The researchers used for their study zu Kleopatra das Very Large Telescope (VLT) in the Chilean Atacama Desert. There were between 2017 and 2019 with the instrument SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) recorded images that had never been seen before from this special asteroid. In this way, Cleopatra’s shape and mass could be determined much more precisely and new knowledge gathered about how the celestial body and its two moons came into being. “Cleopatra is really a unique object in our solar system,” emphasizes study director Franck Marchis.
Cleopatra orbits the sun in the asteroid belt between Mars and Jupiter. 20 years ago it was discovered by radar that the celestial body looks like a dog’s bone – with thickened ends and a thinner center piece. In 2008 Marchis and Co. were also able to determine that Cleopatra is orbited by two moons named after the children of the Egyptian Queen AlexHelios and CleoSelene. With the latest data obtained at the VLT, the researchers were able to determine the volume of the asteroid more precisely and calculate that it is around 270 kilometers long. That is about as long as the distance from Leipzig to Nuremberg.
In a second study, which was led by the Czech astronomer Miroslav Brož, the experts also tried to determine the orbits of the two Cleopatra moons. In earlier studies, the scientists were wrong with their estimates, now they were able to describe exactly how Cleopatra’s gravity influences the moons’ movements – and thus also the mass (35 percent less than in earlier estimates) and density (significantly less than assumed) a lot better determine. The researchers deduced from the low density of the asteroid that it resembles a loose “heap of rubble”, which was probably formed from recovered material after a gigantic impact.
These findings are particularly remarkable when you consider that Cleopatra is around 200 million kilometers from Earth. The apparent size in the sky corresponds to that of a golf ball about 40 kilometers away. The asteroid should be even better with the Extremely Large Telescope, which is currently under construction (ELT) can be observed. “I can hardly wait to point the ELT at Cleopatra to see whether there are more moons and to measure the lunar orbits so precisely that even small changes can be detected,” says Franck Marchis. By studying this asteroid, astronomers could also learn more about our solar system itself.