A Tendency Toward Alignment in Single-star Warm-Jupiter Systems

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, as 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 λ = 6.2 − 5.5 + 5.9 ° . 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.

Evidence for Hidden Nearby Companions to Hot Jupiters

“…Wider-orbiting warm Jupiters with periapses too large to undergo eccentric migration and tidal realignment have so far generally exhibited spin-orbit alignment (Rice et al 2022b), indicating a likely quiescent formation mechanism for these systems that is consistent with their high nearby companion rate. In our framework, these warm Jupiter planets did not experience planet-planet interactions that were strong enough to trigger eccentric migration, which would have otherwise caused the removal of their nearby companions and produced large misalignments.…”

The Spin–Orbit Misalignment of TOI-1842b: The First Measurement of the Rossiter–McLaughlin Effect for a Warm Sub-Saturn around a Massive Star

“…Previous obliquity measurements have focused on hot, massive planets around both hot and cool stars. Recent progress has been made for measuring obliquity for lower-mass planets and warm planets around cool stars (Schlaufman 2010;Sanchis-Ojeda et al 2013;Wang et al 2018Wang et al , 2022Anisman et al 2020;Dong et al 2022;Rice et al 2022b). Making R-M measurements for lower-mass planets-particularly those on wide orbits around hot, massive stars, in a poorly populated region of parameter space-is vital to test whether the M * /T eff versus obliquity relationship extends to populations other than e = 0 hot Jupiters.…”

Three Long-period Transiting Giant Planets from TESS*

“…A significant obliquity value for any of the three systems would further favor the high-eccentricity migration scenario triggered by secular gravitational interactions with outer companions as the cause of the close-in orbits (Petrovich & Tremaine 2016). Rice et al (2022b) found a tendency toward spin-orbit alignment of warm-Jupiter systems and suggest it as evidence of distinct migration mechanisms for the hot-and warm-Jupiter populations. The obliquity measurement of a bigger sample of warm Jupiters, particularly those that are eccentric like TOI 2338b and TOI 2589b, will help in confirming this claim.…”