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Trillions of wrecked comets formed star's icy halo

Posted: April 13, 2012

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Using images from Europe's Herschel infrared space telescope, astronomers have obtained fresh insights into a forming solar system around the nearby star Fomalhaut, which features a ring of fine icy dust grains born out of the annihilation of thousands of comets each day.

This image from ESA's Herschel space observatory shows Fomalhaut and its icy debris ring. Credit: ESA
Herschel data allowed scientists to tweak their understanding of the youthful star, which a few hundred million years old and twice as massive as the sun, according to the European Space Agency.

"These beautiful Herschel images have provided the crucial information needed to model the nature of the dust belt around Fomalhaut," said Goran Pilbratt, ESA's Herschel project scientist.

Researchers discovered Fomalhaut's dust ring in the 1980s, but Herschel's data provide constraints on the temperature and size of the dust particles.

The dust grains are only a few millionths of a meter across, and their temperatures are between minus 284 degrees and minus 382 degrees Fahrenheit, scientists announced.

Artist's concept of the Herschel space observatory. Credit: ESA
The Fomalhaut research team, led by Bram Acke of the University of Leuven in Belgium, concluded the dust grains probably have a fluffy consistency. But bright starlight from Fomalhaut, which is 25 light years from the sun, should expel the low-density particles from the belt, leaving astronomers to deduce the dust must be continously replenished by pinball-like collisions of comets in the ring.

"To sustain the belt, the rate of collisions must be impressive: each day, the equivalent of either two 10 km-sized [6.2-mile] comets or 2,000 1 km-sized [.62-mile] comets must be completely crushed into small fluffy, dust particles," a statement released by NASA's Jet Propulsion Laboratory said.

"I was really surprised," Acke said. "To me this was an extremely large number."

NASA contributes to the European-led Herschel mission.

Scientists estimate there are between 260 billion and 8.3 trillion comets in the Fomalhaut belt. Our solar system's Oort cloud, a vast cloud of objects lying up to 100,000 times further from the sun than Earth, is believed to harbor a similar number of icy bodies.

Astronomers believe at least one planet orbits Fomalhaut between the star and the debris ring.