In a groundbreaking achievement, astronomers have successfully mapped the three-dimensional atmosphere of an exoplanet orbiting a distant star for the first time. This unprecedented study of the gas giant WASP-18b, located 400 light years from Earth, has unveiled significant temperature variations and distinct atmospheric regions on this alien world.
Utilizing the James Webb Space Telescope, researchers tracked subtle changes in brightness as WASP-18b passed behind its host star. This technique allowed scientists to create a detailed weather map of the exoplanet, moving beyond the traditional view of these distant worlds as mere points of light in the sky. The mapping process transforms our understanding of exoplanets into tangible environments that can be examined layer by layer.
WASP-18b is classified as an “ultra-hot Jupiter,” with a mass roughly ten times that of our own Jupiter, orbiting its star in just 23 hours. Its extreme temperatures, which can reach nearly 5,000 degrees, are sufficient to break apart water vapor molecules within its atmosphere. The new mapping technique has pinpointed where these harsh conditions manifest across the planet.
The innovation behind this achievement lies in a method known as spectroscopic eclipse mapping, which was applied here for the first time using data from the James Webb Space Telescope. This complex technique involves measuring the faint light emitted by WASP-18b as it passes behind its star. By observing the changes in brightness, astronomers can correlate specific regions of the planet with variations in light intensity.
A key aspect of this mapping technique is the ability to observe eclipses across multiple wavelengths simultaneously. Different wavelengths penetrate various layers of the atmosphere because molecules absorb light differently at distinct wavelengths. For example, water vapor absorbs certain infrared wavelengths while allowing others to pass through. This allows researchers to construct brightness maps that can be translated into temperature profiles, ultimately creating a three-dimensional representation that includes latitude, longitude, and altitude.
The resultant map has identified spectroscopically unique regions across the dayside of WASP-18b, the hemisphere consistently facing its star due to tidal locking. These regions exhibit substantial differences in temperature and may also vary in chemical composition, underscoring the complexity and diversity of atmospheres even in distant planets that cannot be directly imaged.
This pioneering technique opens the door to a new era in exoplanet research. With hundreds of hot Jupiters like WASP-18b among the more than 6,000 confirmed exoplanets, many of which are observable by the James Webb Space Telescope, astronomers can begin to view these distant worlds not as simplistic dots but as dynamic, three-dimensional environments. Future observations could enhance the spatial resolution of these atmospheric maps, and applying this method to other hot Jupiters will reveal the atmospheric variety within this category of planets.
What began as a proof of concept for mapping an extreme exoplanet may soon evolve into a comprehensive survey, enabling scientists to understand exoplanets as real places with geography, weather patterns, and atmospheric structures that can be thoroughly investigated.
