Why are hot Jupiters around hotter stars often misaligned?
In plain words
Around cool stars, hot Jupiters usually orbit in the plane of the star's equator; around hotter stars their orbits are often tilted or even backward. Either tides straighten orbits only around cool stars, or the planets arrived differently.
Precise statement
Stellar obliquities measured by the Rossiter-McLaughlin effect are mostly small for host stars with $T_{\mathrm{eff}} < 6250\,\mathrm{K}$ and broadly distributed above. Determine whether this reflects tidal realignment acting through the convective envelope of cool stars or a primordial difference in formation, and determine the tidal dissipation rate needed for realignment without orbital decay.
What would settle it
Obliquity distributions versus stellar age, mass and planet mass for a large sample, compared with tidal models that predict realignment and decay together.
Related problems
- Special case of Which formation channel produces most hot Jupiters?