Eros appears to be a single solid, homogenous mass of silicate rock similar in composition to chondrite meteorites. The fact that it is homogeneous (no blobs of dense material like metal in its interior) suggests that this asteroid has never undergone differentiation to form a core-mantle-crust system. The irregular shape suggests that it was once part of a large body that was blasted apart by a collision at some time in the distant past.

The surface is covered with a layer of broken up rock (regolith) ranging in size from powder to 100-meter boulders (photo above). In places this 'soft' layer may be as thick as a 10-story building! Large craters are abundant, but small ones are much less common than expected (small impacts should be more common than large ones). The ubiquitous regolith (weathered debris) suggests that the asteroid is subject to considerable erosion, probably caused by the billions of years of many small impacts that have pelted the surface.

Some of the crater bottoms are covered in flat deposits of fine material (lower left above). On Earth, water creates such deposits when a stream dumps sediments into a lake, for example. Water has probably never been present on this asteroid, so how sediment was deposited in these basins is a bit of a mystery. It is possible that large impacts cause the asteroid to vibrate (like the Earth's surface does during an earthquake) and that this shaking causes sediment to move downslope and level out in basins. Cool.