See Weird Dog Bone-shaped Asteroid, Half the Length of Grand Canyon With Two Moons
Using the European Southern Observatory's (ESO) Very Large Telescope (VLT), astronomers have made detailed observations of a most extraordinary asteroid and discovered that it is an impressive 167 miles long. The detailed observations of the asteroid Kleopatra also allowed the team to learn more about its shape, which resembles a dog bone.
Beyond uncovering details about its curious shape, the researchers' work could also shed light on how the asteroid—which orbits the Sun by passing between Mars and Jupiter in the Main Asteroid Belt—and its two moons evolved. The paper was published on Thursday in the journal Astronomy & Astrophysics.
"Kleopatra is truly a unique body in our Solar System," co-author Franck Marchis, an astronomer at the SETI Institute in Mountain View, U.S. and at the Laboratoire d'Astrophysique de Marseille, France, told Newsweek. "Its weird bone shape, the presence of those two moons, the low density for a supposedly metallic asteroid, and finally the fact that the moons could be an infant of the main asteroid formed by the ejection of pebbles and boulders make the Kleopatra triple system a very weird main-belt asteroid that deserves our attention."
Marchis has a history with Kleopatra, which exists around 124 million miles from Earth. In 2008, he was one of the researchers who discovered that it possesses its own moons dubbed AlexHelios and CleoSelene, after the Egyptian queen's children.
To discover more about the asteroid, Marchis and the team collected images taken over two years, 2017 and 2019, with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on ESO's VLT, located at the Paranal Observatory in the Atacama Desert of northern Chile.
Because the images were taken as the asteroid rotated, the astronomers were able to view it from all angles, building the most accurate 3D model of Kleopatra ever created.
From this model, they were better able to determine Kleopatra's shape, finding that one lobe of the asteroid is larger than the other and determining its total length is 169 miles long—over half the length of the Grand Canyon.
Astronomers were not done with the study of Kleopatara and its moon here though. In a separate study, also published in Astronomy & Astrophysics on Thursday, a team led by Miroslav Brož of Charles University in Prague, Czech Republic, used SPHERE observations to track the orbit of the asteroid's moons.
Brož told Newsweek: "I was informed by my Czech and French coworkers, Josef Hanus and Pierre Vernazza, that new astrometric measurements of the moons obtained by the VLT/SPHERE seem to be 'suspicious.' When this happens, it is an opportunity to discover something.
"This had to be resolved. Because if the moons' orbits were wrong, everything was wrong, including the mass of Kleopatra."
The researcher added: "At about the same time, I had prepared a sophisticated program to compute orbits around very irregular bodies."
The new observations and the 3D modeling program allowed Brož and his team to better calculate how the gravity of Kleopatara influences AlexHelios and CleoSelene. They then tracked back from these orbits to find the main asteroid's mass, which is 35 percent less than previously estimated.
From here the astronomers could also work out the density of Kleopatra, finding the asteroid is less than half as dense as iron—also lower than previously believed.
This means that Kleopatra is likely a loose rubble pile that formed after some form of massive collision when material began to collect back together. The rubble-pile nature of the asteroid also gives a hint as to how its two moons formed.
The astronomers believe that as Kleopatara rotates at near-critical speed, the speed at which it would fly apart, even small impacts from other bodies in the Main Asteroid Belt would knock pebbles loose.
Marchis and his team believe that these pebbles came together and formed the two moons AlexHelios and CleoSelene. Learning more about the asteroid might have to wait a while.
"Our ultimate goal is to understand all big asteroids in the main belt, including their volume, mass, density, porosity, shape, as well as structure. We are not there yet," Brož said. "Generally, we think that about half of big asteroids are primordial, they have been accreted approximately 4.567 billion years ago. Another half were hit, colliding with another asteroid later on.
"Kleopatra is difficult to explain. Its extreme shape indicates an oblique collision, which resulted in a fast-rotating elongated body."
Viewing it now is like observing a golf ball from 25 miles away, a challenge for even the VLT and SPHERE. Fortunately, a more powerful telescope is currently under construction in the Atacama Desert, the Extremely Large Telescope (ELT).
And Marchis is relishing the chance to further investigate Kleopatra. The astronomer believes that the weird asteroid may hide more surprises still.
"The ELT which will provide an image resolution three to four times better than the VLT will definitely be the best tool to shine more light on the formation and evolution of this mysterious triple asteroid system," Marchis said.
"Eventually one day we will visit Kleopatra with a robotic space mission, and I can bet it will be a spectacular world to image, a shiny dog-bone asteroid surrounded by tiny moons."
