On The Relative Sizes of Planets Within Kepler Multiple Candidate Systems

TL;DR

This study analyzes the relative sizes of planets in Kepler multi-planet systems, revealing that larger planets tend to be farther from the star when at least one is Neptune-sized or larger, but no such pattern exists for smaller planets.

Contribution

It provides the first statistical analysis of size and orbital ordering correlations among planets in Kepler multi-planet systems, correcting for detection biases.

Findings

Larger planets (≥ Neptune-sized) are often farther from the star.

No size-location correlation for smaller planets (< Neptune-sized).

68% of pairs with at least one large planet have the larger planet farther out.

Abstract

We present a study of the relative sizes of planets within the multiple candidate systems discovered with the $Kepler$ mission. We have compared the size of each planet to the size of every other planet within a given planetary system after correcting the sample for detection and geometric biases. We find that for planet-pairs for which one or both objects is approximately Neptune-sized or larger, the larger planet is most often the planet with the longer period. No such size--location correlation is seen for pairs of planets when both planets are smaller than Neptune. Specifically, if at least one planet in a planet-pair has a radius of $\gtrsim 3R_\oplus$, $68\pm 6%$ of the planet pairs have the inner planet smaller than the outer planet, while no preferred sequential ordering of the planets is observed if both planets in a pair are smaller than $\lesssim3 R_\oplus$.