Exozodiacal dust is 1–100 micrometre-sized grains of amorphous carbon and silicate dust that fill the plane of extrasolar planetary systems. It is the exoplanetary analog of zodiacal dust, the 1–100 micrometre-sized dust grains observed in the solar system, especially interior to the asteroid belt. As with the zodiacal dust, these grains are probably produced by outgassing comets, as well as by collisions among bigger parent bodies like asteroids. Exozodiacal dust clouds are often components of debris disks that are detected around main-sequence stars through their excess infrared emission. Particularly hot exozodiacal disks are also commonly found near spectral type A-K stars. By convention, exozodiacal dust refers to the innermost and hottest part of these debris disks, within a few astronomical units of the star. How exozodiacal dust is so prevalent this close to stars is a subject of debate with several competing theories attempting to explain the phenomenon. The shapes of exozodiacal dust clouds can show the dynamical influence of extrasolar planets, and potentially indicate the presence of these planets. Because it is often located near a star's habitable zone, exozodiacal dust can be an important noise source for attempts to image terrestrial planets. Around 1 in 100 stars in the nearby solar systems shows a high content of warm dust that is around 1000 times greater than the average dust emission in the 8.5–12 μm range.
