Asteroids are laboratories that astronomers can use to study the history of our Solar System. They provide a means to understand the current environment as well: since they have no atmosphere and (in most cases) relatively little mass, they are good proxies for what interplanetary spacecraft will experience on longer trips, such as missions to Mars.
The Hayabusa mission, conducted by the Japan Aerospace Exploration Agency (JAXA), traveled to the near-Earth asteroid known as Itokawa. The probe collected samples from the surface and returned them to Earth for analysis. As reported by Eizo Nakamura et al. in PNAS, Haybusa's samples showed the effects of the interplanetary environment, especially signs of impacts from tiny rocky particles. As a result, the JAXA scientists were able to piece together the impact history of Itokawa, showing that that the asteroid had survived and been shaped by collisions with objects ranging in size from 10 kilometers down to a nanometer.