Astronomers discover an asteroid is actually two — and that it’s also a comet – Technology & Science

When is an asteroid not just an asteroid? When it’s a comet.

Astronomers using the Hubble Space Telescope have found that an asteroid discovered in 2006 is actually two — and that it sprouts a tail just like a comet.

While comets originate from beyond Neptune in a region called the Kuiper Belt, asteroids orbit the sun in two locations, the main one being the asteroid belt between the orbits of Mars and Jupiter.

However, in 2011, astronomers discovered that asteroid 300163 (2006 VW139) was displaying some cometary activity and gave it the cometary designation of 288P. 

Then, in September 2016, just before it made its closest approach to the sun, astronomers from the Max Planck Institute for Solar System Research imaged the asteroid/comet and got a pleasant surprise. Instead of seeing a single asteroid, they found two.

The pair are almost the same mass and size and orbit one another about 100 kilometres apart. This is the first time two asteroids that orbit one another — collectively called a binary asteroid — have also been classified as a comet.

An illustration depicts where most asteroids are found in our solar system: the asteroid belt between Mars and Jupiter, and the Trojans, two groups of asteroids moving ahead of and following Jupiter in its orbit around the Sun. (ESA/Hubble, M. Kornmesser)

While there had been some suspicion that it could be two asteroids, astronomers were thrilled to be able to confirm it.

‘It’s something we haven’t seen yet, and we don’t know why’
– Jessica Agarwal, Max Planck Institute for Solar System Research

“It was very nice to see that, indeed, we had the right suspicion,” Jessica Agarwal, lead author of the study published in Nature, and astronomer at the Planck Insttitute, told CBC News.

There are few asteroids considered to also be comets. That’s because comets are made primarily of ice and dust, sprouting tails as they orbit the sun. This occurs due to a process called sublimation, when the ice skips the water stage and goes straight to a gas, producing the tail we see.

Asteroids, on the other hand, are typically rocky, with little water ice. It’s believed that millions of these mostly irregularly shaped rocky worlds exist in two regions orbiting the sun. 

So to have a binary system with cometary activity is unusual.

“It’s something we haven’t seen yet, and we don’t know why,” Agarwal said.

Answering questions

While asteroids are believed to be as old as the solar…

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