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Ceres is a dwarf planet in the main asteroid belt between Mars and Jupiter. Its comparatively rounded shape distinguishes its self-gravitating structure from many much smaller irregular asteroids; its location and dynamical context distinguish it from a major planet.

The Dawn spacecraft investigated its surface using imaging, spectroscopy and gravity measurements. Water-bearing minerals and bright salt-rich deposits provide evidence of chemical interaction with water. These observations constrain surface and near-surface processes, while any reconstruction of the deeper interior also requires a model; a bright deposit alone is not a complete map of an underground reservoir.^[ref]

The Dawn spacecraft was an orbital mission to Vesta and Ceres, two bodies in the main asteroid belt. Studying both with one instrument suite made their contrasting surfaces and internal evolution directly comparable. Its ion propulsion accelerated Xenon ions to provide a small thrust over long intervals, enabling prolonged orbital observations at two separate destinations.^[ref]

Its framing camera mapped landforms and surface textures; its visible/infrared spectrometer measured spectral features associated with surface minerals; and its gamma-ray and neutron detector constrained near-surface elemental composition. Radio tracking additionally constrained gravity through the spacecraft's orbital response.^[ref]

These instruments answer different questions. A bright patch in an image measures reflected light under a particular illumination geometry, not a unique composition. Combining spectral absorption features with imaging and nuclear-radiation measurements helps distinguish a compositional explanation from a change in grain size or viewing angle. The mission thus illustrates how complementary measurements make a geological inference more informative than a detailed photograph alone.

Vesta, formally numbered 4 Vesta, is a large asteroid in the main asteroid belt with a differentiated interior and basaltic crust. It preserves evidence that a small body could melt and separate into internal layers early in Solar-system history, making it a useful comparison with the larger terrestrial planets.^[ref]

The Dawn spacecraft mapped its surface and measured its reflected spectrum and gravitational field. Large impact basins expose material from beneath the original surface, while spectral measurements constrain mineral composition. Changes in the spacecraft's radio-tracked orbit constrain the distribution of mass. The inference of an interior structure combines these observations with physical models; a surface image alone cannot locate a buried core.

Basaltic meteorites provide a complementary laboratory record. Comparing their mineral signatures with remote spectra tests the connection between recovered rock samples and a parent body. Agreement is evidence about composition and origin, whereas reconstructing the body's full cooling and impact history requires additional geological constraints.