A Tendency Toward Alignment in Single-Star Warm Jupiter Systems

TL;DR

This study shows that warm Jupiters around single stars tend to have aligned orbits, indicating quiescent formation, while lower-mass planets exhibit diverse orientations, implying dynamic post-formation interactions.

Contribution

First measurement of the spin-orbit angle for a warm Jupiter in a single-star system, revealing a tendency toward orbital alignment.

Findings

Warm Jupiters are more aligned than hot Jupiters in single-star systems.

Lower-mass Saturns show a wide range of spin-orbit angles.

Warm Jupiters likely form in aligned disks and experience less post-formation disturbance.

Abstract

The distribution of spin-orbit angles for systems with wide-separation, tidally detached exoplanets offers a unique constraint on the prevalence of dynamically violent planetary evolution histories. Tidally detached planets provide a relatively unbiased view of the primordial stellar obliquity distribution, since they cannot tidally realign within the system lifetime. We present the third result from our Stellar Obliquities in Long-period Exoplanet Systems (SOLES) survey: a measurement of the Rossiter-McLaughlin effect across two transits of the tidally detached warm Jupiter TOI-1478 b with the WIYN/NEID and Keck/HIRES spectrographs, revealing a sky-projected spin-orbit angle $\lambda=6.2^{+5.9}_{-5.5}$ degrees. Combining this new measurement with the full set of archival obliquity measurements, including two previous constraints from the SOLES survey, we demonstrate that, in single-star systems, tidally detached warm Jupiters are preferentially more aligned than closer-orbiting hot Jupiters. This finding has two key implications: (1) planets in single-star systems tend to form within aligned protoplanetary disks, and (2) warm Jupiters form more quiescently than hot Jupiters, which, in single-star systems, are likely perturbed into a misaligned state through planet-planet interactions in the post-disk-dispersal phase. We also find that lower-mass Saturns span a wide range of spin-orbit angles, suggesting a prevalence of planet-planet scattering and/or secular mechanisms in these systems.