Inflated planets and their low-mass companions

TL;DR

This paper demonstrates that very low-mass companion planets can maintain the eccentricity of inflated hot Jupiters like HD 209458b, explaining their inflated size without detectable stellar reflex velocities.

Contribution

It shows that sub-Earth mass companions can sustain eccentricity in hot Jupiters, supporting the idea that such companions are common and influence planetary inflation.

Findings

Low-mass companions can sustain non-zero eccentricity for billions of years.

Such companions produce reflex velocities below current detection limits.

Migration processes often produce low-mass companions to hot Jupiters.

Abstract

Various mechanisms have been proposed to explain the inflated size of HD 209458b after it became clear that it has no companions capable of producing a stellar reflex velocity greater than around 5 m/s. Had there been such a companion, the hypothesis that it forces the eccentricity of the inflated planet thereby tidally heating it may have been readily accepted. Here we summarize a paper by the author which shows that companion planets with masses as low as a fraction of an Earth mass are capable of sustaining a non-zero eccentricity in the observed planet for at least the age of the system. While such companions produce stellar reflex velocities which are fractions of a meter per second and hence are below the stellar jitter limit, they are consistent with recent theoretical work which suggests that the planet migration process often produces low-mass companions to short-period giants.