Still, as soon as the mission design was firmly established, it was realized that the scientific case for two-dimensional observations of high-surface brightness regions with GAIA was potentially dramatic. Although such an idea came up relatively late in the course of the misssion feasibility studies, it was soon integrated in the mission baseline design under the name of GAIA Galaxy Survey.
Accurate positional measurements and high-resolution, multi-color photometric
observations of the inner regions of about 3 million galaxies are unique
datasets GAIA could provide with only a minimum effort in terms of mission
design and telemetry.
Owing to the late inclusion of galaxy observations in the mission design,
it has not yet been possible to consider in detail the wide-ranging scientific
objectives that could thus be addressed, and the objectives that are here
briefly mentioned are therefore to be considered a minimum.