  The Gaia spacecraft presents an unprecedented opportunity to reveal the
population of long period (a>1\,au) exoplanets orbiting stars across the H-R
diagram, including white dwarfs. White dwarf planetary systems have played an
important role in the study of planetary compositions, from their unique
ability to provide bulk elemental abundances of planetary material in their
atmospheres. Yet, very little is known about the population of planets around
white dwarfs. This paper predicts the population of planets that Gaia will
detect around white dwarfs, evolved from known planets orbiting main-sequence
stars. We predict that Gaia will detect $8\pm2$ planets around white dwarfs:
$8\pm\,3\%$ will lie inside 3\,au and $40\pm10\,\%$ will be less massive than
Jupiter. As surviving planets likely become dynamically detached from their
outer systems, those white dwarfs with Gaia detected planets may not have
planetary material in their atmospheres. Comparison between the predicted
planet population and that found by Gaia will reveal the importance of
dynamical instabilities and scattering of planets after the main-sequence, as
well as whether photoevaporation removes the envelopes of gas giants during
their giant branch evolution.
