Hot Sub-Neptune Exoplanet Illustration

This artist’s concept shows what the hot sub-Neptune exoplanet TOI-421 b could look like.

TOI-421 b orbits a Sun-like star roughly 244 light-years from Earth in the constellation Lepus (the Hare). The planet is in between Earth and Neptune in terms of size, mass, and density, and its star is slightly smaller and cooler than the Sun. However, because the planet orbits extremely close to the star (just 0.056 astronomical units, or 5.6% of the distance between Earth and the Sun), it is very hot.

Spectroscopic observations of TOI-421 b captured by NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near Infrared Spectrograph) on NASA’s James Webb Space Telescope show strong evidence for water (H2O) and the possible presence of sulfur dioxide (SO2) and carbon monoxide (CO) in the planet’s hydrogen-rich atmosphere. Unlike cooler sub-Neptunes, TOI-421 b appears to have a clear atmosphere that is not shrouded in clouds and haze.

This artist’s concept is based on spectroscopic data gathered by Webb, as well as previous observations from other telescopes on the ground and in space. Webb has not captured any images of the planet.