NASA Jmaes Webb Telescope reveals secrets of mysterious Sub-Neptune exoplanet

This artist’s concept shows what the hot sub-Neptune exoplanet TOI-421 b could look like. It is based on spectroscopic data gathered by Webb, as well as previous observations from other telescopes on the ground and in space. (Image: NASA)

In a groundbreaking step for exoplanet science, NASA's James Webb Space Telescope (JWST) has given us an unprecedented look at the atmosphere of TOI-421 b, a sub-Neptune exoplanet about 245 light-years from Earth in the constellation Lepus. This sighting represents a major leap forward in our knowledge of these common but mysterious celestial objects.

A Clearer View of Sub-Neptunes

Sub-Neptunes, planets with diameters bigger than Earth's but smaller than Neptune's, are the most prevalent form of exoplanet found in our galaxy. Despite their prevalence, their atmospheric properties have been generally elusive because widespread clouds and hazes block spectral readings.

Yet, TOI-421 b breaks the pattern. Orbits a Sun-like star and has an atmospheric temperature of about 1,340°F (727°C), putting it far higher than the 1,070°F boundary predicted by scientists for the formation of methane-induced hazes. Lack of such hazes in the atmosphere of TOI-421 b has enabled JWST to record a clear transmission spectrum, yielding strong chemical signatures.

Revealing Atmospheric Composition

The JWST observations found water vapor in the atmosphere of TOI-421 b, as well as tentative evidence for carbon monoxide and sulfur dioxide. Significantly, methane and carbon dioxide, ubiquitous in the atmospheres of many planets, were not present. The data also indicate a hydrogen-rich atmosphere, an unexpected finding that contradicts earlier assumptions regarding sub-Neptune compositions.

Dr. Eliza Kempton, University of Maryland principal investigator, was thrilled: "By examining their atmospheres, we're learning more about how sub-Neptunes formed and evolved, and part of it is learning why they don't occur in our solar system."

Implications for Planetary Science

The transparent atmosphere of TOI-421 b presents a rare chance to observe sub-Neptunes free from the contamination of atmospheric hazes. This fact not only allows us to better understand the composition of these planets but also gives us clues about their formation and evolution. The results indicate that TOI-421 b might have formed in a different way than its cooler siblings, perhaps preserving a more primordial atmosphere like that of its host star.

As JWST continues to study other sub-Neptunes, researchers hope to establish if TOI-421 b is an exception or indicative of a widespread group of haze-free, hydrogen-rich planets. This study opens the door to a greater understanding of planetary diversity in the universe.