Scientists have created for the first time a three-dimensional map of the atmosphere of a distant planet.
Using data from James Webb Space Telescope (JWST) and a technique known as eclipse mapping, researchers discovered different temperature zones in the atmosphere of the exoplanet WASP-18b, a gas giant located about 400 light-years from Earth. The same process could soon help scientists map changes in temperature and cloud structure on other distant planets, according to a study published Oct. 28 in the journal. Nature Astronomy.
WASP-18b's mass is about 10 times that of Jupiter, and its year is only 23 hours long. It is tidally locked to its star, meaning that one side of the planet is always facing the star, while the other side is always dark.
As a planet begins to pass behind its star, the star blocks more and more of the light reflected by the planet until the planet is completely eclipsed as seen from our solar system. Eclipse mapping takes advantage of this progressive change. By measuring how the planet's light changes as it is hidden and revealed, scientists can determine the temperature in different regions and at different altitudes in the planet's atmosphere.
“You're looking for changes in tiny parts of the planet as they disappear and come back into view, so it's extremely difficult,” Challener said.
In the new study, scientists relied on previous 2D temperature map WASP-18b, using different wavelengths of light to create a more detailed 3D map of the atmosphere. For example, they used data on the wavelengths absorbed by water to map the exoplanet's wet upper atmosphere. The wavelengths that the water did not absorb traveled to lower altitudes, allowing JWST to preferentially look at different levels of the planet's atmosphere depending on the wavelengths being studied.
The team found that WASP-18b has two distinct temperature regions on its dayside. It has a circular “hot spot” in the area facing directly toward the star and receiving the most sunlight. Behind it is a cooler ring that extends to the visible edge of the planet. This suggests that atmospheric winds cannot completely redistribute heat from the star throughout the planet.
Scientists also noticed less water in the hot spot than the planetary average. This could mean that the temperature at the hot spot is high enough to break apart water molecules in the atmosphere, the researchers suggested.
“We think this is evidence that the planet is so hot in this region that water is starting to break down,” Challener said. “This was predicted by theory, but it's really interesting to see it in real-life observations.”
Additional measurements from JWST could improve the resolution of WASP-18b's atmospheric map and allow scientists to study the atmospheres of other similar gas giants.
“This new technique will be applicable to many, many other planets we can see with the James Webb Space Telescope“We can start to understand exoplanets in 3D as a population, and that's very exciting,” Challener said.
