Are Tidal Effects Responsible for Exoplanetary Spin-Orbit Alignment?

Understand

The obliquities of planet-hosting stars are clues about the formation of planetary systems.

• Previous observations led to the hypothesis that for close-in giant planets, spin-orbit alignment is enforced by tidal interactions.
• Here, we examine two problems with this hypothesis.
• First, Mazeh and coworkers recently used a new technique -- based on the amplitude of starspot-induced photometric variability -- to conclude that spin-orbit alignment is common even for relatively long-period planets, which would not be expected if tides were responsible.