2024/09/10 by Caleb Lammers, Joshua N. Winn, Lammers, Caleb +1 · 3 citations
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Earth and Planetary Astrophysics (astro-ph.EP) #FOS: Physical sciences #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2409.06697
openalex publication_date 2024/09/10 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Super-puffs are low-density planets of unknown origin and composition. If they form by accreting nebular gas through a circumplanetary disk, one might expect super-puffs to be spinning quickly. Here, we derive upper limits on the rotational oblateness of the super-puff Kepler-51d, based on precise transit observations with the NIRSpec instrument aboard the James Webb Space Telescope. The absence of detectable oblateness-related anomalies in the light curve leads to an upper limit of about 0.15 on the planet's sky-projected oblateness. Assuming the sky-projected oblateness to be representative of the true oblateness, the rotation period of Kepler-51d is \gtrsim 40 hours, or equivalently, its rotation speed is \lesssim 42% of the breakup speed. Alternatively, if the apparently low density of Kepler-51d is due to an opaque planetary ring, the ring must be oriented within 30° of face-on and have an inner radius smaller than 1.2 times the planet's radius. Separately, the lack of anomalies exceeding 0.01% in the ingress and egress portions of the light curve places a constraint on the model of Wang & Dai, in which the planet's apparently low density is due to a dusty outflowing atmosphere.