Recent observations from the James Webb Space Telescope (JWST) have unveiled intriguing atmospheric variations on the exoplanet WASP-121 b. By analyzing infrared starlight filtering through the planet's atmosphere during its transit in front of its host star, researchers identified a distinct pattern of light absorption that suggests significant differences between the planet's morning and evening sides.
According to the research team, the observed asymmetry in light absorption is attributed to varying temperatures and chemical compositions across the planet's atmosphere. "With its unprecedented observational quality, JWST offers the most detailed insights into distant worlds to date. By tracking how starlight absorption changes as WASP-121 b rotates, we can explore its atmosphere in remarkable detail," stated Cyril Gapp from the Max Planck Institute for Astronomy (MPIA).
The findings indicate that the evening terminator absorbs more starlight than the morning side, aligning with existing theories regarding powerful atmospheric winds that transport heat from the scorching day side to the cooler night side. These winds, which move eastward in sync with the planet's rotation, contribute to heightened temperatures in the evening region.
As temperatures increase, the atmosphere expands, creating a larger surface area for starlight absorption. Furthermore, data from JWST's Near-Infrared Spectrograph (NIRSpec) revealed a pronounced carbon monoxide (CO) signal towards the end of the transit, believed to be influenced by temperature variations rather than an increase in CO levels.
Interestingly, observations of water (H2O) presented a contrasting narrative. The data suggest a reduction in water molecules in the hotter regions of the atmosphere, likely due to high temperatures breaking down the molecules into hydrogen and oxygen. This supports the hypothesis that hot winds are responsible for warming the evening terminator.
A Planet of Extreme Conditions
WASP-121 b is an extreme example of a tidally locked gas giant, where one side perpetually faces its star while the other remains in darkness. The temperatures on the dayside can reach about 2770 Kelvin (nearly 2500 degrees Celsius), while the nightside cools to approximately 1000 Kelvin (around 725 degrees Celsius).
As the planet transits, it rotates slightly, allowing astronomers to observe various atmospheric sections. This rotation enables glimpses of the dawn and dusk regions, in addition to the predominantly visible night side.
Mapping Atmospheric Differences
To analyze the atmosphere, researchers studied how the planet's brightness fluctuated during the transit. They also examined light spectra, which reveal the presence of specific gases based on their absorption of distinct wavelengths. As WASP-121 b rotates, changes in the signal correspond to different longitudes, allowing for precise differentiation between the morning and evening terminators.
While previous models of gas giant atmospheres successfully replicated the general temperature asymmetry, the observed effects were more pronounced than predicted. This discrepancy hints at additional atmospheric processes, possibly including cooling effects or the presence of mineral-based clouds that could obscure infrared radiation.
Future Implications
As researchers refine their atmospheric models, they anticipate applying this innovative methodology to other ultra-hot gas giants. This could lead to a broader understanding of atmospheric conditions across diverse exoplanets, enriching our knowledge of their unique structures and behaviors.