Exploring the Frontier of Sub-Neptune Exoplanets with JWST

What is it about?

This article is about new advances in the understanding of sub-Neptune exoplanets made possible by observations with the James Webb Space Telescope. Sub-Neptunes are planets with sizes and masses between those of Earth and Neptune. There are no such planets in the solar system but they form the large majority of exoplanets, i.e. planets orbiting other stars.

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Photo by NASA Hubble Space Telescope on Unsplash

Photo by NASA Hubble Space Telescope on Unsplash

Why is it important?

Sub-Neptunes are an exotic class of planets and can span a diverse range of interiors, atmospheres and formation histories. They can include a variety of planet types, from predominantly rocky gas dwarfs and smaller versions of Neptune ('mini-Neptunes') to water worlds with varied atmospheric compositions, with some potentially capable of harbouring habitable conditions. Sub-Neptunes are therefore a central focus in the study of planetary processes in low-mass exoplanets with many open questions. Pioneering JWST observations have led to detections of prominent molecules in several sub-Neptune atmospheres. The chemical abundances are providing initial insights into such planets, with important implications for their atmospheric diversity, internal structures, formation mechanisms, and habitability. These results set the stage for a generalised classification of such planets and offer an early panoramic view of this exotic frontier.