In a ring of dust

Oct 5, 2007 09:51 GMT  ·  By
Astronomers say a warm dust belt around the star HD 113766 (seen in this artist's depiction) is in the right spot with the right ingredients to form an Earth-like planet complete with liquid water.
   Astronomers say a warm dust belt around the star HD 113766 (seen in this artist's depiction) is in the right spot with the right ingredients to form an Earth-like planet complete with liquid water.

How did the Earth form? Astronomers have detected a "cooking" process for an Earth-like planet. The huge ring of hot dust surrounding a sun-size star 424 light-years away could be shaped into an Earth-like planet in a time period of maximum 100 million years.

The team investigating the infrared light coming from the star HD 113766 found a belt of dust and probably rock, the key raw materials necessary to create a planet, in the star's mildest zone, where water can still remain liquid. The dust composition also reveals it as just right for making a rocky planet, not a gaseous one.

"It's sitting damn, bang-smack in the middle of the habitable zone. That's really cool, because astronomers have never conclusively sighted a rocky planet forming in this "Goldilocks" zone," said lead author astrophysicist Carey Lisse of Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Md.

Planets emerge from the disk of material left around when a star comes to life. Analysis on comets shows that young solar systems abound in ice crystals and gases that gather into gas giants like Saturn and Jupiter, while rocky planets form after the gas was consumed.

"In particular, the Deep Impact mission blasted a crater in the comet Tempel 1 so astronomers could study the makeup of the debris, providing a "Rosetta stone" for interpreting the composition of material around stars," said Lisse.

Lisse's team used knowledge achieved from Deep Impact mission to investigate HD 113766, a young star (16 million years old) larger than the sun. Previous infrared camera observations made by the Spitzer Space Telescope revealed a swath of dust, with particles varying in size from 0.1 to 20 microns added up to a large asteroid and their temperature showed they were located at around 1.8 Earth-sun distances from their star.

The infrared data also showed the presence of rock and iron molecules, but no gas or other chemicals typical for comets. The rock and iron patterns did not resemble that from older asteroids or mature planets, thus the system recently entered the stage of rocky planet formation.

"We're seeing the building blocks of the earth. Such dust belts typically contain a spectrum of rocks of different sizes, and the distribution of dust strongly suggests at least one Mars mass worth of rocks 10 meters (30 feet) wide or smaller and up to several Earth masses of material if larger rocks are present, which is very plausible but more speculative." said Lisse.

"A planet would likely take 10 million to 100 million years to form from the ring. The only thing that might interrupt the process is if a gaseous planet had already formed and crossed the belt's path, sweeping up the rocky chunks before they could clump together," he added.