Low-temperature crystallization of silicate dust in circumstellar disks

Silicate dust in the interstellar medium is observed to be amorphous(1), ye t silicate dust in comets(2,3) and interplanetary dust particles(4) is some times partially crystalline. The dust in young stars(5,6) also appears to b e partially crystalline. These clouds to a planetary system, it must underg o some processing, Here we report observations of highly crystalline silica te dust in the disks surrounding binary red-giant stars. The dust was creat ed in amorphous form in the outer atmospheres of the red giants, and theref ore must be processed in the disks to become crystalline. The temperatures in these disks are too low for the grains to anneal; therefore, some low-te mperature process must be responsible. As the physical properties of the di sks around young stars and red giants are similar, our results suggest that low-temperature crystallization of silicate grains also can occur in proto planetary systems.