A Planet Candidate Orbiting near the Hot Jupiter TOI-2818 b Inferred through Transit Timing

TL;DR

This paper reports the detection of transit timing variations in the hot Jupiter TOI-2818 b, suggesting the presence of an unseen planetary companion near a mean-motion resonance, with implications for planetary system dynamics.

Contribution

It introduces evidence for a potential additional planet near resonance inferred from TTVs, challenging previous explanations like orbital decay or stellar acceleration.

Findings

Transit timing variations suggest a possible unseen planet.

Orbital decay rate is too high to be explained by tidal dissipation.

Radial velocity data rules out a long-period stellar companion.

Abstract

TOI-2818 b is a hot Jupiter orbiting a slightly evolved G-type star on a 4.04-day orbit that shows transit timing variations (TTVs) suggestive of a decreasing orbital period. In the most recent year of TESS observations, transits were observed $\sim$8 minutes earlier than expected for a constant period. The implied orbital decay rate is $1.35 \pm 0.25$ s yr$^{-1}$, too fast to be explained by tidal dissipation even considering the evolved nature of the host star. Radial velocity monitoring rules out the possibility that the apparent change in period is due to a steady acceleration of the star by a long-period companion. Apsidal precession due to the tidal distortion of the planet is also physically implausible. The most plausible explanation for the TTVs appears to be gravitational perturbations from a hitherto undetected planet with mass $\lesssim$$10\,M_\oplus$ that is in (or near) a mean-motion resonance with the hot Jupiter. Such a planet could be responsible for the observed TTVs while avoiding detection with the available radial velocity and transit data.