This animation shows the evolution of a planet-forming disk around a star.
Initially, the young disk is bright and thick with dust, providing raw
materials for building planets. In the first 10 million years or so, gaps
appear within the disk as newborn planets coalesce out of the dust,
clearing out a path.
In time, this planetary "debris disk" 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 disk.
Our own solar system has a similar debris disk -- 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 disks can be imaged directly by visible-light telescopes,
such as NASA's Hubble Space Telescope. Older, fainter debris disks can be
detected only by infrared telescopes like NASA's Spitzer Space Telescope,
which sense the disks' dim heat.
