A Tendency Toward Alignment in Single-star Warm-Jupiter Systems
Malena Rice, Songhu Wang, Xian-Yu Wang, Guðmundur Stefánsson, Howard Isaacson, Andrew W. Howard, Sarah E. Logsdon, Heidi Schweiker, Fei Dai, Casey L. Brinkman, Steven Giacalone, Rae Holcomb
Abstract
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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>λ</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>6.2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>5.5</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>5.9</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>°</mml:mo> </mml:math> . 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.