A Systematic Search for Trojan Planets in the Kepler data

TL;DR

This study systematically searched for Trojan planets in Kepler data, finding no candidates but highlighting the potential for undetected Trojans outside the transit plane and emphasizing the need for extensive computational analysis.

Contribution

It presents the first large-scale systematic search for extrasolar Trojans in Kepler data, considering non-transiting configurations and discussing detection challenges.

Findings

No convincing Trojan candidates found in the data.

Earth-sized Trojans could exist but remain undetectable with current transit methods.

Some KOIs might be Trojans orbiting outside the transiting plane.

Abstract

Trojans are circumstellar bodies that reside in characteristic 1:1 orbital resonances with planets. While all the trojans in our Solar System are small (< ~100 km), stable planet-size trojans may exist in extrasolar planetary systems, and the Kepler telescope constitutes a formidable tool to search for them. Here we report on a systematic search for extrasolar trojan companions to 2244 known Kepler Objects of Interest (KOIs), with epicyclic orbital characteristics similar to those of the Jovian trojan families. No convincing trojan candidates are found, despite a typical sensitivity down to Earth-size objects. This fact can however not be used to stringently exclude the existence of trojans in this size range, since stable trojans need not necessarily share the same orbital plane as the planet, and thus may not transit. Following this reasoning, we note that if Earth-sized trojans exist at all, they are almost certainly both present and in principle detectable in the full set of Kepler data, although a very substantial computational effort would be required to detect them. On the same token, we also note that some of the existing KOIs could in principle be trojans themselves, with a primary planet orbiting outside of the transiting plane. A few examples are given for which this is a readily testable scenario.