A spatial map of the atmospheric limb of a hot Jupiter

Planets are inherently three-dimensional objects shaped by their thermal structure and dynamics. Observations of transiting exoplanets have begun to uncover this three-dimensional nature, with JWST measuring their dayside atmosphere structure with eclipse mapping and exploring spectroscopic asymmetries in the limbs of planets during transit. Here we apply the novel transmission strings mapping method to the hot Jupiter WASP-17 b. With this method, we are not only able to extract hemispheric limb asymmetries from east-to-west, but can also map equator-to-pole variations around the transmitting atmosphere as a function of angle, spanning 0.6–12 μm. We find a clear transition in the thermal scale height around the limb of the atmosphere, with an approximately 650 K temperature difference between the morning ( $$85{8}_{-233}^{+434}\,{\mathrm{K}}$$ 85 8 − 233 + 434 K ) and evening $$1{,}52{2}_{-114}^{+116}\,{\mathrm{K}}$$ 1 , 52 2 − 114 + 116 K ). These results are consistent with both nightside emission and dayside eclipse mapping measurements, and represent a fully comprehensive set of observations for a transiting exoplanet. We are also able to constrain the abundances of H ₂ O and CO ₂ to constant values around the limb, providing observational constraints for results from global circulation models. The transmission string technique, combined with the outstanding observability of WASP-17 b, pushes the study of exoplanet atmospheres further into a three-dimensional understanding of hot Jupiter dynamics and chemistry.