Seeing into the heart of planetary systems

The astronomers used data from 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 to simulate the performance of a single telescope with a mirror more than 100 metres across.

Two of the stars observed with MIDI are similar to our Sun -- one is a little cooler and one a little hotter. The first, catalogued as HD69830, is an orange star with spectral type K0V and is thought to be about 2 billion years old (compared with the Sun's age of 4.5 billion years). It 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 spectral class F2V, equivalent to a yellow-white colour, and is about 1.3 billion years old. Earlier observations hinted at discs of material around both stars. Cold material was confirmed around eta Corvi as it lies 22.5 billion km from that star and so was easier to spot.

With MIDI the region of the relatively small dusty disc around HD69830 is clearly seen and lies between 7.5 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 the Earth on a dark night.

One intriguing possibility for the source of the dust is that the planets around HD69830 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 24 to 450 million km from its stellar host. For comparison the Earth is on average about 150 million km away from the Sun.

These results represent the first resolution of dusty discs so close in to their parent stars, observations made possible using an interferometer like MIDI. 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.

Dr Smith sees this work as part of the overall quest to find Earth-like planets around other stars. "With MIDI we have access to a truly giant telescope that can see the Universe in unprecedented detail. 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. The opportunities for directly testing our theories for how planets form and evolve have never been greater."