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New 3D model shows ‘dog bone’ asteroid is lighter than previously thought

The new findings suggest the Kleopatra asteroid may be little more than a “pile of rubble" that likely formed when material regathered following a giant impact.

(CN) — A team of astronomers have captured the most detailed images to date of the asteroid Kleopatra, which has allowed them to create a 3D model of its shape and determine that its mass and density are lower than previous estimates.

Kleopatra, first discovered in 1880, orbits the sun in the asteroid belt between Mars and Jupiter. Its peculiar dog bone shape has made it stand out since 2000, when radar observations revealed the New Jersey-sized asteroid has two lobes connected by a thick “neck.” Eight years later it was discovered to be orbited by two moons named after the Egyptian queen’s children, AlexHelios and CleoSelene.

Earlier research calculated the asteroid’s mass after first charting the orbits of the two small moons, but two new research papers published Thursday in the journal Astronomy & Astrophysics find that the moons were not where the older data predicted them to be. 

“This had to be resolved,” Miroslav Brož of Charles University in Prague, Czech Republic, said in a statement. “Because if the moons’ orbits were wrong, everything was wrong, including the mass of Kleopatra.”

To do that, Brož used data collected by Franck Marchis, an astronomer at the SETI Institute in Mountain View, California.

Marchis and his team, who first discovered Kleopatra’s moons in 2008, used the European Southern Observatory’s Very Large Telescope — located in the Atacama Desert in Chile — to take snapshots of the asteroid at different times between 2017 and 2019 as it rotated.

The ESO telescope’s adaptive optics help correct distortions caused by the Earth’s atmosphere, which causes objects to appear blurred — the same effect that causes stars to twinkle. 

With those images, researchers created a 3D model, finding that one of the lobes is larger than the other.

With that new information, Brož’s team was able to calculate how Kleopatra’s gravity influences the moons’ orbits. That allowed them to come up with a more accurate calculation of the asteroid’s mass, finding it to be 35% lower than previous estimates.

The new findings also allowed astronomers to more accurately calculate the density of the asteroid, which also turned out to be lower than previously thought.

The low density of Kleopatra, which is believed to have a metallic composition, suggests that it has a porous structure and may be little more than a “pile of rubble.” That indicates it likely formed when material regathered following a giant cosmic impact.

Additionally, because the asteroid rotates at near “critical” speed — the speed above which it would start to fall apart — even small-object impacts could lift pebbles off its surface. 

Marchis and his team believe that those pebbles could subsequently have formed AlexHelios and CleoSelene, meaning that Kleopatra may have indeed birthed its own moons.

“Kleopatra is truly a unique body in our solar system,” Marchis said in a statement. “Science makes a lot of progress thanks to the study of weird outliers. I think Kleopatra is one of those and understanding this complex, multiple asteroid system can help us learn more about our solar system.”

Understanding the solar system is important, he added, because it forces researchers to “revise our theories, build new models and more importantly drop our prejudice (asteroids are not flying rocks, they are geologically active worlds) making some scientists think outside the box.”  

“That’s what I like the most in this research which started with the discovery of the first moon around asteroids,” he said.

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