Stellar flares explain missing methane in the atmosphere of exoplanet V1298 Tauri b

Star system: V1298 Tauri A | Distance from the Sun: 352 light years

The young exoplanet V1298 Tauri b is a warm sub-Neptune orbiting a very young orange dwarf star. Recent observations from the James Webb Space Telescope have revealed an atmospheric mystery: the planet contains far less methane than expected, while showing surprising levels of carbon dioxide. This phenomenon, known as the missing methane problem, has been observed in several cool planets, where standard chemical models fail to predict the observed composition.

To explain this depletion, previous theories suggested the planet might have an extremely hot interior that mixes gases to the surface. However, such high internal temperatures are inconsistent with the planet's young age and small size. The new findings offer a different solution, suggesting that frequent, intense bursts of energy from its host star—known as stellar flares—are responsible for breaking down methane in the planet's upper atmosphere.

During a stellar flare, high-energy light destroys methane molecules faster than they can be replenished by the upward movement of gas from deeper layers. Because the young star flares so frequently, the atmosphere never has enough time to recover, maintaining a steady state of low methane and high levels of carbon monoxide, carbon dioxide, and hydrogen cyanide. This model successfully recreates the features observed in the planet's transmission spectra.

Key findings
- V1298 Tauri b shows unexpected methane depletion and high abundances of carbon dioxide.
- High internal heat is unlikely to be the cause of methane loss due to the planet's young age.
- Frequent stellar flares drive methane destruction through a process called photolysis.
- Atmospheric gas diffusion is too slow to replace methane between flare events.
- Synthetic spectra based on flare-driven chemistry match recent telescope observations.

Scientific study

Stellar Flares Rather than High Tint As Possible Cause for the Missing Methane in Young Exoplanets: The Case Study of V1298~Tau\,b (external link)