Transit timing variations for planets coorbiting in the horseshoe regime

TL;DR

This paper investigates transit timing variations caused by coorbiting planets in horseshoe orbits, proposing methods to identify such configurations and estimate planetary masses from observational data.

Contribution

It introduces a semi-analytic model to analyze transit timing variations for horseshoe orbit planets, enabling mass ratio and total mass estimation from transit data.

Findings

Transit timing variations can constrain planetary mass ratios.

Total planetary mass relative to the star can be inferred from timing data.

Characteristic TTV traits help identify horseshoe coorbiting planets.

Abstract

While not detected yet, pairs of exoplanets in the 1:1 mean motion resonance probably exist. Low eccentricity, near-planar orbits, which in the comoving frame follow the horseshoe trajectories, are one of the possible stable configurations. Here we study transit timing variations produced by mutual gravitational interaction of planets in this orbital architecture, with the goal to develop methods that can be used to recognize this case in observational data. In particular, we use a semi-analytic model to derive parametric constraints that should facilitate data analysis. We show that characteristic traits of the transit timing variations can directly constrain the (i) ratio of planetary masses, and (ii) their total mass (divided by that of the central star) as a function of the minimum angular separation as seen from the star. In an ideal case, when transits of both planets are observed and well characterized, the minimum angular separation can also be inferred from the data. As a result, parameters derived from the observed transit timing series alone can directly provide both planetary masses scaled to the central star mass.