JWST data and transmission strings reveal WASP-17b's uneven atmosphere
A Cornell-led team used JWST and a new transmission strings method to resolve the asymmetric limb of hot Jupiter WASP-17b, finding an inflated evening equator.
The story in focus
A Cornell-led team applied a new transmission strings mapping method to JWST observations of hot Jupiter WASP-17b, resolving its atmospheric limb from different angles. The planet appears slightly egg-shaped, with an inflated evening equator consistent with heat transport by winds; findings were published in Nature Astronomy.
- Transmission strings tracks the planet during transit to measure composition around the atmospheric limb from multiple angles.
- WASP-17b's limb is slightly egg-shaped, with one more extended side.
- An inflated evening equatorial region matches predictions of winds carrying heat from the day side toward the night side.
What the method resolves
The transmission strings approach, also called transit mapping, observes an exoplanet as it crosses in front of its star. It records the composition of light around the planet's atmospheric edge, or limb, from different angles. Earlier modeling extracted a spectrum averaged across the entire limb.
Applied to NASA's James Webb Space Telescope observations of WASP-17b, the method yielded a spatial map of the atmosphere instead of a single averaged radius. The Cornell-led team describes the planet's contours as circle-like but slightly egg-shaped.
Winds and chemistry on a hot Jupiter
WASP-17b orbits a star more than 1,000 light years from Earth. Its atmosphere features permanent day and night sides. The mapping found an inflated region on the evening side of the equator, where winds are interpreted as carrying heat from the illuminated side toward the shadowed side.
Team members said the temperature contrast between morning and evening sides and the presence of water and carbon dioxide around the limb agree with theoretical predictions and other modeling techniques. The findings were published Oct. 14 in Nature Astronomy.
What comes next
The team presents the result as proof of concept that exoplanets are three-dimensional objects and that transmission strings can be applied to other candidates. The researchers say the work begins to distinguish conditions across latitudes, not only between day and night sides.
Does the new mapping support existing models of WASP-17b's atmosphere?
Yes. The team reports that the planet's chemical composition and temperature shifts agree with theoretical predictions and other modeling techniques, including the expected morning-to-evening temperature difference and consistent water and carbon dioxide around the limb.
Sources & further reading
- Pulling strings: New method maps exoplanet’s true shape | Cornell Chronicle - Pulling strings: New method maps exoplanet’s true shape ↗news.cornell.edu
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