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Very Large Telescope captures best images yet of 'dog-bone' asteroid

Researchers captured 11 images of Kleopatra, a dog bone asteroid, using ESO's Very Large Telescope, providing new clues to how the asteroid and its moons formed. Photo by ESO/Vernazza, Marchis et al./MISTRAL algorithm
Researchers captured 11 images of Kleopatra, a "dog bone asteroid," using ESO's Very Large Telescope, providing new clues to how the asteroid and its moons formed. Photo by ESO/Vernazza, Marchis et al./MISTRAL algorithm

Sept. 9 (UPI) -- The European Southern Observatory's Very Large Telescope has provided astronomers their best view yet of Kleopatra, the "dog-bone" asteroid.

Using the high-resolution images captured by VLT, astronomers were able to precisely constrain the asteroid's shape and mass.

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The latest research -- detailed in a pair of papers, published Thursday in the journal Astronomy & Astrophysics -- may offer clues to the origin and evolution of Kleopatra and its two moons.

"Kleopatra is truly a unique body in our solar system," Franck Marchis, who led the investigation, said in a press release.

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"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," said Marchis, senior planetary astronomer at the SETI Institute in Mountain View, Calif.

Kleopatra's bone-like shape, two lobes connected by a thick neck, was first revealed by radar observations captured 20 years ago.

In 2008, Marchis and his research partners spotted Kleopatra's two moons. They named the pair AlexHelios and CleoSelene, after two of the Egyptian queen's three children.

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Researchers characterize Kleopatra's dimensions using images captured by VLT's SPHERE instrument between 2017 and 2019. Because Kleopatra is rotating, astronomers were able to capture images of the asteroid from a variety of angles.

The high-resolution images allowed scientists to construct an accurate 3D model of the asteroid, revealing its contours and volume. The research also confirmed one of Kleopatra's lobes to be larger than the other.

In addition to constraining the size and shape of Kleopatra, the SPHERE data also showed earlier estimates of the orbits of the asteroid's two moons to be flawed.

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"This had to be resolved," said Miroslav Bro┼ż, a researcher at Charles University in Prague, Czech Republic. "Because if the moons' orbits were wrong, everything was wrong, including the mass of Kleopatra."

Scientists used the new observations and model to estimate the influence of Kleopatra's gravity on the lunar orbits.

The calculations, in turn, allowed researchers to determine the asteroid's mass, revealing it to be 35% less than earlier approximations.

Kleopatra is thought to be composed of various metals, but its low density suggests it is highly porous and likely a conglomerate of rocks and rubble.

Because the rubble pile is rotating at such a high speed -- almost fast enough to cause the whole structure to come apart -- scientists suspect even minor impacts would be enough to jar material loose, which is likely how Kleopatra got its two moons.

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As revealing as VLT's images proved, astronomers are anxious to captured even higher-definition images using the Extremely Large Telescope, which is expected to capture "first light" in 2026.

"I can't wait to point the ELT at Kleopatra, to see if there are more moons and refine their orbits to detect small changes," said Marchis.

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