Olympus Mons, Mars. Artwork of the profile of Olympus Mons, the largest known volcano in the Solar System. It is found on Mars, the fourth planet in our Solar System. Its summit rises 27 kilometres (km) above the surrounding plains (Mount Everest is 8.8 km high), while the base measures 600km across, resulting in a gentle surface slope. Also visible is the cliff that marks the base of the slope. The rough, crinkly patchs around the volcano form the Olympus Mons Aureole. Both the Aureole and the basal cliff are poorly understood, although it is thought that their origins may be related.