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A Small Solar System body is an object orbiting the Sun that is neither a planet nor a dwarf planet nor a natural satellite, in the classification adopted by the International Astronomical Union in 2006. The category includes most asteroids, most trans-Neptunian objects and comets. The definition is tied to the Solar system; it is not a general classification of every small astronomical object.^[ref]

The categories encode physical distinctions. A dwarf planet has enough self-gravity to assume a nearly round equilibrium figure but has not cleared its orbital neighborhood. A Small Solar System body does not satisfy both planetary shape and orbital-clearing conditions. A natural satellite is classified separately even if it is small and irregular.

For example, Ceres lies in the asteroid belt but is a dwarf planet, whereas Vesta is classified as an asteroid. Merely being in the asteroid belt therefore does not determine which formal category an object occupies.^[ref][ref]

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.