This animation shows the evolution of a planet-forming disc around a star. Initially, the young disc is bright and thick with dust, providing raw materials for building planets. In the first 10 million years or so, gaps appear within the disc as newborn planets coalesce out of the dust, clearing out a path.
In time, this planetary "debris disc" thins out as gravitational interactions with numerous planets slowly sweep away the dust. Steady pressure from the starlight and solar winds also blows out the dust. After a few billion years, only a thin ring remains in the outermost reaches of the system, a faint echo of the once-brilliant disc.
Our own solar system has a similar debris disc – a ring of comets called the Kuiper Belt. Leftover dust in the inner portion of the solar system is known as "zodiacal dust."
Bright, young discs can be imaged directly by visible-light telescopes, such as NASA's Hubble Space Telescope. Older, fainter debris discs can be detected only by infrared telescopes like NASA's Spitzer Space Telescope, which sense the discs' dim heat.
Animation Credit: NASA/JPL-Caltech/T. Pyle/ssc