Abstract

Debris disks around main-sequence stars are believed to derive from planetesimal populations that have accreted at early epochs and survived possible planet formation processes. Being stirred by the largest embedded bodies and/or giant planets, these planetesimals undergo a collisional cascade that grinds them to smaller objects of all sizes down to tiny dust, until the latter is removed by direct radiation pressure, drag forces, and various erosive processes. I will briefly review essential physics of debris disks and modeling methods. I will then concentrate on the central question of debris disk studies: how do observations of debris dust, interpreted through collisional and dynamical models, constrain the invisible planetesimals, known or alleged planets in the systems, and the history of planetesimals and planets? Specifically, what can we learn about the current mass, location, extension, and dynamical excitation of planetesimals, optical and mechanical properties of solids, and the collisional processes that grind them to dust? To what extent can we infer the initial size distribution of the planetesimal belt at the onset of the collisional cascade and find out what and when may have ignited it? These questions will be addressed from the perspective of (i) the observed statistics of a large number of unresolved debris disks, (ii) SEDs of individual unresolved systems, and (iii) detailed datasets on selected resolved disks.