The asteroid 216 Kleopatra has two lobes and a constricted middle, leading astronomers to liken it to a “dog bone.”
Researchers have conducted new observations of asteroid 216 Kleopatra using the Very Large Telescope of the European Southern Observatory (ESO) in Chile. The clarity of the images allows them to learn more about the mass and 3D shape of the asteroid. This information could shed light on the formation process of Kleopatra and its two accompanying moons. At its closest approach, Kleopatra flies about 200 million kilometers from Earth.
Comparison of the size of 216 Kleopatra with northern Italy. (Photo: ESO/M. Kornmesser/Marchis).
Two studies, including observations published on September 9 in the journal Astronomy & Astrophysics, focus on different aspects of Kleopatra. One study concentrates on the shape of Kleopatra, while the other examines the asteroid’s mass and its two moons. According to Franck Marchis, the lead researcher on the 3D shape study, Kleopatra is indeed a unique object in the Solar System. Understanding this complex asteroid system could help astronomers explore more about the Solar System.
Marchis is a planetary astronomer at the SETI Institute in Mountain View, California, and a member of the Astrophysical Laboratory in Marseille, France. The unusual-shaped asteroid Kleopatra resides in the asteroid belt between Mars and Jupiter, orbiting the Sun. Radar observations of Kleopatra from 20 years ago revealed its shape, consisting of two lobes connected by a constricted middle. In 2008, Marchis and colleagues discovered two small moons orbiting the asteroid, naming them AlexHelios and CleoSelene, after the children of the Egyptian queen Cleopatra.
The instruments of the Very Large Telescope captured images of Kleopatra from 2017 to 2019, allowing astronomers to observe Kleopatra and its moons from various angles to construct a 3D shape. The research team determined that one of the asteroid’s lobes is larger than the other. The object measures approximately 269 kilometers in length, roughly half the length of the English Channel. They also used observations to calculate the orbits of Kleopatra’s two moons.
The latest research on Kleopatra’s moons enables scientists to understand how the asteroid’s gravity affects the motion of its two moons. They were also able to calculate the asteroid’s mass, which was found to be 35% lower than previous estimates. The density of Kleopatra is less than half that of iron, indicating that, despite containing metal, it may be a porous rubble pile asteroid. This type of asteroid is a cluster of boulders held together by gravity, typically formed when debris re-accumulates after a significant impact, such as a collision with a larger asteroid.
Conclusively, Kleopatra is a rubble pile asteroid, which also explains why it has two moons. The asteroid spins so quickly that material can escape from its surface when Kleopatra collides with anything, even very small objects. Debris separated from Kleopatra in the past, forming the moons AlexHelios and CleoSelene. The upcoming Extremely Large Telescope from ESO, expected to begin operations in 2027, may provide even more detailed information about this peculiar asteroid.
