91 Aegina (from Latin Aegīna, Aegīnēta)[4] is a large main-belt asteroid.

The orbit of this object brings it to within 4.9 Gm of the dwarf planet Ceres, and the resulting gravitational interaction has been used to produce mass estimates of the latter.

[5] The cross-section size of the asteroid is 110 km and it has a rotation period of six hours.

The surface coloring of 91 Aegina is very dark and this C-type asteroid has probably a primitive carbonaceous composition.

Observation of absorption bands at wavelengths of 0.7 and 3μm indicate the presence of hydrated minerals and/or ice grains on the surface.