Gaia is a global space astrometry mission, and a successor to the ESA Hipparcos mission. Part of ESA's long-term scientific programme, Gaia is being built by EADS Astrium and is expected to be launched in 2012 on a Soyuz vehicle. Gaia will be placed in orbit around the Sun, at a distance of 1.5 million kilometres further out than Earth, at the L2 Lagrangian point of the Sun-Earth system. It will conduct a census of a billion stars in our galaxy, monitoring each of its target stars about 100 times over a five-year period, precisely charting their distances, movements, and changes in brightness. It is expected to discover hundreds of thousands of new celestial objects, such as extra-solar planets and failed stars called brown dwarfs. Within our own solar system, Gaia should also identify tens of thousands of asteroids.
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