Modeling Carbon-Based Planets with MAGRATHEA

A planet’s interior structure not only influences its habitability, but it also provides information about the planet’s formation and history. In the quest to characterize the variety of planetary discoveries, the most common practice is to rely on our understanding of the Earth’s differentiated interior structure, with an iron core and silicate mantle as a starting point. However, recent work by C. J. Shakespeare et al. (2025) shows that these assumptions may not be true for all planetary systems as the composition of the condensed material can change drastically towards a carbon mantle instead of a silicate one, once the C/O ratio of the system approaches and exceeds \(\sim 0.9\). In an effort to more fully understand the range of possible planetary bodies, we added the ability to model carbon-based mantles to our open-source planetary interior solver, MAGRATHEA. The newly added carbon mantle includes three relevant allotropes of carbon: graphite, diamond, and BC8 (body centered cubic with eight atoms per cell).