Small particles of solid matter found in space: in the Solar System (interplanetary dust and cometary dust), around stars (circumstellar dust), and between the stars (interstellar dust). The individual particles are usually called dust grains and are of size 10 nm and upwards. Dust comprises about 1% by mass of interstellar matter. It extinguishes and reddens starlight, and can also be detected by its absorption and emission of infrared radiation and by its polarizing effect on starlight. The exact composition of interstellar dust is uncertain: silicates, graphite, and carbides are among the components identified through infrared absorption measurements. Dust may account for the diffuse interstellar bands in the optical spectra of stars. Dust is produced in the cool outer envelopes of red-giant stars, in novae, and in supernovae. Dust is also present in the Solar System as interplanetary dust and cometary dust. Some dust is driven out of the Solar System by the radiation pressure of the Sun’s light, while new dust is generated by asteroid collisions and the break-up of comets. See also Grains, Interplanetary; Grains, Interstellar.