Lutetia, main-belt asteroid. These four images of this asteroid (formally known as 21 Lutetia) were obtained by the European Space Agency's Rosetta spacecraft. The images were obtained at the point of closest approach on 10 July 2010. This flyby took place during the spacecraft's flight to rendezvous with a comet in 2014. Lutetia is 4.5 billion years old, and formed during the early history of the solar system. It is 130 kilometres along its longest axis. Its exact composition is uncertain, as though it is classified as a metallic asteroid it is covered by a layer of regolith (loose rocks) and craters.