Limits to the planet candidate GJ 436c

TL;DR

This study uses ground-based and archived observations to analyze the orbital inclination of GJ 436b and assess the existence of the proposed second planet GJ 436c, finding no strong evidence for its presence.

Contribution

The paper provides new constraints on the inclination change of GJ 436b and challenges the existence of the proposed GJ 436c planet candidate through combined observational analysis.

Findings

Measured orbital inclination change consistent with no significant variation.

Transit timing remains linear, indicating no additional planet influence.

Results strongly suggest GJ 436c is unlikely to exist.

Abstract

We report on H-band, ground-based observations of a transit of the hot Neptune GJ 436b. Once combined to achieve sampling equivalent to archived observations taken with Spitzer, our measurements reach comparable precision levels. We analyze both sets of observations in a consistent way, and measure the rate of orbital inclination change to be of 0.02+/-0.04 degrees in the time span between the two observations (253.8 d, corresponding to 0.03+/-0.05 degrees/yr if extrapolated). This rate allows us to put limits on the relative inclination between the two planets by performing simulations of planetary systems, including a second planet, GJ 436c, whose presence has been recently suggested (Ribas et al. 2008). The allowed inclinations for a 5 M_E super-Earth GJ 436c in a 5.2 d orbit are within ~7 degrees of the one of GJ 436b; for larger differences the observed inclination change can be reproduced only during short sections (<50%) of the orbital evolution of the system. The measured times of three transit centers of the system do not show any departure from linear ephemeris, a result that is only reproduced in <1% of the simulated orbits. Put together, these results argue against the proposed planet candidate GJ 436c.