- Rubenzahl, Ryan A;
- Dai, Fei;
- Howard, Andrew W;
- Chontos, Ashley;
- Giacalone, Steven;
- Lubin, Jack;
- Rosenthal, Lee J;
- Isaacson, Howard;
- Batalha, Natalie M;
- Crossfield, Ian JM;
- Dressing, Courtney;
- Fulton, Benjamin;
- Huber, Daniel;
- Kane, Stephen R;
- Petigura, Erik A;
- Robertson, Paul;
- Roy, Arpita;
- Weiss, Lauren M;
- Beard, Corey;
- Hill, Michelle L;
- Mayo, Andrew;
- Mocnik, Teo;
- Murphy, Joseph M Akana;
- Scarsdale, Nicholas
We measured the Rossiter-McLaughlin effect of WASP-107b during a single transit with Keck/HIRES. We found the sky-projected inclination of WASP-107b's orbit, relative to its host star's rotation axis, to be |λ| = 118+19-38degrees. This confirms the misaligned/polar orbit that was previously suggested from spot-crossing events and adds WASP-107b to the growing population of hot Neptunes in polar orbits around cool stars. WASP-107b is also the fourth such planet to have a known distant planetary companion. We examined several dynamical pathways by which this companion could have induced such an obliquity in WASP-107b. We find that nodal precession and disk dispersal-driven tilting can both explain the current orbital geometry while Kozai-Lidov cycles are suppressed by general relativity. While each hypothesis requires a mutual inclination between the two planets, nodal precession requires a much larger angle, which for WASP-107 is on the threshold of detectability with future Gaia astrometric data. As nodal precession has no stellar type dependence, but disk dispersal-driven tilting does, distinguishing between these two models is best done on the population level. Finding and characterizing more extrasolar systems like WASP-107 will additionally help distinguish whether the distribution of hot-Neptune obliquities is a dichotomy of aligned and polar orbits or if we are uniformly sampling obliquities during nodal precession cycles.