Didymos is a binary asteroid in solar orbit extending out beyond Mars. The primary mountain-sized body has a diameter of around 780 m and a rotation period of 2.26 hours. The secondary body, Dimorphos, has a diameter of around 151 m, similar to the Great Pyramid of Giza, and orbits the primary at a distance of around 1.1 km from the primary surface in around 11 hours and 22 minutes (reduced by 33 minutes after DART's impact).