1 and 3:1 resonances in low multiplicity systems

Significant excess of planets near the 2:1 resonance in three-planet systems

Period ratio distributions can guide searches for missing planets

Abstract

We investigate the distributions of the orbital period ratios of adjacent planets in high multiplicity \kepler\ systems (four or more planets) and low multiplicity systems (two planets). Modeling the low multiplicity sample as essentially equivalent to the high multiplicity sample, but with unobserved intermediate planets, we find some evidence for an excess of planet pairs between the 2:1 and 3:1 Mean Motion Resonances in the low multiplicity sample. This possible excess may be the result of strong dynamical interactions near these or other resonances or it may be a byproduct of other evolutionary events or processes such as planetary collisions. Three planet systems show a significant excess of planets near the 2:1 Mean Motion Resonance that is not as prominent in either of the other samples. This observation may imply a correlation between strong dynamical interactions and observed planet number---perhaps a relationship between resonance pairs and the inclinations or orbital periods of additional planets. The period ratio distributions can also be used to identify targets to search for missing planets in the each of the samples, the presence or absence of which would have strong implications for planet formation and dynamical evolution models.