WASP-121b secondary eclipse in 2MASS K band

These are the first occultation observations of an extrasolar planet that were carried out with an instrument attached to a 1m class telescope (the SMARTS 1.3m). We find a highly significant eclipse depth of (0.228+/-0.023)%.

Together with other planet atmosphere measurements, including the Hubble Space Telescope near-infrared emission spectrum, current data support more involved atmosphere models with species producing emission and absorption features, rather than simple smooth blackbody emission. Analysis of the time difference between the primary and secondary eclipses and the durations of these events yields an eccentricity of e=0.0207+/-0.0153, which is consistent with the earlier estimates of low or zero eccentricity, but with a smaller error.