A new model developed by researchers at the University of California, Santa Cruz, aims to demystify the “steam worlds” found beyond our solar system. These planets, known as sub-Neptunes, have a water-rich interior but are too hot to support liquid water on their surface. Instead, they develop thick steam atmospheres and layers of exotic phases of water that behave like neither gas nor liquid.
The model, led by postdoctoral researcher Artem Aguichine, helps scientists understand the composition and evolution of these steam worlds. By accounting for experimental data on the physics of water under extreme conditions, the team’s work advances theoretical modeling and sheds light on how these planets formed.
Sub-Neptunes are vastly different from icy moons like Europa and Enceladus in our solar system. While they orbit much closer to their stars, sub-Neptunes develop steam atmospheres and layers of supercritical water, a phase that has been produced in laboratories and is thought to exist in the deep interiors of Uranus and Neptune.
The new model enables scientists to trace the distribution of water during planetary system formation and understand its properties, which are essential for predicting the existence of life on these planets. The team’s work also highlights the importance of modeling the evolution of steam worlds over millions and billions of years.
With observations from the James Webb Space Telescope (JWST) and future missions like the European Space Agency’s PLAnetary Transit and Oscillation (PLATO) telescope, scientists will soon put this model to the test. The research aims to refine our understanding of these enigmatic planets and potentially uncover new niches for life in the galaxy.
DOI: 10.3847/1538-4357/add935
Source: https://phys.org/news/2025-08-aims-demystify-steam-worlds-solar.html