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

Abstract

The mechanisms responsible for generating spin-orbit misalignments in exoplanetary systems are still not fully understood. It is unclear whether these misalignments are related to the migration of hot Jupiters or are a consequence of general star and planet formation processes. One promising method to address this question is to constrain the distribution of spin-orbit angle measurements for a broader range of planets beyond hot Jupiters. In this work, we present the sky-projected obliquity ( $\lambda =-68\buildrel{\circ}\over{.} {1}_{-14.7}^{+21.2}$ ) for the warm sub-Saturn TOI-1842b, obtained through a measurement of the Rossiter-McLaughlin effect using WIYN/NEID. From this, we determine the resulting 3D obliquity (ψ) to be $\psi =73\buildrel{\circ}\over{.} {3}_{-12.9}^{+16.3}$ . As the first spin-orbit angle determination made for a sub-Saturn-mass planet around a massive ( M _* = 1.45 M _☉) star, our result presents an opportunity to examine the orbital geometries for new regimes of planetary systems. When combined with archival measurements, our observations of TOI-1842b support the hypothesis that the previously established prevalence of misaligned systems around hot, massive stars may be driven by planet-planet dynamical interactions. In massive stellar systems, multiple gas giants are more likely to form and can then dynamically interact with each other to excite spin-orbit misalignments.