Atmospheric differences between morning and evening sides of planet WASP-39 b revealed

Recent observations of the hot Jupiter WASP-39 b show distinct differences between its morning and evening atmospheric limbs. By comparing five different climate models with data from the JWST telescope, researchers analyzed how clouds, chemical processes, and temperature variations contribute to these observed asymmetries, though current models still struggle to fully replicate the measured carbon dioxide signal.

Star system: WASP-39 | Distance from the Sun: 702 light years

The hot Jupiter exoplanet WASP-39 b exhibits significant differences between the two sides of its atmosphere that transition from day to night. Observations show that the evening side has a larger transit radius and a stronger signature of carbon dioxide compared to the morning side. This phenomenon highlights how the atmosphere of a gas giant planet is not uniform, as shifting winds and chemical changes create unique conditions at the boundaries between day and night.

To understand these findings, researchers compared simulations from five different general circulation models. These computer programs simulate the global weather and climate patterns on the planet. They factored in complex processes like the movement of heat around the globe, chemical reactions occurring away from their natural equilibrium, and the presence of clouds or hazes. By applying these models to the planet, they tested if current theoretical understanding matches the clear, measurable data provided by the James Webb Space Telescope.

While the models consistently predicted similar temperature differences between the morning and evening, they faced challenges in matching the strength of the observed carbon dioxide feature. Some early models incorrectly predicted strong methane signatures in the morning, which were not actually seen in the data. Including chemical processes that move air across the planet helped explain the missing methane. However, reproducing the full scale of the carbon dioxide asymmetry remains a challenge, suggesting that future models must incorporate more detailed information about cloud formation and atmospheric composition.

Key findings
The evening side of WASP-39 b has a larger transit radius by approximately 400 parts per million.
The evening side shows a stronger 4.3 micrometer carbon dioxide signal than the morning side.
Disequilibrium chemistry helps explain the absence of methane features in the observed spectrum.
Current computer models cannot fully replicate the observed 2000 parts per million asymmetry in the carbon dioxide feature.
Discrepancies suggest a need for improved models integrating cloud microphysics and feedback across various conditions.

Scientific study

Limb Asymmetries on WASP-39b: A Multi-GCM Comparison of Chemistry, Clouds, and Hazes (external link)