Sub-Neptunes are the most common type of planet in the galaxy but are absent in our solar system, making them intriguing. Scientists are especially interested in temperate sub-Neptunes, as some might be habitable.
In the habitable zone, these planets were believed to be massive ocean worlds with hydrogen-rich atmospheres, known as “Hycean” worlds, like K2-18 b. However, JWST data on TOI-270 d suggests a simpler explanation: a rocky super-Earth interior covered by a thick, hot atmosphere fits better.
TOI-270 d, located just 73 light years away, could be key to understanding a new class of planets. A study revealed it may be a giant rocky planet with a thick, hot atmosphere. NASA’s JWST detected gases suggesting extreme temperatures exceeding 1,000°F, hotter than Venus.
The geochemical model shows how gases equilibrate at these high temperatures before rising to levels detectable by the telescope, offering crucial insights into its atmosphere.
NASA’s TESS discovered three new planets nearby, including temperate ‘sub-Neptune’
TOI-270 d is likely not habitable but provides valuable insights into planetary origins and evolution. Researchers explain ammonia depletion through processes like high-temperature nitrogen gas production and its dissolution into a molten rock ocean.
They also determined that the planet is probably nitrogen-poor, as its building materials, such as chondritic meteorites, typically lack nitrogen. This discovery deepens our understanding of how planets develop in diverse environments.
The study shows that exoplanetary geochemistry has advanced to match the sophistication of studies within our solar system. Tools used to analyze planetary atmospheres here can now be applied to exoplanets, offering valuable insights into their temperatures, possible magma oceans, and the origins of their atmospheres.
Journal Reference:
- Christopher R. Glein, Xinting Yu, Cindy N. Luu. Deciphering Sub-Neptune Atmospheres: New Insights from Geochemical Models of TOI-270 d. Astrophysical Journal (submitted to arXiv), 2025 DOI: 10.48550/arXiv.2504.09752
Source: Tech Explorist
