An international team of scientists has obtained the sharpest and most detailed images of the asteroid Cleopatra, which looks like a dog’s bone. They were obtained with the VLT (Very Large Telescope) telescope. The discovery will allow scientists to determine how the asteroid formed. Polish astronomers from the Adam Mickiewicz University in Poznań took part in the research.
The European Southern Observatory (ESO) has announced the latest research from the VLT (Very Large Telescope) telescope operating in the Atacama Desert in Chile. Scientists from the team led by Franck Marchis, an astronomer from SETI Institute in Mountain View (USA) and Laboratoire d’Astrophysique de Marseille (France), decided to carefully study the asteroid (216) Cleopatra.
The object orbits the sun in the main asteroid belt between the orbits of Mars and Jupiter. However, it is unusual. Since the first radar observations around 20 years ago to estimate the shape, it has earned the nickname “dog bone asteroid” from its shape showing two lobes connected by a “neck”, similar to a dog’s bone. In 2008, Marchis and colleagues discovered that Cleopatra had two moons, named AlexHelios and CleoSelene, after the names of the children of the famous Egyptian Queen Cleopatra.
“Cleopatra is a truly unique body in our solar system,” said Franck Marchis. – Science is making significant progress through the study of abnormal values. I think Cleopatra is one such case, and understanding this complex, multiple asteroid system can help us learn more about the solar system, ‘he added.
The latest research of the object includes the analysis of images taken at different times in 2017-2019 with the SPHERE instrument on the VLT. One of the lobes was found to be larger than the other, and the asteroid’s length was estimated to be around 270 kilometers. It was also possible to better determine the orbits of the asteroid’s moons and determine the mass again (it was 35 percent lower than previous estimates). In turn, knowing the volume and mass, it is possible to determine the average density of the asteroid, which also turned out to be lower than previously believed.
The density is approximately half that of iron. Astronomers speculate that the asteroid Cleopatra has a metallic composition, so the low density suggests a porous structure and the object could simply be a “pile of debris”. It may have arisen when material from the big impact had accumulated again.
The debris structure and the way the asteroid rotates also allow us to hypothesize about the formation of moons. The asteroid rotates near its critical speed, that is, the speed at which it would start to decay. Thus, even small blows could knock stones off its surface. These stones could then form the moons of AlexHelios and CleoSelene, meaning Cleopatra really “gave birth” to her satellites.
Cleopatra asteroid. Participation of Polish scientists
Polish astronomers from the University of Warsaw participated in the research. Adam Mickiewicz in Poznań. Among them was Dr. Edyta Podlewska-Gaca, who collected photometric observations made on small telescopes (light curves), which, together with images from the SPHERE instrument mounted on the VLT telescope, are used to model the shapes of asteroids, determine physical parameters and determine their dynamic history.
Cleopatra asteroid. Unique method of determining the shape based on algorithms
Poznań astronomers specialize in the study of asteroids. They developed and use a unique method for determining the shape of asteroids based on genetic algorithms.
– This method works very well in modeling non-convex objects, thanks to which it allows to reproduce pits or large craters on the surface of asteroids. Thanks to this method, it is possible to verify and refine the models obtained using other techniques – points out Dr. Podlewska-Gaca. As he explains, the shapes of asteroids are most often determined from the curves of brightness changes obtained for different positions of the object’s rotation axis relative to the observer. Then you can observe the asteroid from different angles, which gives a slightly different shape of the glow curve. It is these changes that provide valuable information about the shape of objects. – The asteroid models determined in this way can be verified by observing star covers by asteroids or by high-resolution imaging using adaptive optics, as we did with the Cleopatra asteroid, she added.
The results were published in two articles in the journal Astronomy & Astrophysics.
Main photo source: European Southern Observatory