An artist’s rendition of a Neptune-like exoplanet. Photo Credit: NASA, ESA, CSA, R. Crawford (STScI) A Unique Laboratory for Alien Weather
Orbiting its host star in less than a day, LTT 9779 b is subjected to searing temperatures reaching almost 2,000°C on its dayside. The planet is tidally locked (similar to Earth’s Moon), meaning one side constantly faces its star while the other remains in perpetual darkness. Despite such extremes, Coulombe’s team discovered that the planet’s dayside hosts reflective clouds on its cooler western hemisphere, creating a striking contrast to the hotter eastern side. “This planet provides a unique laboratory to understand how clouds and the transport of heat interact in the atmospheres of highly irradiated worlds,” says Coulombe.
Using JWST, the team uncovered an asymmetry in the planet’s dayside reflectivity. Coulombe proposed that the uneven distribution of heat and clouds is driven by powerful winds that carry heat around the planet. These findings, published in Nature Astronomy help refine models describing how heat is transported across a planet and cloud formation in exoplanet atmospheres, helping to give us a better understanding of weather patterns.
Mapping the Atmosphere of an Ultra-Hot Neptune
To get their results, the researchers studied the atmosphere in detail by analyzing both the heat emitted by the planet and the light it reflects from its star. They discovered clouds made of materials like silicate minerals, which form on the slightly cooler western side of the planet’s dayside. These reflective clouds help explain why this planet is so bright at visible wavelengths, bouncing back much of the star’s light.
Then, by combining this reflected light with heat emissions, the team was able to create a detailed model of the planet’s atmosphere. Their findings reveal a delicate balance between intense heat from the star and the planet’s ability to redistribute energy. The study also detected water vapor in the atmosphere, providing important clues about the planet’s composition and the processes that govern its extreme environment.
“With these new kind of observations we’re starting to understand the physical processes driving the extreme weather patterns on these planets,” explains Professor Björn Benneke, a co-author of the study and Coulombe’s research advisor. “Previously we had always aimed to only observe the light thermally emitted by these planets with JWST, but here, we showed that we can also use JWST to observe the light that is being reflected by the clouds on these planet. .”
A Trailblazing Study with JWST
JWST has once again demonstrated its incredible power, allowing scientists to study the atmosphere of LTT 9779 b in unprecedented detail. For an exoplanet like LTT 9779 b, which is tidally locked to its star, the amount and type of light we observe changes as the planet rotates, showing us different parts of its surface. By capturing spectra at various phases, researchers can map out variations in temperature, composition, and even cloud coverage across the planet’s surface.
The study highlights the groundbreaking work that could not be done without the help of JWST. The telescope’s ability to observe exoplanets across a wide wavelength range allows scientists to disentangle the contributions of reflected light and thermal emission in ways never before seen. “This is just the beginning of what JWST is beginning to reveal about these fascinating worlds,” said Coulombe.