Low-density dust or gas that fills the space in a planetary system around or between the planets. Most interplanetary matter in the inner solar system is dust created by collisions among asteroids or released by comets as they pass by the Sun. Ionized gas, launched at high speeds from the Sun as the solar wind, also permeates the solar system and creates a variety of important electromagnetic effects where it interacts with planets. Viewed from a nearby star, the interplanetary matter around the Sun would outshine the Earth. Recent detections of large quantities of similar material around other stars—many of which appear to harbor planets—have rekindled widespread interest in this subject.