Animation of the large asteroid 21 Lutetia. Lutetia is a main belt asteroid, orbiting the Sun between Mars and Jupiter, taking some 3.8 years to complete an orbit. It is irregular in shape, with its longest axis some 120 kilometres long, and its shortest around 75km. It is very dense for an asteroid, implying it is made of metal-rich rock, and the presence of hundreds of impact craters is testament to its strength.