The case for a close-in perturber to GJ 436 b

TL;DR

This paper investigates the possibility of a close-in perturber planet affecting GJ 436 b's orbit, analyzing transit and radial velocity data to evaluate if such a planet could explain observed eccentricity and inclination changes.

Contribution

The study assesses the viability of a small, close-in perturber as an explanation for GJ 436 b's orbital characteristics using current observational data.

Findings

A close-in perturber remains a plausible explanation for GJ 436 b's eccentricity.

Radial velocity signals suggesting a perturber are likely spurious.

Transit timing variations support the possibility of an additional planet.

Abstract

The increasing number of transiting planets raises the possibility of finding changes in their transit time, duration and depth that could be indicative of further planets in the system. Experience from eclipsing binaries indeed shows that such changes may be expected. A first obvious candidate to look for a perturbing planet is GJ 436, which hosts a hot transiting Neptune-mass planet in an eccentric orbit. Ribas et al. (2008) suggested that such eccentricity and a possible change in the orbital inclination might be due to a perturbing small planet in a close-in orbit. A radial velocity signal of a 5 M_earth planet close to the 2:1 mean-motion resonance seemed to provide the perfect candidate. Recent new radial velocities have deemed such signal spurious. Here we put all the available information in context and we evaluate the possibility of a small perturber to GJ 436 b to explain its eccentricity and possible inclination change. In particular, we discuss the constraints provided by the transit time variation data. We conclude that, given the current data, the close-in perturber scenario still offers a plausible explanation to the observed orbital and physical properties of GJ 436 b.