Planetary Group Seminar: Debris disks: Comets, asteroids, and dust around stars (A. Krivov)

While planets are the most treasured outcome of the planet formation process, they are not the sole component of planetary systems.  Our solar system harbors numerous comets and asteroids, which represent left-over material that failed to grow into full-sized planets. Furthermore, the solar system is immersed in an ethereal sheet of dust that is continually replenished by these small bodies as a result of their mutual collisions, as well as tidal and thermal disintegration.  Over the last three decades, a similar view has been emerging for other stars.  The belts of left-over planetesimals and their dust, commonly referred to as debris disks, have now been found to be nearly as common around nearby stars as planets.  Most of the debris disks have been detected by thermal radiation of their dust in excess of the stellar photospheric emission, and about a hundred of dusty Kuiper-belt analogs have been spatially resolved in thermal emission of scattered light.  Also, gas emission has been detected in some of the younger disks and interpreted as outgassing of comets. Unlike in the solar system, the small bodies around other stars are not observable directly, yet some of their properties can be constrained from the observed dust emission through collisional and dynamical modeling.  The same applies to planets.  While possibilities of exoplanet detection techniques still remain very limited, the debris disk structure readily revealed by the resolved images can be used to pinpoint the perturbing planets and, as the debris likely traces the dynamical stability regions, can tell us where there are no planets.  Apart from the cold debris dust stemming from the Kuiper-belt analogs, warm dust is often seen closer to the stars.  This dust may be either a signature of asteroid belts or witness the inward transport from the exo-Kuiper belts.  Unluckily, this `exozodiacal' dust has also been realized as a potential obstacle for the upcoming terrestrial planet searches.  This talk will outline essential observational results on debris disks, summarize their basic physics, and show how the study of debris disks influences our understanding of planetary systems.