# The multiplicity distribution of Kepler's exoplanets

## TL;DR

This study infers the true multiplicity distribution of Kepler's exoplanet systems using Bayesian methods, revealing many hidden planets and challenging the need for multiple population models.

## Contribution

It demonstrates that a single Zipfian distribution can explain Kepler's observed multiplicities, providing an alternative to dichotomous population models.

## Key findings

- A single Zipfian model fits Kepler data well.
- Approximately 2,393 hidden planets are inferred in the studied systems.
- About half of single-transiting systems likely host additional planets.

## Abstract

The true multiplicity distribution of transiting planet systems is obscured by strong observational biases, leading low-multiplicity systems to be overrepresented in the observed sample. Using the Kepler FGK planet hosts, we employ approximate Bayesian computation to infer the multiplicity distribution by comparing simulated catalogs to the observed one. After comparing a total of ten different multiplicity distributions, half of which were two-population models, to the observed data, we find that a single-population model following a Zipfian distribution is able to explain the Kepler data as well as any of the dichotomous models we test. Our work provides another example of a way to explain the observed Kepler multiplicities without invoking a dichotomous planet population. Using our preferred Zipfian model, we estimate that an additional $2393_{-717}^{+904}$ planets likely reside in the 1537 FGK Kepler systems studied in this work, which would increase the planet count by a factor of $2.22_{-0.36}^{+0.46}$. Of these hidden worlds, $663_{-151}^{+158}$ are expected to reside in ostensibly single-transiting-planet systems, meaning that an additional planet(s) is expected for approximately 1-in-2 such Kepler systems.