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Last Updated: Wednesday, 20 April, 2005, 18:53 GMT 19:53 UK
Dusty debris may be asteroid belt
Concept view of asteroid belt viewed from alien world (Nasa/JPL/Spitzer)
The discovery informs our understanding of possible distant "Earths"
The Spitzer telescope has detected what looks to be an asteroid belt around a star some 41 light-years from Earth.

US astronomers say that if confirmed it would be the first such band of rocky material found around a star of similar age and size to our own Sun.

The alien girdle is quite close to its star, known as HD69830, and is much thicker than the asteroid belt seen between the orbits of Mars and Jupiter.

The scientists hope to use the Spitzer data to learn about planet formation.

"We're interested in asteroid belts because they may mark the construction sites that accompany the formation of rocky planets; the junkyards that remain after the formation of such planets; or simply mark places where for one reason or another material just couldn't assemble to form planets at all," explained Dr Charles Beichman, of the California Institute of Technology.

Beichman is the lead author of a paper on the Spitzer discovery that will appear in the Astrophysical Journal.

Dust clues

Spitzer has not seen large asteroids directly. What it has detected is the warm glow from dust grains in the suspected belt.

This dust is the fallout from rock collisions, which occur relatively frequently, about every 1,000 years.

The grains have been heated by the star to temperatures that range "from room temperature to that of a hot 450-degree oven". Spitzer's infrared systems are tuned to pick up just such a signature.

"Because this belt has more asteroids than ours, collisions are larger and more frequent, which is why Spitzer could detect the belt," said Dr George Rieke, from the University of Arizona, Tucson, and a co-author of the paper.

"Our present-day Solar System is a quieter place, with impacts of the scale that killed the dinosaurs occurring only every 100 million years or so."

HD69830, which lies in the northern constellation of Puppis, is probably just a couple of billion years younger than our Sun, and with a slightly lower power output.

There are two other known distant asteroid belts, but they circle even younger and more massive stars.

Constant bombardment

The Spitzer team will have to do some further observations to be absolutely sure it has actually seen an asteroid belt.

It is just possible that what has been detected is the dust trail of a giant comet, but the team says its current data makes this scenario unlikely.

Nasa's Spitzer infrared telescope

HD69830 is not known to have any planets in orbit around it, let alone small, rocky worlds like Earth. Current telescope technology is simply not good enough to see such detail.

But if there is an Earth there, it could be an uncomfortable place.

"The frequency of impacts from this massive asteroid belt would be much larger than we experience on the Earth and so extinctions would be extremely frequent and there is a valid question that could be asked about whether life could actually take hold and evolve on such a world," commented Dr Jonathan Lunine, from the University of Arizona, Tucson.

Plenty of Earths await discovery
05 Apr 05 |  Science/Nature
Spitzer sees far-off planet light
24 Mar 05 |  Science/Nature
Telescopes see 'distant planet'
04 Apr 05 |  Science/Nature
Mini-planet system seen in growth
08 Feb 05 |  Science/Nature
In pictures: Telescope pierces space dust
18 Dec 03 |  Photo Gallery
Nasa launches Universe probe
26 Aug 03 |  Science/Nature


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