Astrophysics (index)

Retrograde Hot Jupiter

(large hot planet orbiting opposite the expected direction)

A Retrograde Hot Jupiter is a Hot Jupiter with a retrograde orbit, i.e., opposite the direction of the star's rotation. Since systems are assumed to form from rotating clouds, forming both the star's rotation and the planets' orbits from the initial cloud rotation, this is a mystery. Many Hot Jupiters also have other highly unusual orbits, e.g., polar.

It is assumed that either the Hot Jupiter's orbit was disturbed or the star flipped its spin.