Hot Jupiters

The eccentricity cascade

The retrograde orbit of the hot Jupiter HAT-P-7b has long posed a dynamical puzzle, as its known stellar companion is too distant to drive migration through conventional mechanisms. In this project, we show that the system is not as simple as it once appeared. By combining radial velocity data with transit timing variations, we uncover evidence for a previously hidden third star: a nearby, eccentric M-dwarf.

This additional companion opens the door to a new migration pathway we call the eccentricity cascade. In this picture, a distant star first excites the eccentricity of the intermediate companion, which then passes that dynamical disturbance inward, eventually “kicking” the planet onto a highly eccentric and misaligned orbit. We develop an analytic model to describe this process and show that intermediate companions can act as effective bridges, allowing even very distant perturbers to drive hot-Jupiter formation. The eccentricity cascade dramatically broadens the kinds of stellar systems that can produce hot Jupiters, making their origins far less restrictive than previously thought.

Paper link: companion characterization in HAT-P-7, analytical model for the eccentricity cascade