The above images show that the asteroid is dominated by a large crater with a diameter of around 2 kilometres, but appears to have 23 craters that are more than 200 metres across. Asteroids will have formed in the early Solar System when tiny particles of dust and metal underwent sticky collisions with each other and gradually formed larger objects. Most of these asteroids will have eventually collided with, and helped to form, one of the planets, but millions still wander the Solar System - most beyond the orbit of Neptune.
The recent fly-by saw the spacecraft pass within 800 kilometres (500 miles) of the asteroid's surface at a speed of 31,000 kilometres per hour (19,200 miles per hour). The main purpose of the Rosetta mission is to rendevous with Comet 67 P/Churyumov-Gerasimenko in 2015. On arrival at 67P, Rosetta will enter orbit around the comet and stay with it as it journeys in towards the Sun. However, en route, Rosetta will pass 2 asteroids: 2867 Steins (in 2008) and 21 Lutetia (in 2010).
For more information about the ESA Rosetts Mission, click here.