Constraints on the internal mass distribution of asteroid (101955) Bennu from OSIRIS-REx mission data
Ashish A. Cavale, Daniel J. Scheeres
Icarus
Available online 14 July 2026, 117260
“Highlights
- Iterative constrained least-squares estimation of a heterogeneous density model of Bennu.
- Computed model matches targeted OSIRIS-REx gravity coefficients, including all degree 1 and 2 terms and the degree 3 and 4 zonals.
- Solution favors previous analytical findings of an under-dense core and equatorial torus.
- Fitting additional higher order gravity coefficients requires additional heterogeneous components.”
“The OSIRIS–REx mission provided the first measured gravity field of a sub-kilometer asteroid, enabling constraints on the internal mass distribution of the rubble-pile asteroid (101955) Bennu. In this work, Bennu is represented as a constant-density body based on the shape model with a set of superimposed polyhedral components that capture deviations from constant-density. Component relative densities and the inner-core position are estimated using an iterative, constrained, weighted least–squares formulation that enforces global mass conservation and targets a set of gravity coefficients. The results are consistent with earlier analyses of Bennu’s density distribution while accounting for a more complex gravity field, and thus provide a more precise model. The solution produces a gravity field that reproduces the set of targeted measured gravity coefficients, including the degree 1 and 2 terms and the degree 3 and 4 zonal coefficients. The estimated model produces an under-dense inner core and under-dense equatorial torus, balanced by a prescribed over-dense subsurface layer and under-dense surface layer based on visual observations and analysis. Additional components in the form of regional mass concentrations are required to reproduce higher degree and order gravity coefficients. Although the resulting configuration is not unique, the results demonstrate that Bennu’s measured gravity field can be produced using a minimal set of physically motivated components, providing a framework for constructing possible internal density distributions consistent with the measured gravity field.”
