Dinkinesh
Key facts
- What it is
- Small main-belt asteroid with a moon
- Size
- About 790 m across
- Discovered
- 1999
- Spacecraft
- Lucy fly-by, 2023
- Orbit group
- Main-belt Asteroid
- Average distance from the Sun
- 2.19 au (about 330 million km)
- Time to go round the Sun
- 3.3 years
- Closest and farthest from the Sun
- 1.94 to 2.44 au
- Tilt of its orbit
- 2.1°
- Spins once every
- 2.2 days
An au (astronomical unit) is Earth's average distance from the Sun, about 150 million km. Orbit figures are from open tracking data, figures last updated 1 Nov 2026.
Dinkinesh is a small asteroid that was added to NASA's Lucy mission almost as an afterthought, and then produced one of its biggest surprises. Lucy flew past it on 1 November 2023, as a test of the system that keeps the spacecraft's cameras pointed at a fast-moving target.
The test worked, and the images showed that Dinkinesh, only about 790 metres across, has a moon. Even more unexpected, the moon, named Selam, turned out to be a contact binary: two rounded lobes, each roughly 200 metres across, resting against each other. It was the first time a contact binary had ever been seen orbiting another asteroid.
Dinkinesh itself has a ridge running around its middle and a long trough, signs that it is a rubble pile whose shape has been reworked over time. A likely story is that sunlight gradually sped up its spin, loose material moved towards the equator and some of it was flung into orbit, where it gathered to form the moon.
The names have a link to the mission's theme. Lucy is named after the famous fossil of a human ancestor found in Ethiopia in 1974. Dinkinesh is the name that fossil is known by in Ethiopia, meaning "you are marvellous" in Amharic, and Selam is the nickname of another fossil child found in the same region, meaning "peace".
Dinkinesh shows how much remains to be learned even about tiny asteroids, and how double and multiple systems form among them.