Sub-Neptune planets are often covered in thick haze, making studying hard. However, NASA’s James Webb Space Telescope is changing that by observing TOI-421 b, an exoplanet once thought to be haze-free.
Earlier research suggested that planets hotter than 1,070°F might have less haze because they lack methane, which triggers haze-forming reactions. Scientists believed cooler planets had haze due to sunlight interacting with methane gas. Since hotter planets shouldn’t have methane, they were expected to be clearer.
TOI-421 b, a scorching 1,340°F exoplanet, was expected to have a clear atmosphere, and NASA’s Webb Telescope confirmed it!
By analyzing its atmosphere, scientists detected water vapor and signs of carbon monoxide and sulfur dioxide. However, methane and carbon dioxide were absent, reinforcing theories that hotter planets lack methane-driven haze.
A team discovered a sub-Neptune exoplanet orbiting a red dwarf star
The biggest surprise? A lightweight hydrogen atmosphere! Previous sub-Neptunes observed by Webb had atmospheres rich in heavier molecules, so this finding suggests TOI-421 b may have formed differently from cooler sub-Neptunes.
TOI-421 b’s hydrogen-rich atmosphere closely resembles its host star’s composition, making it more similar to giant planets in our solar system rather than other sub-Neptunes observed with Webb. This challenges previous expectations and suggests a different evolutionary path.
Unlike most sub-Neptunes, which typically orbit cooler red dwarf stars, TOI-421 b circles a Sun-like star, adding another layer to its uniqueness. Scientists now wonder—is TOI-421 b part of a larger pattern for hot sub-Neptunes around Sun-like stars, or just an anomaly?
To answer that, researchers plan to study more hot sub-Neptunes, hoping to unlock deeper insights into how these mysterious worlds form and evolve.
The team’s findings appear on May 5 in the Astrophysical Journal Letters.
