The Galactic census project

Name Gaia was originally derived as an acronym for Global Astrometric Interferometer for Astrophysics. This reflected the optical technique of interferometry that was originally planned for use on the spacecraft. However, the working method has now changed. Although the acronym is no longer applicable, the name Gaia remains to provide continuity with the project.

Description Gaia is a mission that will conduct a census of a thousand million stars in our Galaxy. It will monitor each of its target stars about 70 times during a five-year period, precisely charting their positions, distances, movements, and changes in brightness. Gaia 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 observe hundreds of thousands of asteroids.

Launch 2013, on a Soyuz-Fregat rocket from Sinnamary, part of Europe’s Spaceport in French Guiana.

Status Under development, in the manufacturing and test phase, with EADS Astrium SAS (Toulouse) as prime contractor.

Orbit Gaia will map the stars from its orbit around the second Lagrangian point, L2. This special location, 1.5 million km further from the Sun than Earth, keeps pace with Earth’s yearly revolution around the Sun and thus maintains the positions of the Sun, Earth and spacecraft on a single line. This choice minimises any obstructions caused by the Sun and Earth falling within Gaia’s fields of view.

Notes Gaia's measurements will be so accurate that, if it were on Earth, it could measure the thumbnails of a person on the Moon.

Gaia’s transmitter is weak, much less powerful than a standard 100 W light bulb. Even so, this equipment will be able to maintain the transmission of an extremely high data rate (about 5 Mbit/s) across 1.5 million km. ESA’s most powerful ground stations, the 35 m-diameter radio dishes in Cebreros, Spain, and New Norcia, Australia, will intercept the faint signal transmitted by Gaia.

The numbers foreseen in Gaia's celestial census are breathtaking. Every day it will discover, on average, 10 stars possessing planets, 10 stars exploding in other galaxies, 30 ‘failed stars’ known as brown dwarfs, and numerous distant quasars, which are powered by giant black holes.

Estimates suggest that Gaia will detect about 15 000 planets beyond our Solar System. It will do this by watching for tiny movements in the star’s position caused by the minute gravitational pull of the planet on the star.

Gaia will test Albert Einstein’s General Theory of Relativity to the limits by checking the perturbing effect of the Sun’s gravity on starlight to about two parts in a million.