These 11 images show the asteroid Kleopatra from different angles, as it rotates. These images were taken with the SpectroPolarimetric High Contrast Exoplanet REsearch instrument (SPHERE), on ESOs VLT. They were taken at various times in 2017 and 2019. Kleopatra orbits Jupiter and Mars in the Asteroid Belt. Since radar observations 20 years ago showed it had two lobes linked by a thick neck, astronomers have called it a "dog-bone asteroid". Credit: ESO/Vernazza et al./MISTRAL algorithm. (ONERA/CNRS).
A team of astronomers has obtained the most precise and sharpest images of Kleopatra using the European Southern Observatory's Very Large Telescope. These observations allowed the team of astronomers to determine the 3D shape, mass, and structure of the asteroid Kleopatra, which is similar to a dog bone. The team's research has provided clues to the formation of this asteroid, and the moons it orbits.
Franck Marchis (an astronomer at SETI Institute, Mountain View, U.S.A., and at Laboratoire d'Astrophysique de Marseille in France) led a study of the asteroid, which has moons and a strange shape. It was published today in Astronomy & Astrophysics. The study of strange outliers is a key to science's progress. Kleopatra, I believe, is one of these outliers. Understanding this complex, multiple-asteroid system can help us understand more about the Solar System.
Kleopatra orbits Jupiter and Mars in the Asteroid Belt. Since radar observations 20 years ago showed it had two lobes linked by a thick neck, astronomers have called it "dog-bone" asteroid. Marchis and his coworkers discovered that Kleopatra orbits two moons. They were named AlexHelios (after the Egyptian queen) and CleoSelene (after the Egyptian queen's children).
Marchis and his team took snapshots of Kleopatra between 2017 and 2019, using the SpectroPolarimetric High Contrast Exoplanet REsearch instrument (SPHERE). They were able to see the asteroid from many angles and create 3D models of the shape. They determined that the asteroid had a dog-bone shape, was large in volume, and the length was approximately 270 km, or half of the length of The English Channel.
The second study was published in Astronomy and Astrophysics. It was led by Miroslav Bro, a Czech University professor, who reported on how the SPHERE observations were used to determine the orbits of Kleopatra’s moons. The orbits had been estimated in previous studies, but new observations using ESO's VLT revealed that they were not as predicted.
Bro. says, "This had to get resolved." Bro. says, "Because if all the moons' orbits were incorrect, then everything was wrong, even the mass of Kleopatra." The team was able to accurately describe how Kleopatra’s gravity affects the moons' movements, and to calculate the complex orbits for AlexHelios (and CleoSelene) thanks to sophisticated modeling and new observations. They were able to calculate the mass of the asteroid, which was 35% lower than previously estimated.
Astronomers combined the new volume and mass estimates to create a new value of the density of the Asteroid. This was less than half of what had been thought. Kleopatra's low density, which is thought to be metallic, indicates that it may have a porous structure. It could also be a "pile" of rubble. It is likely that it was formed from material that was reaccumulated after a huge impact.
The structure of Kleopatra's rubble piles and its rotation give clues to the formation of its moons. The asteroid rotates at almost a critical speed. This is the speed at which it would begin to break apart. Even small impacts can lift pebbles from its surface. Marchis and his team believe those pebbles could have formed AlexHelios or CleoSelene. This means that Kleopatra may have truly created its own moons.
One of the most advanced adaptive optics systems on ESO's VLT in Chile, located in the Atacama Desert, made it possible to create new Kleopatra images and provide insights. Adaptive optics corrects distortions in the Earth's atmosphere that cause objects to appear blurred. This is similar to how stars seen from Earth twinkle. SPHERE was able, thanks to these corrections to see Kleopatralocated 200,000,000 kilometers from Earth at its nearesteven though its apparent size is the same as a golf ball approximately 40 kilometers away.
ESO's Extremely Large Telescope, (ELT) will allow for the imaging of distant asteroids like Kleopatra with its advanced adaptive optics system. Marchis adds, "I cannot wait to point ELT at Kleopatra to see if they have more moons and refine their orbits for small changes."
Continue reading New insights into the origin of triple asteroid systems (87) Sylvia
Further information: (216). Kleopatra is a low-density critically rotating M type asteroid. Astronomy & Astrophysics (2021). (216) Kleopatra is a low-density critically rotating M type asteroid. arxiv.org/abs/2108.07207 An advanced multipole model for (216) Kleopatra triple system, Astronomy & Astrophysics (2021). arxiv.org/abs/2105.09134v1 Journal information: Astronomy & Astrophysics