Swift alignment of young eccentric orbits: leveraging warm Jupiter dynamics to probe tidal dissipation in stars

A very recent series of discoveries have revealed a surprising trend: warm Jupiters (WJs) exhibit a astonishing level of spin-orbit alignment with their host stars, a sharp departure from the widely distributed stellar obliquities observed in the hot Jupiter population. Additionally, this alignment appears to be independent of orbital eccentricity, even at values as high as e~0.8. This last finding challenges planet formation and migration models, which typically predict the existence of extreme eccentricities alongside large inclinations. Could such orbital architectures be primordial? If not primordial, is it conceivable for the alignment of stellar spin and orbit to take place before an orbit becomes circular? This study delves into the latter possibility, deviating from the conventional belief that stellar realignment is markedly less effective than orbital circularization according to established tidal theories. This is indeed the case when inclination damping, orbital circularization and orbital decay all respond to a single mechanism of tidal dissipation (enclosed in a single value of the tidal quality factor Q). But this is no longer true if different components of the tidal potential excite different types of waves throughout the stellar interior. One example is the excitation of inertial waves in the convective regions of a rapidly spinning star, which can be triggered by a specific component of the tidal potentials when misalignment is significant. When these waves damp, the energy losses can be equivalent to extremely low values of Q (10²-10³). For WJs, these Q values translate into significant energy changes in only a few hundred years. Most crucially, the energy loss acts at the expense of the specific tidal potential responsible for the excitation. Thus, these waves can damp relative inclinations without leading orbital decay nor circularization. This effect can be even more dramatic in the short-lived pre-main sequence phase, when the star is of larger extent, rapidly spinning and fully convective. This work presents a detailed dynamical exploration of the effect of inertial waves in the swift spin-orbit realignment of young, eccentric orbits, offering an entirely novel explanation for the mysterious architectures of WJ systems, while exploiting a physically justified mechanism to enhance the tidal dissipation properties of host stars.