Gaia (spacecraft)

Gaia (spacecraft)

Gaia (originally an acronym for Global Astrometric Interferometer for Astrophysics) is a European Space Agency (ESA) space mission in astrometry to be launched in October 2013. Successor to the Hipparcos mission, it is part of ESA's Horizon 2000 Plus long-term scientific program. The mission aims to compile a catalogue of approximately 1 billion stars, or roughly 1% of stars in the Milky Way. It will monitor each of its target stars about 70 times to a magnitude 20 over a period of 5 years. Its objectives comprise:

• determining the positions, distances, and annual proper motions of 1 billion stars with an accuracy of about 20 µas (microarcsecond) at 15 mag, and 200 µas at 20 mag
• detection of tens of thousands of extra-solar planetary systems
• capacity to discover Apohele asteroids with orbits that lie between Earth and the Sun, a region that is difficult for Earth-based telescopes to monitor since this region is only in the sky during or near the daytime
• detection of up to 500,000 distant quasars
• more accurate tests of Albert Einstein’s general relativity theory

Gaia will create an extremely precise three-dimensional map of stars throughout our Milky Way galaxy and beyond, and map their motions which encode the origin and subsequent evolution of the Milky Way. The spectrophotometric measurements will provide the detailed physical properties of each star observed, characterising their luminosity, effective temperature, gravity and elemental composition. This massive stellar census will provide the basic observational data to tackle a wide range of important problems related to the origin, structure, and evolutionary history of our Galaxy. Large numbers of quasars, galaxies, extrasolar planets and Solar System bodies will be measured at the same time.

Arianespace expects to launch Gaia for ESA in August 2013, using a Soyuz rocket from its Guiana Space Centre (GSC) in French Guiana. It will be operated in a Lissajous orbit around the Sun–Earth L₂ Lagrangian point.