Astronomers have captured the best images yet of a strange ‘dog bone’ asteroid called Cleopatra. The images revealed that the rock is larger than previously thought.
The asteroid, made of mostly metal, orbits the sun between Mars and Jupiter, and is 168 miles long and 58 miles wide, making it twice the size of Hadrian’s Wall. Previous estimates put it at 134 miles long and 58 miles wide.
Resembling a giant dog bone, the exotic space rock has fascinated stargazers since it was first discovered in 1880 by Austrian astronomer Johann Balesa.
The asteroid consists of two lobes connected by a thick “neck”. The new images, taken by the Very Large European Southern Observatory telescope in Chile, reveal a strange asteroid from different angles as it rotates.
They were captured at different times between 2017 and 2019, when an international team led by the Search for Extraterrestrial Intelligence (SETI) Institute in Mountain View, California, processed the images.
The asteroid “Cleopatra” is located 125 million miles from Earth at its closest point, which means that its apparent size in the sky is equivalent to watching a golf ball from about 25 miles away.
Lead author Dr. Frank Marches said Cleopatra is truly a unique object in our solar system, and the new observations provide more details about its composition.
Science is making a lot of progress thanks to the study of exotic outliers. “I think Cleopatra is one of those, and understanding this complex, multi-asteroid system can help us learn more about our solar system,” said Dr. Marches.
In September 2008, Marchis and his collaborators announced that the unusual asteroid had two moons, later named Alexhelios and Cleoselene, after Cleopatra’s children Alexander Helios and Cleopatra Selene II.
The new Very Large Observatory (VLT) observations determine the dimensions and mass of the asteroid more precisely than ever before, and also shed light on how its orbiting moons formed.
The asteroid “Cleopatra” is believed to be the remnant of an incredibly violent collision between two asteroids that did not completely break apart.
The international team created 3D models based on various snapshots taken by the Very Large Observatory (VLT), and found that one lobe is larger than the other.
A second study also showed that Cleopatra had a density of 3.4 g per cubic centimeter, instead of an earlier estimate of 4.5 g.
This density is half the density of iron, which means that the size of the strange asteroid is one-third less than previously thought, and the moons are in a different location.
Prof Miroslav Pros, from Charles University in Prague, said finding the moons’ location was wrong and had to be solved, “because if the moons’ orbits were wrong, then everything was wrong, including Cleopatra’s mass”.
New data and sophisticated modeling enabled the international team to accurately describe how Cleopatra’s gravity affects the complex movements of AlexHelios and CleoSelene.
The low density suggests Cleopatra has a porous structure and could be little more than a ‘pile of rubble’, adding to evidence that the asteroid likely formed when material accumulated together after a massive impact.
The structure of Cleopatra’s “mound of rubble” and the way the asteroid orbits give indications of how its moons formed.
The asteroid rotates almost at a very fast speed, the speed at which the asteroid begins to collapse and any small impact from another space rock can fly pebbles from its surface into space.
Marchis and his team believe those pebbles could have formed later on AlexHelios and CleoSelene, which means Cleopatra did indeed give birth to its own moons.
The European Southern Observatory’s Very Large Telescope (ELT) would be more ideal for photographing distant asteroids such as Cleopatra.
Dr Marchis added: “I can’t wait to point the very large telescope at Cleopatra, to see if there are more moons and to improve its orbits to detect small changes.”
Cleopatra is one of dozens of asteroids whose coloration indicates that they contain metal due to their strong reflection of radar signals.