Webb maps uneven atmosphere of hot Jupiter WASP-17b

Astronomers have mapped an uneven atmosphere around WASP-17b using the James Webb Space Telescope, revealing how heat changes the outline of a distant giant planet. The University of Bristol announced the study on October 14. Led by Lili Alderson of Cornell University, the team applied a method called transmission strings to a hot Jupiter about 1,300 light-years from Earth.

The research, reported in Nature Astronomy, moves beyond treating the visible atmospheric edge as a uniform ring. Researchers track the planet as it passes in front of its star and analyse light filtered through different parts of its atmosphere. Developed by Bristol astrophysicists David Grant and Hannah Wakeford, the method reconstructs variations around that edge rather than averaging them together.

According to the paper, posted on arXiv on October 13, the observations span wavelengths from 0.6 to 12 micrometres and resolve differences both from east to west and from equator towards poles. The team estimates a roughly 650-kelvin temperature contrast between the morning and evening edges. These are inferred atmospheric conditions, rather than a direct photograph of the planet’s surface.

Bristol explains that winds carry heat from the permanently illuminated day side towards the dark night side, expanding the atmosphere near the evening equator. The morning edge is cooler after gas crosses the night side. The authors report that their findings agree with other measurements of the day and night sides, while water and carbon dioxide abundances are consistent with constant values around the atmospheric edge.

The results give researchers a way to test models of atmospheric circulation against spatially resolved observations, the authors say. Bristol describes the work as a successful demonstration that could support similar maps of other planets and eventually studies of weather-scale patterns. The measurements concern one hot Jupiter; extending the technique to additional worlds remains a next step, rather than a result already established.