James Webb Space Telescope observations reveal an uneven atmospheric edge around the giant planet WASP-17 b. An angle-dependent analysis found a hotter, more extended evening side and a cooler morning side. The peer-reviewed study reconstructs atmospheric properties from starlight during transit, bringing spatial detail to measurements previously averaged around the planet’s limb.
WASP-17 b, a giant gas planet orbiting close to its star, has a hotter and more extended evening atmospheric edge than its morning edge. A peer-reviewed analysis of James Webb Space Telescope observations mapped its uneven limb, the atmosphere seen around the planet’s outline as it crosses its star.[1], [2]
The analysis used observations collected in March 2023. Software fitted the changing starlight with a non-circular planetary outline and extracted spectra at different angles. Those spectra separate light by wavelength, revealing absorption by atmospheric molecules. The resulting map is an atmospheric reconstruction rather than a direct photograph.[1]
The hotter evening edge had a greater atmospheric scale height and stronger absorption features. Retrieved water and carbon-dioxide abundances were consistent around the limb. Methane and sulphur dioxide were less tightly constrained, and the analysis could not reliably establish variations in aerosols.[1]
The method’s smaller mapped regions required lower wavelength resolution and larger measurement uncertainties than limb-averaged methods. The model also assumed north–south symmetry. Within those conditions, the temperature contrast was consistent with circulation models predicting eastward atmospheric transport.[1]
