The infrared spectra of interplanetary dust collected in the stratosphere indicate that the particles are similar to the stuff of comets and protostellar clouds, according to an international research team that published its findings in the Sept. 10 issue of Science. The results of the study suggest that interplanetary dust is the purest and most primitive astrophysical material available for understanding the evolution of the solar system. The researchers analyzed thin sections of the 15-µm-diameter particles with a 10-µm infrared beam from the National Synchrotron Light Source at Brookhaven National Laboratory in Upton, N.Y. The spectra of subpicogram glassy silicate crystals in the dust grains revealed two varieties: those that match the magnesium-rich comets and pre-main sequence stars, and those that match the amorphous silicates found in molecular clouds and young stellar objects. The cometary dust is unique because chondritic meteorites and micrometeorites rarely display magnesium-silicate crystals. The particles that correspond to the spectra of prestellar molecular clouds, however, are far more significant; they are likely the remnants of the cloud from which our solar system emerged.