Quantifying the Similarity of Planetary System Architectures

TL;DR

This paper introduces a novel Weighted Energy Distance metric to quantify and compare the architectures of planetary systems, revealing an order from compact systems to those with distant giants, and providing tools for catalog comparison.

Contribution

The paper presents a new WED metric for planetary system comparison and extends it to ICED for set comparisons, with an automatic Sequencer tool to identify system progressions.

Findings

WED effectively characterizes planetary system arrangements.

The Sequencer identifies a progression from small to giant planet systems.

The ICED metric enables comparison between different planetary system catalogs.

Abstract

The planetary systems detected so far already exhibit a wide diversity of architectures, and various methods are proposed to study quantitatively this diversity. Straightforward ways to quantify the difference between two systems and more generally, two sets of multiplanetary systems, are useful tools in the study of this diversity. In this work we present a novel approach, using a Weighted extension of the Energy Distance (WED) metric, to quantify the difference between planetary systems on the logarithmic period-radius plane. We demonstrate the use of this metric and its relation to previously introduced descriptive measures to characterise the arrangements of Kepler planetary systems. By applying exploratory machine learning tools, we attempt to find whether there is some order that can be ascribed to the set of Kepler multiplanet system architectures. Based on WED, the 'Sequencer', which is such an automatic tool, identifies a progression from small and compact planetary systems to systems with distant giant planets. It is reassuring to see that a WED-based tool indeed identifies this progression. Next, we extend WED to define the Inter-Catalogue Energy Distance (ICED) - a distance metric between sets of multiplanetary systems. We have made the specific implementation presented in the paper available to the community through a public repository. We suggest to use these metrics as complementary tools in attempting to compare between architectures of planetary system, and in general, catalogues of planetary systems.