  Extrapolating from the solar system's asteroid belt, we propose that
externally-contaminated white dwarfs without an infrared excess may be
experiencing continuous accretion of gas-phase material that ultimately is
derived from the tidal destruction of multiple small asteroids. If this
scenario is correct, then observations of metal-polluted white dwarfs may lead
to determining the bulk elemental compositions of ensembles of extrasolar minor
planets.
