Asteroid found in exile in outer Solar System

An asteroid has been found in the Kuiper Belt. The object most likely originated from the asteroid belt, but was thrown out early on in the Solar System's history.

The asteroid is a relic of the gravitational upheaval that occured during the early eras of the Solar System. Credit: ESO/M. Kornmesser
Published: May 10, 2018 at 12:00 pm
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An asteroid found in exile in the outer reaches of the Solar System has had its composition confirmed by ESO’s Very Large Telescope (VLT).


The study of asteroid 2004 EW95 revealed that it was carbon-rich, meaning it most likely originated in the asteroid belt between Mars and Jupiter but was flung out into the Kuiper Belt – the region of icy objects beyond Neptune – backing theories that the asteroid belt was once much larger than it is today.

The research team’s attention was first drawn to the rocky body when it was routinely observed with the Hubble Space Telescope, which found that the pattern of reflected light – known as its reflectance spectrum – from the object suggested it was more than a simple Kuiper Belt object.

“The reflectance spectrum of 2004 EW95 was clearly distinct from the other observed outer Solar System objects,” says Tom Seccull of Queen’s University Belfast who led the study.

“It looked enough of a weirdo for us to take a closer look.”

The team took more detailed measurements using the VLT, and found signs of iron oxides and sheet silicates called phyllosilicates which suggested that the rock formed in the inner Solar System.

“Given 2004 EW95’s present-day abode in the icy outer reaches of the Solar System, this implies that it has been flung out into its present orbit by migratory planet in the early days of the Solar System,” says Seccull.

Astronomers theorise that such a planetary shuffle may have happened early in the Solar System’s history, creating a huge gravitational imbalance and reducing the number of asteroids in the asteroid belt to a fraction of its original number.

If such an event did occur, then several of the asteroids would not have been captured in the Kuiper Belt.

“While there have been previous reports of other ‘atypical’ Kupier Belt Object spectra, none were confirmed to this level of quality,” says Oliver Hainaut, an ESO astronomer.


“The discovery of a carbonaceous asteroid in the Kuiper Belt is a key verification of one of the fundamental predictions of dynamical models of the early Solar System.”


Ezzy Pearson is the News Editor of BBC Sky at Night Magazine. Her first book about the history of robotic planetary landers is out now from The History Press.


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