White Dwarf Debris Disks: The Fate of Planetary Systems?

White dwarfs may offer new insights into how common extrasolar minor bodies such as asteroids are. One quarter of all white dwarfs appear to have heavy elements such as Ca, Mg, Si, and Fe in their atmospheres, despite the fact that the extreme gravity of these stars causes heavy elements to sink through their atmospheres on a timescale of weeks to years. These white dwarfs are currently accreting from their circumstellar environments, and we argue that they are all accreting from debris disks left over from tidally disrupted asteroids, comets, or other minor rocky bodies. This interpretation leads to the tentative conclusion that >= 25% of all stars have planetary systems composed of at least minor, rocky bodies.