Six White Dwarfs with Circumstellar Silicates

Spitzer Space Telescope spectra reveal 10 μm silicate emission from circumstellar dust orbiting six externally polluted white dwarfs. Micron-size glasses with an olivine stoichiometry can account for the distinctively broad wings that extend to 12 μm these particles likely are produced by tidal disruption of asteroids. The absence of infrared polycyclic aromatic hydrocarbon features is consistent with a scenario where extrasolar rocky planets are assembled from carbon-poor solids.