The Dense, Rocky Core of Haumea Revealed by Satellite Dynamics

Icy dwarf planets in the outer solar system are among the most enigmatic known bodies, showing activity ranging from atmospheric resurfacing to possible cryovolcanism. Yet their interiors remain largely theoretical, with few empirical measurements to guide understanding. The orbits of their moons offer a way to break this deadlock, providing a direct probe of dwarf planet interiors.

To investigate Haumea's interior, the researchers fitted a new dynamical model to two decades of precise Hubble Space Telescope astrometry of its satellite system. This allowed them to simultaneously measure Haumea's dynamical oblateness, J2, and the masses of its satellites.

Combining the J2 measurement with occultation-derived shape models conclusively shows that Haumea has a dense rocky core overlaid with an ice-rich mantle. However, the current dataset is not constraining enough to fully determine the detailed internal structure, such as core and mantle densities or whether the interior is two-layer versus three-layer. The analysis does find a slight preference for models in which Haumea retains a frozen-in fossil figure, but more data are needed to statistically confirm this.

Future observations of the satellite system, as well as stellar occultations, are needed to fully test this hypothesis and should substantially tighten constraints on Haumea's interior. Taken together with other recent evidence for geophysical and geochemical evolution of dwarf planets, the work shows that dense rocky cores and subsurface oceans are likely to be ubiquitous among the trans-Neptunian dwarf planets.