Astronomers have successfully produced the first three-dimensional map of an exoplanet”s atmosphere, highlighting distinct temperature zones. This innovative research, co-led by a Cornell University expert, focuses on the gas giant known as WASP-18b, categorized as an “ultra-hot Jupiter,” located approximately 400 light years from Earth.
The temperature map of WASP-18b utilizes a method called 3D eclipse mapping, a technique that enhances observations made by NASA”s James Webb Space Telescope (JWST). This effort builds upon a two-dimensional model released by the same research team earlier in 2023, which showcased the potential of eclipse mapping.
“Eclipse mapping allows us to image exoplanets that we can”t see directly, because their host stars are too bright,” stated Ryan Challener, a postdoctoral associate in the Department of Astronomy. “With this telescope and this new technique, we can start to understand exoplanets similarly to how Earth-based telescopes have long observed Jupiter”s features.”
Challener is the lead author of the upcoming study titled “Horizontal and Vertical Exoplanet Thermal Structure from a JWST Spectroscopic Eclipse Map,” set to be published on October 28 in Nature Astronomy. The research team includes over 30 co-authors, among them Megan Wiener Mansfield, an assistant professor of astronomy at the University of Maryland, who played a significant role in co-leading the project.
Detecting exoplanets poses significant challenges due to their dim brightness, which is often less than 1% of the light emitted by their host stars. The eclipse mapping technique involves measuring minute changes in brightness as the planet passes behind its star, thus revealing various parts of the planet”s surface.
By linking these subtle variations in light to specific regions, scientists can generate a brightness map that, when analyzed across multiple wavelengths, can be converted into a three-dimensional temperature profile representing latitude, longitude, and altitude.
“You”re observing changes in tiny portions of the planet as they disappear and reappear into view,” Challener explained. “This process is extraordinarily challenging.”
With a mass equivalent to approximately ten times that of Jupiter, WASP-18b completes an orbit in just 23 hours, exposing it to intense temperatures nearing 5,000 degrees Fahrenheit. This extreme environment provided a strong signal, making it an ideal candidate for testing the new mapping technique.
While the previous two-dimensional map utilized a single wavelength of light, the new three-dimensional map re-evaluated data from JWST”s Near-Infrared Imager and Slitless Spectrograph (NIRISS) across a range of wavelengths. Each wavelength corresponds to different temperatures and altitudes within WASP-18b”s atmosphere, enabling the construction of a comprehensive 3D map.
Challener noted that if a map is created at a wavelength that water vapor absorbs, it reveals the water layer in the atmosphere, whereas wavelengths that do not absorb will penetrate deeper, allowing for a more complete picture of the atmospheric temperatures.
The findings confirmed the presence of spectroscopically distinct regions on WASP-18b”s visible “dayside,” which is perpetually facing its star due to its tidally locked orbit. A pronounced “hotspot” emerges where the most intense starlight strikes, while cooler regions form a ring around the planet”s outer edges.
Interestingly, measurements indicated lower water vapor levels in the hotspot compared to the planet”s overall average. “We believe this suggests that the planet”s extreme heat is beginning to break down the water,” Challener observed. “While this had been theorized, it”s thrilling to witness it through actual observations.”
Further observations using JWST could enhance the spatial resolution of this initial 3D eclipse map. The technique is anticipated to shed light on the temperature structures of numerous other hot Jupiters, contributing to the understanding of more than 6,000 confirmed exoplanets to date.
“This new technique will be applicable to many exoplanets that we can observe with the James Webb Space Telescope,” Challener concluded. “We can start to analyze exoplanets in three dimensions as a collective group, which is extremely exciting.”
The research received support from JWST”s Transiting Exoplanet Community Early Release Science Program.
