TOI-1685b transit spectra from JWST

We obtain transmission and emission spectra of the planet and characterize the properties of the phase curve, including its amplitude and offset. The transmission spectrum rules out clear H2-dominated atmospheres, while secondary atmospheres (made of water, methane, sulfur dioxide, or carbon dioxide) cannot be statistically distinguished from a flat line.

The emission spectrum is featureless and consistent with a dark surface, ruling out carbon dioxide-, sulfur dioxide-, or methane-dominated atmospheres thicker than 100 mbar. Collecting all evidence, the properties of TOI-1685 b are consistent with a blackbody with no heat redistribution and a low albedo, with a dayside brightness temperature 0.99+/-0.07 times that of a perfect blackbody in the NIRSpec NRS2 wavelength range (3.823-5.172um).