Dust Discs Spotted Around Stars at Earth-like Distances

Discs of rocky and dusty material have been spotted orbitingaround two young stars at distances similar to the distance between the Earthand the sun.

Observing these discs is part of the quest to find Earth-likeplanets orbiting other stars. The discs could indicate collisions betweenasteroids or comets and planets in these systems, giving astronomers a viewinto the planet-forming conditions in other stellar systems.

Astronomers detected the dusty discs around the two starsusing the MIDI interferometer, an instrument that combines the infrared lightfrom the 8-m diameter telescopes of the EuropeanSouthern Observatory's Very Large Telescope in Chile, simulating a singletelescope with a mirror more than 100 meters in diameter.

The two stars are similar to our sun ? one is a littlecooler and one a little hotter.

Dusty details

The first, catalogued as HD 69830, is an orange star thoughtto be about 2 billion years old (compared with the Sun's age of 4.6 billionyears). HD 69830 lies in the direction of the southern constellation of Puppis,is around 41 light-years from the sun and is knownto have three planets with masses comparable to Neptune.

The second star, Eta Corvi (in the constellation of Corvusand 59 light-years from the Sun) is a yellow-white color, and is about 1.3billion years old.

Earlier observations hinted at discs of material around bothstars. Cold material was previously confirmed around Eta Corvi at about 14billion miles (22.5 billion km) from that star, a distance at which such a discwas easier to spot. The MIDI observations though have found discs much closerin to the two stars.

MIDI found the relatively small dusty disc around HD 69830sitting between 4.7 million and 224 million miles (7.5 million and 360 millionkm) from the star. If you were standing on the surface of one of its planets,this dust would be a spectacular sight, several thousand times brighter thanthe similar but much fainter zodiacal dustthat can be seen from Earth on a dark night.

One intriguing possibility for the source of the dust isthat the planets around HD 69830 are experiencing a high rate of impacts fromasteroids and comets smashing into their surfaces.

A similar disc is also found close in to Eta Corvi, lyingbetween 15 million and 280 million miles (24 million to 450 million km) fromits stellar host. For comparison the Earth is on average about 93 million miles(150 million km) away from the sun.

Why it matters

Dust disks have been found around other stars. But theseresults, announced this week at the Royal Astronomical Society's NationalAstronomy Meeting in Glasgow, Scotland, represent the first resolution of dustydiscs so close in to their parent stars.

The ages of the two stars and the locations of the dustydisks suggests that they may either originate from the debris of recentcollisions of massive objects or travel there from an outer, cooler disc likethe one around Eta Corvi.

"By probing regions of a similar scale to the Earth'sorbit we have the potential to observe the dusty results of massive collisionsin the final stages of rocky planet formation, and learn about the conditionsEarth-like planets in other planetary systems may experience," said RachelSmith of Keele University in Newcastle-under-Lyme, England, and one of theastronomers who observed the discs. "The opportunities for directlytesting our theories for how planets form and evolve have never beengreater."

The results of the study are also detailed in the journalAstronomy and Astrophysics.

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