By studying the craters on asteroid Bennu, scientists can estimate how long it has been orbiting near Earth. Bennu is a carbonaceous asteroid that is about 500 meters in diameter. It is currently orbiting the Sun in the inner asteroid belt, between Mars and Jupiter. Bennu is thought to have originated in the outer asteroid belt, and it is believed that it was perturbed into its current orbit by the gravitational influence of Jupiter.

The surface of Bennu is covered in craters, which are formed when objects impact the asteroid. The size and frequency of craters can be used to estimate the age of the surface. Scientists have found that Bennu's surface is relatively young, with most craters being less than a billion years old. This suggests that Bennu has been orbiting near Earth for less than a billion years.

The presence of young craters on Bennu's surface also suggests that the asteroid is actively being bombarded by objects from space. This bombardment is likely due to Bennu's proximity to Earth, which is a major source of debris. The bombardment of Bennu by space debris could potentially alter its orbit over time, and it could eventually cause the asteroid to collide with Earth.

The study of craters on Bennu is helping scientists to better understand the history of the asteroid and its potential impact hazard to Earth. By understanding the age of Bennu's surface, scientists can estimate how long it has been orbiting near Earth and how likely it is to collide with our planet.