  We show for the first time how to conduct a direct search for dark matter
using Gaia observations. Its public astrometric data may contain the signals of
mirror stars, exotic compact objects made of atomic dark matter with a tiny
kinetic mixing between the dark and SM photon. Mirror stars capture small
amounts of interstellar material in their cores, leading to characteristic
optical/IR and X-ray emissions. We develop the detailed pipeline for conducting
a mirror star search using data from Gaia and other stellar catalogues, and
demonstrate our methodology by conducting a search for toy mirror stars with a
simplified calculation of their optical/IR emissions over a wide range of
mirror star and hidden sector parameters. We also obtain projected exclusion
bounds on the abundance and properties of mirror stars if no candidates are
found, demonstrating that Gaia is a new and uniquely powerful probe of atomic
dark matter. Our study provides the blueprint for a realistic mirror star
search that includes a more complete treatment of the captured interstellar gas
in the future.
