A partially differentiated interior for (1) Ceres deduced from its gravity field and shape

Area of Science:

• * Planetary Science
• * Asteroid Science
• * Geophysics

Background:

• * Remote observations provided approximate density and shape of asteroid (1) Ceres.
• * Previous models ranged from homogeneous to fully differentiated interiors.
• * A key missing parameter, moment of inertia, constrained interior models.

Purpose of the Study:

• * To measure Ceres's gravity variation and moment of inertia.
• * To constrain models of Ceres's internal structure.
• * To understand the thermal and compositional evolution of Ceres.

Main Methods:

• * Obtained gravity and shape measurements using the Dawn spacecraft.
• * Analyzed data to determine hydrostatic equilibrium and moment of inertia.
• * Modeled interior structure using a two-layer model.

Main Results:

• * Ceres is in hydrostatic equilibrium with a normalized mean moment of inertia of 0.37.
• * Ceres is partially differentiated: a rocky core with a volatile-rich outer shell.
• * Gravity signal suppression indicates isostatic compensation, suggesting a low-viscosity layer at depth.
• * Outer shell thickness is 70–190 km, with density indicating a mix of volatiles and rock.

Conclusions:

• * Ceres's interior evolved thermally, but its differentiation is more complex than expected for its size.
• * The presence of a low-viscosity layer points to a thermal gradient rather than compositional.
• * Findings challenge simple models for mid-sized, ice-rich rocky bodies.