Dayside atmosphere of ultra-hot Jupiter WASP-178 b shows thermal inversion and neutral iron

Star system: HD 134004 | Distance from the Sun: 1362 light years

WASP-178 b is an ultra-hot Jupiter, a gas giant planet that orbits extremely close to its parent star, resulting in scorching atmospheric temperatures. New high-resolution optical observations of the planet’s dayside reveal a thermal inversion, a state where the temperature in the upper atmosphere increases with altitude, opposite to the expected cooling trend. These findings help clarify the complex, three-dimensional processes driving extreme weather on such worlds.

To study the atmosphere, the Gemini High-resolution Optical SpecTrograph (GHOST) at the Gemini South Observatory analyzed light emitted from the planet before and after it passed behind its host star. By using a technique called Doppler cross-correlation—which identifies the specific chemical signatures of elements based on how they shift their light due to the planet's motion—the researchers were able to confirm the presence of neutral iron.

Beyond iron, the data provided tentative evidence for the presence of neutral silicon and calcium in the dayside atmosphere. While models suggest many other elements may be too difficult to detect given current limitations, these observations provide a crucial data point for comparing WASP-178b to other ultra-hot Jupiters, refining our understanding of how high-energy radiation interacts with giant planet atmospheres.

Key findings
- Detection of neutral iron emission confirms a thermal inversion in the dayside atmosphere.
- Observations were captured in the optical spectrum using the GHOST instrument.
- Tentative signatures of neutral silicon and calcium were identified.
- Results support 3D atmospheric process models for ultra-hot gas giants.

Scientific study

High-Resolution Dayside Spectroscopy of the Ultra-Hot Jupiter WASP-178b with GHOST/Gemini South (external link)