Debris disks are dusty , gas-poor disks around main sequence stars ( Backman & Paresce 1993 ; Lagrange , Backman & Artymowicz 2000 ; Zuckerman 2001 ) .
Micron-sized dust grains are inferred to exist in these systems from measurements of their thermal emission at infrared through millimeter wavelengths .
The estimated lifetimes for circumstellar dust grains due to sublimation , radiation and corpuscular stellar wind effects are typically significantly smaller than the estimated ages for the stellar systems , suggesting that the grains are replenished from a reservoir , such as sublimation of comets or collisions between parent bodies .
Since the color temperature for the excess emission is typically T _ { gr } \sim 110 - 120 K , similar to that expected for small grains in the Kuiper Belt , these objects are believe to be generated by collisions between parent bodies analogous to Kuiper Belt objects in our solar system ; however , a handful of systems possess warm dust , with T _ { gr } \geq 300 K , at temperatures similar to the terrestrial planets .
We describe the physical characteristics of debris disks , the processes that remove dust from disks , and the evidence for the presence of planets in debris disks .
We also summarize observations of infalling comets toward \beta Pictoris and measurements of bulk gas in debris disks .