| Object type | Main-belt asteroid, Tholen M-type / SMASS Xe[1] |
|---|---|
| Discovered | April 10, 1880 by Johann Palisa at Pola (now Pula, Croatia)[2] |
| Named for | Cleopatra VII of Egypt[2] |
| Dimensions | ≈ 276 × 94 × 78 km[1] |
| Mean diameter | ≈ 120–122 km (volume-equivalent)[2] |
| Mass | (2.97 ± 0.32) × 10¹⁸ kg[2] |
| Density | 3.38 ± 0.50 g/cm³[2] |
| Rotation period | ≈ 5.39 hours[1] |
| Moons | Alexhelios (≈ 8.9 km, 2.7 d) and Cleoselene (≈ 6.9 km, 1.8 d)[2] |
| Distance from Sun | 2.10–3.49 AU[1] |
| Orbital period | ≈ 4.7 years[1] |
| Inclination | ≈ 13.1°[1] |
The dog-bone asteroid
Kleopatra is one of the strangest-looking objects in the asteroid belt: about 276 km long but under 100 km wide, with two lobes joined by a thinner middle.[1] Its volume-equivalent diameter is only about 120 km.[2]
The elongation first showed up in a 1991 stellar occultation timed from eight locations. Later radar observations at Arecibo showed the two lobes are connected, like a ham-bone, and the resulting shape model made the cover of Science.[2][5]
Alexhelios and Cleoselene
A 1988 search for moons came up empty. Then in September 2008, Franck Marchis and colleagues announced two moons found with the Keck Observatory’s adaptive optics.[2]
In 2011 they were named after Cleopatra’s twin children: Alexhelios (outer, about 8.9 km, 2.7-day orbit) and Cleoselene (inner, about 6.9 km, 1.8-day orbit).[2]
Metal — but how much?
Kleopatra is an M-type asteroid, a class often linked to metal.[4] Its moons allow its mass to be measured: (2.97 ± 0.32) × 1018 kg, lower than earlier thought, and a bulk density of 3.38 ± 0.50 g/cm³.[2]
That density questions the old picture of a pure metal body. Radar suggests metal-rich material in the south but more ordinary rock along the equator. One explanation is a porous rubble pile with a lot of metal mixed in.[2][6]
Spun into shape
One idea explains shape, spin and moons at once: an oblique impact, perhaps 100 million years ago, spun Kleopatra up, stretched it out and flung off Alexhelios; Cleoselene may have split off around 10 million years ago.[2]
Kleopatra is a contact binary — if it spun much faster, the two lobes would separate and become a true binary system.[2][7]
Orbit
Kleopatra belongs to the background population of the central belt rather than any family. It orbits between about 2.1 and 3.5 AU every 4.7 years, tilted 13°.[2][1]
Holding a piece of an asteroid
No meteorite is known to come from Kleopatra, but iron and stony-iron meteorites do come from metal-rich asteroids. Our meteorite buying guide explains the main types and how to buy a genuine specimen.[4]
Read more
How Kleopatra got its dog-bone shape
From a 1991 occultation to Arecibo radar and adaptive optics — and a theory linking its shape, spin and moons.
Read →Alexhelios and Cleoselene: Kleopatra’s twins
Two small moons discovered with Keck in 2008 and named after Cleopatra’s children.
Read →Is Kleopatra made of metal?
Radar, density and spectra give mixed answers about one of the best-known M-type asteroids.
Read →Sources
- Small-Body Database Lookup: 216 Kleopatra — NASA JPL Solar System Dynamics
- 216 Kleopatra — Wikipedia
- Johann Palisa — Wikipedia
- M-type asteroid — Wikipedia
- Arecibo Telescope — Wikipedia
- Rubble pile — Wikipedia
- Contact binary (small Solar System body) — Wikipedia
- Occultation — Wikipedia
- Small-Body Database Lookup: 16 Psyche — NASA JPL Solar System Dynamics
- Planetary Fact Sheet (orbit comparison) — NASA NSSDCA
Figures are rounded; where sources differ we note it. Spotted an error? Tell us.