Cometary dust in the planetary belts of β Pictoris

The discovery of more than 600 exo-planets in the past two decades has shown an amazing diversity in the properties of planetary systems. The origin of this diversity and the way the Solar Systemfits inmust be understood by studying young systems in which planet formation is ongoing, and by comparing the properties of these young systems with the historic records of the formation of the Solar System as recorded in e.g. asteroids and comets. Strong evidence that gas-phase condensation produces Mg2SiO4, comes from observations of crystalline olivine grains in evolved
cool red giants. In another study we have detected the 69 μm crystalline olivine band in several red giants and the wavelength and band shape of the resonance are in agreement with pure Mg2SiO4. In contrast, Solar Systemcomets such as Wild 2 and chondritic meteorites show a small but significant fraction of Fe in the crystalline olivine of "1 per cent. β Pictoris is a young (12 Myr) main-sequence star surrounded by at least one planet at a distance of "10 AU, and a dusty debris disk created by catastrophic collisions of planetesimals. We have detected the 69 μm band in a HERSCHEL- PACS Range Scan of β Pictoris. Modeling this band gives an Fe/Mg ratio of 0.01 and constrains the location of the crystalline olivine to 8-16 AU. The crystalline olivine grains are probably produced by collisions
between planetesimals in the known belts at 6 and 16 AU. The composition of the crystalline olivine is strikingly similar to that of Solar System bodies like comets, IDPs and meteorites. But an Fe/Mg ratio of 0.01 is not compatible with crystalline olivine grains produced through gas phase condensation, meaning that the crystalline olivine in β Pictoris must come from another source, similar to the one in our Solar System.