Birth of an Earthlike Planet Spied By Spitzer

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"We could actually tell what kind of dust is there" in the HD 113766 system, Lisse said. "In our case, it's rock and metal."

For example, the dust is rich in iron sulfides, a group of metals that includes the mineral pyrite, or fool's gold.

Lisse's team also noted what was not present in the dust: water ice and complex but fragile molecules known as hydrocarbons.

Thanks to the Deep Impact mission that analyzed the composition of Comet Tempel 1, the scientists knew that such materials would be expected if the dust was giving birth to comets.

(Read "Frozen Water Discovered on 'Deep Impact' Comet" [February 2, 2006].)

And studies of meteorites that have made their way to Earth suggest that dust coming off of large asteroids should not have as much metal.

This means that the astronomers are seeing HD 113766 just as the predecessor of a rocky planet, known as a planetesimal, is forming.

What's more, a cooler disk farther out from the star appears to contain icy dust, a possible source of water for the newborn planet.

For now, the proto-planet is probably zooming around inside the dust disk, Lisse said. And we may be able to catch signs of the system as its planet grows up.

HD 113776 has been observed a few times, "and we know [the amount of dust] hasn't died down too much over 20 years," Lisse said.

"If it's at the end [of forming planets], there would be a lot of bumping and scraping, but we might actually see it dying down" in the near future.

"Or if it's young, it could flare up," showing occasional signs of more collisions between rocks, which would stir up more dust.

"Stay tuned," Lisse added. "I expect lots more fireworks as the planet in HD113766 grows."

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