Horizontal quenching explains missing methane in the atmosphere of planet WASP-43 b

Star system: WASP-43 | Distance from the Sun: 284 light years

WASP-43 b is a hot Jupiter—a gas giant planet orbiting extremely close to its parent star. By using sophisticated three-dimensional computer simulations to analyze data from the James Webb Space Telescope, researchers have modeled the complex chemistry of the planet's atmosphere. The study focused on understanding how atmospheric circulation and chemical reactions influence the distribution of gases across the planet's day and night sides.

The simulations demonstrate that a process called horizontal quenching is the primary cause for the lack of detectable methane on the planet's night side. This occurs when strong wind jets, moving faster than 500 meters per second, rapidly transport atmospheric gases across the planet before they can reach chemical equilibrium. Additionally, the research incorporated carbon-sulfur chemical interactions, which further reduce expected methane levels.

While water, carbon monoxide, and carbon dioxide were consistently modeled, other chemicals proved highly sensitive to specific model assumptions. The team also examined the possibility of high atmospheric metallicity—an abundance of elements heavier than hydrogen and helium. They concluded that a high-metallicity atmosphere is unlikely, as it would have produced detectable sulfur dioxide signatures that were not observed in the telescope data.

Key findings
- Horizontal quenching by fast wind jets effectively removes methane from the night side of WASP-43 b.
- Coupled carbon-sulfur chemistry is essential for accurately modeling methane depletion.
- High atmospheric metallicity is ruled out because it would have resulted in observable sulfur dioxide features.
- Pole-to-equator circulation increases ammonia and hydrogen cyanide levels, though these changes remain below current detection limits.
- Water, carbon monoxide, and carbon dioxide are the most robustly modeled atmospheric components.

Scientific study

Phase-dependent chemistry of WASP-43 b revealed with a suite of one-, two-, and three-dimensional models (external link)