The TRAPPIST-1 system, which hosts seven temperate Earth-sized planets orbiting an ultracool red dwarf star, presents a significant opportunity for scientists to test theories regarding the composition, differentiation, and internal structure of exoplanets. A notable aspect of this system is the comparatively low bulk densities of its planets, which suggest the presence of substantial volatile materials or propose a scenario where the metallic core has been completely oxidized.
In a recent study, researchers applied an updated model for metal-silicate partitioning to analyze the differentiation processes of these planets. They discovered that during core-mantle differentiation, oxygen behaves more like a siderophile element—meaning it has an affinity for iron—resulting in larger planet radii. To fully oxidize the iron present in the core, substantial quantities of oxygen are required, particularly if these planets evolve from a composition similar to Earth.
The findings indicate that rocky planets lacking a core can reach up to approximately four Earth masses. This raises intriguing questions about the observed density deficits in the TRAPPIST-1 planets and potentially in other M dwarf systems, pending confirmation from future observations. The researchers propose that these anomalies could be attributed to the specific elemental compositions available during the formation of the planets, which are closely related to the metallicity of the host star.
Lead author Dongyang Huang and co-author Caroline Dorn emphasize the importance of understanding these processes to further elucidate the nature of planetary formation and differentiation in varying stellar environments.
