All asteroids are not created equal. However, some are so different from one another that they can be described as incredibly bizarre.
Kleopatra is an asteroid that hangs out in the Asteroid Belt between Mars, Jupiter and Earth. It has two lobes connected by a long neck, a morphology which earned it the nickname "dog bone-asteroid".
This strange-looking space rock has two small moons, AlexHelios, and CleoSelene. These are named after Cleopatra, the famous Egyptian Pharaoh.
Scientists have obtained the most detailed images yet of this amazing space anomaly. We have known about it for over two decades. These images are helping us to understand how Kleopatra formed. The results indicate that the moons were created from Kleopatra’s own material.
Franck Marchis, an astronomer at the SETI Institute and Laboratoire d'Astrophysique de Marseille, France said that "Kleopatra" is a truly unique body in the Solar System.
Science can make a lot more progress by studying strange outliers. Kleopatra, I believe, is one of these outliers. Understanding this complex, multiple-asteroid system can help us understand more about the Solar System.
Astronomers used new Kleopatra images to create more precise measurement constraints. They also developed a new 3D model and defined the orbits for CleoSelene and AlexHelios in two papers published in Astronomy & Astrophysics.
This work was done using observations made with the powerful SPHERE instrument that is attached to the European Southern Observatory’s Very Large Telescope in Chile. The researchers were able take images from various angles as Kleopatra travelled through space.
They were able to calculate that Kleopatra measures approximately 270 km (168 miles). One of the dumbbell lobes is larger than the other and that they are joined by a thick neck. Researchers were able to calculate Kleopatra’s volume using the newly-described dimensions.
(ESO/Vernazza Marchis et.al./MISTRAL algorithm[ONERA/CNRS]
Above: Kleopatra and AlexHelios with CleoSelene
The orbits of CleoSelene and AlexHelios were being constrained by a second team. This is crucial because orbits are limited by the gravitational fields they traverse, which correlates with the masses in this system.
Miroslav Bro, an astronomer at Charles University in Czechia, stated that "this had to be solved because if the orbits of the moons were wrong then everything was wrong including the mass of Kleopatra."
The team was able, using new observations and mathematical modeling, to accurately describe the orbits of the moons. This resulted in Kleopatra's new mass being calculated at 2.97 x 10018 kilograms. This is significantly lower than the previous calculations which gave 4.64 x 101 kilograms.
Once you know the mass and volume of an object you can calculate its density. Marchis and his collaborators used the data from Bro and his team to calculate the density of Cleopatra. The asteroid's density was very low, as Kleopatra is considered to be metal-rich.
This information can reveal a lot about the formation of Kleopatra. The asteroid's low density indicates that it is porous, a loose "rubble heap" of pieces of rock with very little hanging together. These rubble piles were formed by material being flung from a parent body in a massive impact. They then reassemble over time.
Kleopatra will barely hold its own together if it is porous. Rotation time for the asteroid is around 5.4 hours, which is faster than average. This is a very stable period. If it were to speed up, it would be ripped apart by the centripetal force.
This critical rotation state means that the effective gravity at the Equator is low. Material in this area could be being lifted away from the Asteroid.
This could be a clue to the formation of CleoSelene and AlexHelios if it is true. If Kleopatra is being ejected, then it could have formed the moons, making them the asteroid's kids.
These papers were published in Astronomy and Astrophysics. You can find them here and here.