A fresh analysis of data from NASA's Voyager 2 flybys in 1986 and 1989 is challenging the long-held classification of Uranus and Neptune as 'ice giants.' Scientists now propose that the interiors of these distant worlds may instead consist of layered magma oceans beneath their hydrogen and helium atmospheres.
The conventional model assumed a thick mantle of water, methane, and ammonia ices. The new hypothesis draws on laboratory experiments simulating extreme pressures and temperatures, suggesting that these compounds would form a conductive, fluid layer of magma rather than a solid icy shell. This could explain the planets' unusual magnetic fields, which are offset and tilted relative to their rotation axes.
Voyager 2 remains the only spacecraft to have visited either world, leaving vast gaps in observational data. The study relies on theoretical models and high-pressure physics experiments, not direct measurements. Without a dedicated orbiter, the true composition remains speculative.
The findings have broader implications for exoplanet science. Many Neptune-sized worlds discovered around other stars are assumed to be ice giants; if the magma-ocean model holds, it would reshape our understanding of the internal dynamics and evolution of these common planets.
A dedicated mission to Uranus has been recommended by the 2023 Planetary Science Decadal Survey as a top priority, but no firm launch date has been set. Until such a mission flies, the debate between ice versus magma interiors will remain unresolved.