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UCSD Astronomer Ponders Disappearing Space Dust

Aired 7/9/12 on KPBS News.

The disappearance of a field of space dust around a distant star has rattled theories of how planets are formed.

There's a star, about 456 light years from earth, that has won the attention of Carl Melis, a post-doctoral researcher at UC San Diego. It attracted the astronomer's eye because it's surrounded by a disc of dust and rocks. And it became even more interesting when its dust field disappeared.

A field of dust and rocks as shown in artwork by Lynette Cook.
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Above: A field of dust and rocks as shown in artwork by Lynette Cook.

Scientists believe space dust is the stuff that planets are made of. As dust and rocks swirl around a star, they grow by what's called "collisional accumulation."

"That's basically where you take some rocks and you smash them together," said Melis. "Some of the parts of the rock stick together, and the rock begins to grow."

Pretty soon you've got another terrestrial planet.

But something strange happened as Melis was observing his star, which is about the size of our sun. The bright disk of dust disappeared over a period of only two years. That's a blink of an eye in the life of a star.

This had never been seen before. Melis theorized the event could be caused one of a few ways. Maybe the rocks collided in a way that caused them to not accumulate, but to be so pulverized and light they just blew away into space. Astro-boys call that process a collisional cascade.

Melis said the dusk then may have been blown away by the radiative force of the starlight.

"It can actually be greater than the gravitational force of the star, and the dust grains will just float away from the stellar system," he said.

So what does this tell us about creating planets?

This doesn't mean no planets will form around Melis's sun. But it could mean the cyclical process of dust fields forming, and becoming plants, happens faster than we once thought.

The research is published in the journal Nature.

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