Meet Kleopatra: the weird ‘dog-bone asteroid’ that fascinates astronomers

An artist's impression of the 'dog-bone asteroid' over Italy (Credits: ESO/M. Kornmesser/Marchis et al.)
An artist’s impression of the ‘dog-bone asteroid’ over Italy (Credits: ESO/M. Kornmesser/Marchis et al.)

A bizarre asteroid that looks like a giant dog bone has been captured by astronomers.

The space rock, named Kleopatra, orbits the Sun between Mars and Jupiter – and has two moons.

It is the most unusual object in the Solar System – and is spinning at astonishing speed.

The object has fascinated stargazers for 140 years – since it was first spotted in 1880.

Two lobes connected by a thick ‘neck’ led it to be dubbed the ‘dog-bone asteroid’.

Mostly metal, it’s 168 miles long and 58 miles wide – much bigger than previously believed.

The new images show Kleopatra in unprecedented detail – viewed at different angles as it rotates.

They were taken at different times between 2017 and 2019 by the Very Large Telescope (VLT) in Chile’s Atacama Desert.

Eleven images of the asteroid Kleopatra, viewed at different angles as it rotates through space
Eleven images of the asteroid Kleopatra, viewed at different angles as it rotates through space (Credits: EPA)

Lead author Dr Franck Marchis, of the SETI Institute in Mountain View, California, said: ‘Kleopatra is truly a unique body in our Solar System.

‘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.’

Kleopatra is 125 million miles from Earth at its closest. Its apparent size on the sky is equivalent to a golf ball about 25 miles away.

The observations identify its dimensions and mass more accurately than ever before – also shedding light on how its orbiting moons formed.

They were discovered in 2008 by the same group who named them AlexHelios and CleoSelene – after the Egyptian queen’s children.

Kleopatra is believed to be the remnant of an incredibly violent collision between two asteroids that did not completely shatter and disperse.

The international team created 3D models based on the various snapshots. One lobe is larger than the other.

A 3D image showing the Kleopatra asteroid over Chile (Credits: ESO/M. Kornmesser/Marchis et al.)
A 3D image showing the Kleopatra asteroid over Chile (Credits: ESO/M. Kornmesser/Marchis et al.)

A second study also showed Kleopatra’s density is only 3.4 grams per cubic centimetre – rather than an earlier estimation of 4.5 grams.

It is half that of iron – meaning its mass is about a third (35%) less than thought. Its moons are in different locations to those predicted.

Lead author Professor Miroslav Broz, of Charles University in Prague, said: ‘This had to be resolved.

‘Because if the moons’ orbits were wrong, everything was wrong, including the mass of Kleopatra.’

The new data and sophisticated modelling enabled the international team to precisely describe how Kleopatra’s gravity influences the complex movements of AlexHelios and CleoSelene.

The low density suggests Kleopatra has a porous structure and could be little more than a ‘pile of rubble’.

It adds to evidence it was likely formed when material reaccumulated following a giant impact.

The asteroid rotates at such speed any faster it would start to fall apart – and even small impacts may lift pebbles off its surface.

Dr Marchis and colleagues say those could subsequently have created AlexHelios and CleoSelene – meaning Kleopatra birthed its own moons.

The images and insights were possible thanks to one of the most advanced adaptive optics systems on ESO’s (European Space Observatory’s) VLT.

It helps correct for distortions caused by the Earth’s atmosphere which make objects appear blurred – a phenomenon behind ‘twinkling’ stars.

It enabled the SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) instrument to collect the sharpest pictures to date.

ESO’s upcoming ELT (Extremely Large Telescope) will be even more ideal for imaging distant asteroids such as Kleopatra.

Every year in mid-August the Perseid meteor shower has its peak. Meteors, colloquially known as ???shooting stars???, are caused by pieces of cosmic debris entering Earth???s atmosphere at high velocity, leaving a trail of glowing gases. Most of the particles that cause meteors are smaller than a grain of sand and usually disintegrate in the atmosphere, only rarely reaching the Earth???s surface as a meteorite. The Perseid shower takes place as the Earth moves through the stream of debris left behind by Comet Swift-Tuttle. In 2010 the peak was predicted to take place between 12???13 August 2010. Despite the Perseids being best visible in the northern hemisphere, due to the path of Comet Swift-Tuttle's orbit, the shower was also spotted from the exceptionally dark skies over ESO???s Paranal Observatory in Chile. In order not to miss any meteors in the display, ESO Photo Ambassador St??phane Guisard set up 3 cameras to take continuous time-lapse pictures on the platform of the Very Large Telescope during the nights of 12???13 and 13???14 August 2010. This handpicked photograph, from the night of 13???14 August, was one of Guisard???s 8000 individual exposures and shows one of the brightest meteors captured. The scene is lit by the reddened light of the setting Moon outside the left of the frame. Although the comet debris particles are travelling parallel to each other, the meteors appear to radiate from a spot on the sky in the constellation of Perseus (here seen very low on the horizon and partly covered by the VLT enclosures). This effect is due to perspective, as the parallel tracks seem to converge at a distance. The apparent origin in Perseus is what gives the Perseid meteor shower its name. Around the globe, many thousands of people were out observing the Perseids. Some of them took part in citizen science projects such as Meteorwatch and the annual campaign organised by the International Meteor Organization (IMO). According to the IMO measurements, the 2010 Per
The ESO’s so-called ‘Very Large Telescope’ (VLT) complex in Chile captured the new images of Kleopatra (Credits: ESO/S. Guisard)

Added Dr Marchis: ‘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.’

Kleopatra is one of several dozen asteroids whose colouring suggests they contain metal.

Its strong reflection of radar signals indicates it’s mainly metal – possibly a nickel-iron alloy.

These objects were once heated, melted and differentiated into structures containing a core, mantle and crust, much as the Earth was formed.

Unlike Earth, those asteroids cooled and solidified throughout, and many underwent massive collisions that exposed their metallic cores.

In some cases, those collisions launched fragments that eventually collided with Earth, becoming iron meteorites like the one that created Meteor Crater in Arizona.

The findings appear in two papers in the journal Astronomy & Astrophysics.

MORE : China proposes gigantic rocket strike to divert asteroid which could hit Earth

MORE : Nasa defence exercise shows even nuclear bombs wouldn’t stop a deadly asteroid impact

Tech Science Space and time