Launched on 19 December 2013, the Gaia satellite is pursuing the colossal task of surveying no fewer than 1 billion celestial objects (stars, exoplanets, etc.) in an effort to map part of our galaxy by estimating their distance from Earth and proper velocity. And that’s not all, for while Gaia will be observing an exceptionally large number of objects, it will also be determining their position with unprecedented accuracy—to within as little as 7 microarcseconds (1 arcsecond equals 1/3,600th of a degree).

With Gaia’s observations, astronomers will lift the veil on the formation, structure and history of the Milky Way. The spacecraft is carrying two optical telescopes that will enable it to precisely position celestial bodies and analyse their light spectrum. Three scientific instruments are riding on the probe: BP/RP (Blue Photometer, Red Photometer), to analyse star properties (temperature, mass, age, etc.); RVS (Radial Velocity Spectrometer), designed to gauge the velocity of celestial bodies; and an astrometer to measure their position.

Scheduled to last a minimum of 5 years, Gaia is the sixth flagship mission of ESA’s Scientific Programme. Data are processed by the Gaia DPAC (Data Processing and Analysis Consortium), a European consortium to which CNES has devoted a lot of technical and human resources. The satellite was built by Airbus Defence & Space (ex-Astrium).