The asteroid Didymos and its smaller, satellite asteroid Dimorphos comprise a binary asteroid system within the solar system. Didymos was discovered in 1996, and is estimated to contain roughly 99% of the mass of the Didymos-Dimorphos system. Didymos' orbital location varies between Earth orbit and just outside Mars' orbit.
Didymos has a mass of 500 to 600 billion kilograms. It is roughly spherical in shape, with an approximate diameter of 780 meters (slightly less than half a mile), and rotates once about its axis about every 2.3 hours.
Didymos orbits the Sun in an elliptical orbit, with a nearest and farthest distance from the sun of about 1 AU and about 2.3 AU, respectively. It orbits the Sun every 2.1 years.