Universe Today | 2023 Apr 30
In our solar system, the planetary orbits all have a similar orientation. Their orbital planes vary by a few degrees, but roughly the planets all orbit in the same direction. This invariable plane as it’s known also has an orientation within a few degrees of the Sun’s rotational plane. Most planetary systems have a similar arrangement, where planetary orbits and stellar rotation are roughly aligned, but a few exoplanets defy this trend, and we aren’t entirely sure why.
Common orientation within a planetary system makes sense given how planetary systems form. The protostellar cloud out of which a star and its planets form usually has some inherent rotational momentum. As a star begins to coalesce, a protoplanetary disk forms around the star. Since the planets form within this disk, they all end up with similar orbits. Things can be more complicated with binary or multiple-star systems, but you’d expect single-star planetary systems to have an invariable plane similar to ours. However, this isn’t true for a planetary system known as WASP-131, as a recent study shows. ...
When the team analyzed the rotation of WASP-131, they found it wasn’t similar to that of its planet. The orbit of 131b is tilted about 160 degrees from the rotational plane of the star, meaning that it is in a high, almost polar retrograde orbit. Of course, this raises the question of just how the planet could have gotten such an odd orbit. ...
WASP-131 b with ESPRESSO I: A Bloated Sub-Saturn on a Polar
Orbit around a Differentially Rotating Solar-type Star ~ L. Doyle et al
- Monthly Notices of the RAS (online 29 April 2023) DOI: 10.1093/mnras/stad1240
- arXiv > astro-ph > arXiv:2304.12163 > 24 Apr 2023