Kleopatra
Key facts
- What it is
- Main-belt asteroid with two moons
- Size
- About 270 km long
- Discovered
- 1880, by Johann Palisa
- Spacecraft
- Not yet visited
- Orbit group
- Main-belt Asteroid
- Average distance from the Sun
- 2.8 au (about 420 million km)
- Time to go round the Sun
- 4.7 years
- Closest and farthest from the Sun
- 2.1 to 3.49 au
- Tilt of its orbit
- 13.1°
- Spins once every
- 5.4 hours
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.
Kleopatra is one of the strangest shapes in the asteroid belt. Radar observations in 2000 showed that it is long and narrow with swollen ends, and it has been called the dog-bone asteroid ever since. From end to end it measures about 270 kilometres, while its middle is much slimmer.
It was discovered in 1880 by Johann Palisa, an Austrian astronomer who found more than a hundred asteroids. Kleopatra is an M-type asteroid, so its surface seems to contain a good deal of metal, and it reflects radar strongly. Yet its overall density is fairly low. The likely explanation is that Kleopatra is a rubble pile: a loose heap of fragments held together by gravity, with plenty of empty space between them, rather than a single solid lump.
In 2008 astronomers found that Kleopatra has two small moons, later named Alexhelios and Cleoselene after the twin children of the Egyptian queen Cleopatra. Each is only a few kilometres across. The moons are very useful, because the time they take to circle Kleopatra reveals its mass. Combined with its size, that gives the density that points to its rubbly interior.
How such a shape forms is still debated. Kleopatra spins once roughly every five and a half hours, quite fast for its size, and it may be close to the speed at which loose material would start to fly off its ends. The moons may even be pieces that escaped this way. Kleopatra shows how collisions and spin can sculpt an asteroid into almost any form.