“Cleopatra is truly unique in the solar system,” said Franck Marchis of the SETI Institute in California and the Astrophysics Laboratory in Marseille, head of research on the asteroid with its unusual shape and two moons, published in Astronomy & Astrophysics.
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“Thanks to the study of objects completely deviating from the series, science is making great progress. I think Cleopatra is one such body. By understanding this complicated system, we can learn a lot about the solar system, “he added.
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Cleopatra orbits the Sun in the so-called main belt of asteroids between Mars and Jupiter. According to Pavel Suchan from the Astronomical Institute of the Academy of Sciences of the Czech Republic, astronomers have referred to it as “a bone for a dog” since its unusual shape, ie a pair of lobes connected by a thick neck, was discovered on the basis of radar observations about 20 years ago.
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The processed image uses data from July 2017 and captures the asteroid Cleopatra (middle of the image) and both of its moons Alex Helios and CleoSelene (top right and bottom left).
Photo: ESO / Vernazza, Marchis et al./MISTRAL algorithm (ONERA / CNRS)
In 2008, Marchis and his colleagues discovered a pair of small bodies orbiting Cleopatra – the moons were named after the children of the famous Egyptian queen, Alex Helios and CleoSelene.
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The size of an asteroid? 270 km
To learn even more about the Cleopatra asteroid, scientists used images of the asteroid taken between 2017 and 2019 – now published – using the SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch), which works on the ESO / VLT (Very Large Telescope) telescope. ) in the Chilean Atacama Desert.
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Thanks to the rotation of the asteroid, astronomers were able to observe the body from different angles. They were thus able to create the most accurate 3D model of the shape of an object so far and specify its volume. They found that one of the lobes was slightly larger than the other. They set the length of the asteroid at 270 kilometers.
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In the second study, according to a report from ESO, a team led by Miroslav Brož from the Faculty of Mathematics and Physics at Charles University described how they used data obtained by the SPHERE instrument to refine the orbits of both asteroid moons. Although previous work has reported possible orbital parameters, new observations from the ESO / VLT telescope have shown that the moons are located elsewhere than at the predicted positions.
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“It simply came to our notice then. Because if the orbits of the moons are wrong, everything is wrong, including the weight of Cleopatra, “said Brož.
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Comparison of the size of the asteroid Cleopatra with northern Italy
Photo: ESO / M. Kornmesser / Marchis et al.
Thanks to new observations and models, it was possible to describe how Cleopatra’s gravity affects the motion of the moons and to determine their complicated orbits. The researchers were able to calculate the mass of the asteroid, which is 35 percent smaller than originally estimated.
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Did Cleopatra “give birth” to her moon?
Combining the newly determined volume and mass allowed astronomers to calculate the average density of an asteroid. It is about half the density of iron. The low density of Cleopatra, which is thought to be composed of a high iron material, suggests that the body could be highly porous and have a structure known as a “pile of rubble.”
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According to Brož, this would mean that Cleopatra was probably formed after a large collision by regrouping the fragments.
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The incoherent structure and way the asteroid rotates also suggests how its moons may have formed. Cleopatra rotates at almost a critical speed, the speed at which the body would begin to disintegrate. The impacts of small bodies can thus throw boulders out of the surface.
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Thus, Cleopatra may have really “breathed life” into her moons.
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