The James Webb Space Telescope conducted a detailed analysis of WASP-39b, revealing the different atmospheric conditions on the "morning" and "evening" sides of a distant planet. This is a tidally locked exoplanet with different atmospheric conditions in the morning and evening. It is cooler in the morning and hotter in the evening.
Measuring the atmospheres of exoplanets (planets outside our solar system) using powerful telescopes has been available for some time. However, the atmosphere has long been thought to be the same across the entire planet.
The new analysis, published July 15 in the journal Nature, focuses on a planet with an extraordinary atmosphere, revealing its unique "morning" and "evening" sides. The study was led by the Space Telescope Science Institute, with part of the analysis conducted by a researcher at Imperial College London.
The giant planet, named WASP-39b, has a larger radius than Jupiter but a similar mass to Saturn and orbits a star about 700 light-years away from Earth. It is also very close to its star, which causes its daily maximum surface temperature to exceed 1000°C (1800°F), meaning that it takes the same amount of time to complete one "daily" rotation as it does to complete one orbital rotation.
This also means that it is "tidally locked": the same side of the planet always faces the star, just like the same side of the moon always faces the Earth. This creates a constant "day" and a constant "night" side of the planet, but crucially, there are also "morning" and "evening" sides in between.
Dr James Kirk from the Department of Physics at Imperial College London said: "There are no such planets in the solar system, but most of the planets we have observed orbiting distant stars are relatively close and have short orbits, such as WASP-39b. Now, we have been able to test our theories about these planets and directly measure the twilight and twilight aspects of exoplanets over a wide range of wavelengths for the first time."
Néstor Espinoza, an exoplanet researcher at the Space Telescope Science Institute and first author of the study, commented: "This analysis is also particularly interesting because you get three-dimensional information about the planet that was not available before. Because we can see that the edge is warmer at night, which means it is a little fluffier. So, in theory, there is a small expansion near the end of the night side of the planet."
Scientists discover information about exoplanet atmospheres by measuring the light the planet receives when it passes in front of its star. In this process, the star's light is changed as it is filtered through the planet's atmosphere. Instruments aboard the James Webb Space Telescope can detect these changes, with specific signatures revealing different molecules in the atmosphere.
However, this technique assumes that the atmosphere is roughly the same across the Earth's surface.
On WASP-39b, the dayside that always faces the star is much hotter than the nightside. Because of the way the planet spins, this huge temperature difference is thought to create a strong wind at the equator that moves in one direction. This forms the "Morning Breeze" and the "Evening Breeze". "Morning breeze" is the cool night wind blowing to the day side, while "evening breeze" is the hot daytime wind blowing to the night side. The data shows that evening temperatures are significantly higher, reaching a scorching 800°C (1500°F), while morning temperatures are relatively cooler at 600°C (1100°F).
Cloud formation is related to temperature, so the team expected the number of clouds to be different in the morning and evening. They tested this using several methods of analyzing JWST data and found that, as predicted, there were more clouds in the morning than in the evening.
Dr. Kirk developed one of the analysis techniques that focuses solely on the light received by the planet as it begins and ends across the star's surface. Since only the edges of the planet "touch" the star's disk at these moments, the star's light is only filtered through the morning or evening sides of the atmosphere, respectively. The results of the analysis fit well with other analyzes done by other members of the team, which includes researchers from the United States and Europe.
The team now hopes to expand their analysis to include data from more instruments on JWST. The telescope carries instruments that analyze light at a range of wavelengths, from visible to infrared, revealing more details about differences in WASP-39b's atmosphere.
Dr. Kirk said: "Now that we have demonstrated the feasibility of this method on JWST, and the very high accuracy of JWST, this really opens up a new way for us to understand and measure the atmospheric circulation of exoplanets, to which we have previously been largely insensitive."
Compiled from /ScitechDaily