Atmospheric Waves Driving Variability and Cloud Modulation on a Planetary-Mass Object

Planetary-mass objects and brown dwarfs at the transition from relatively red L dwarfs to bluer mid-T dwarfs (T_eff∼1300 K) show enhanced spectrophotometric variability. An open question is whether this variability is caused by atmospheric planetary-scale (Kelvin or Rossby) waves or by large spots associated with the precipitation of silicate and metal clouds. We applied both waves and spotted models to fit near-infrared (NIR), multi-band (Y/J/H/K) photometry of SIMP J013656.5+093347 (hereafter SIMP0136), collected at the Canada-France-Hawaii Telescope using the Wide-field InfraRed Camera. SIMP0136 is a planetary-mass object (12.7±1.0 M_J) at the L/T transition (T2±0.5) known to exhibit light curve evolution over multiple rotational periods. We measure the maximum peak-to-peak variability of 6.17±0.46%, 6.45±0.33%, 6.51±0.42%, and 4.33±0.38% in the Y, J, H, and K bands respectively, and find evidence that wave models are preferred for all four NIR bands. Furthermore, we determine the spot size necessary to reproduce the observed variations is larger than the Rossby deformation radius and Rhines scale, which is unphysical. Through the correlation between light curves produced by the waves and associated color variability, we find evidence of planetary-scale, wave-induced cloud modulation and breakup, similar to Jupiter's atmosphere and supported by general circulation models. We also detect a 93.8^∘±7.4^∘ (12.7σ) phase shift between the H-K and J-H color time series, providing evidence for complex vertical cloud structure in SIMP0136's atmosphere.