Particles with a wide range of masses (10−2–10−18 g) and velocities occurring in interplanetary, circumstellar, and interstellar space. They are typically porous with low densities and a ‘cluster of grapes’ morphology, but many are compact with densities of about 2000 kg/m3. Most particles collected from the stratosphere are comprised of layer lattice silicates, olivine, or pyroxene. In the terrestrial neighbourhood, they are mostly derived from comets and asteroids.