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

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

Astronomers detected the dusty discs around the two stars using the MIDI interferometer, an instrument that combines the infrared light from the 8-m diameter telescopes of the European Southern Observatory's Very Large Telescope in Chile, simulating a single telescope with a mirror more than 100 meters in diameter.

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

Dusty details

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

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

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

MIDI found the relatively small dusty disc around HD 69830 sitting between 4.7 million and 224 million miles (7.5 million and 360 million km) 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 than the similar but much fainter zodiacal dust that can be seen from Earth on a dark night.

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

A similar disc is also found close in to Eta Corvi, lying between 15 million and 280 million miles (24 million to 450 million km) from its 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 these results, announced this week at the Royal Astronomical Society's National Astronomy Meeting in Glasgow, Scotland, represent the first resolution of dusty discs so close in to their parent stars.

The ages of the two stars and the locations of the dusty disks suggests that they may either originate from the debris of recent collisions of massive objects or travel there from an outer, cooler disc like the one around Eta Corvi.

"By probing regions of a similar scale to the Earth's orbit we have the potential to observe the dusty results of massive collisions in the final stages of rocky planet formation, and learn about the conditions Earth-like planets in other planetary systems may experience," said Rachel Smith of Keele University in Newcastle-under-Lyme, England, and one of the astronomers who observed the discs. "The opportunities for directly testing our theories for how planets form and evolve have never been greater."

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