Astronomers have identified the oldest asteroid families and, by process of elimination, the oldest intact asteroids in the main belt. A team including SwRI scientists developed a technique to identify ancient asteroid families that have drifted apart. Asteroid surfaces heat up during the day (as illustrated by this image) and cool down at night, giving off radiation that can act as a sort of mini-thruster. This force can cause asteroids to drift widely over time, making it difficult to identify families of fragments leftover after asteroid collisions eons ago.
Image Courtesy of NASA/GSFC