The Japanese asteroid probe Hayabusa was sent to an asteroid called 25143 Itokawa years ago. It was recovered in June of 2010. The probe returned more than 1500 microscopic grains of dust that are currently being investigated to learn all that can be learned about asteroids and what the conditions on an asteroid are like. Scientists studying these dust grains retrieved from the asteroid had been able to confirm some new findings.
The new findings indicate that the asteroids are constantly reshaped by continual microscopic impacts for very high-speed objects such as tiny asteroids and other debris. The scientists have been looking at the size, mineralogy, shape, and geochemistry of five different grains of dust that were recovered by the probe. The smallest of the samples the team is working with measures a scant 40 microns. That is less than half the width of a human hair.
The surface of these grains were covered in tiny fractures suggesting shocks from impacts to the asteroid. The specks of dust also had a number of even smaller particles attached to it that were several microns wide or smaller. The pitted surfaces of the grains returned by the probe suggest that they were formed by micrometeorites just nanometers wide colliding with the asteroid. Despite the tiny size of these micro asteroids, the impacts were still high energy due to the velocity in the area of 11,200 to 22,400 mph.