First of all I'm going to copy and paste a post that Vladimir Romanyuk (Space Engineer) wrote four years ago in the old forum (I think is a very good synthesis of what is coming from GAIA).
Discovering of new objects
- 1 billion stars down to 20m - coordinates, parallaxes (distances), proper motions, radial velocities and low-resolution spectra
- 200 million stars - measurement of radial velocities
- 100 million stars - getting the light curves
- 200,000 new white dwarfs and 50,000 new brown dwarfs (!)
- 500,000 small Solar system bodies with photometry and orbits
- 500,000 quasars with redshifts and photometry
- Measurement of masses of 10,000 stars with an accuracy of <1%
- 10,000 - 20,000 exoplanets within 200 pc (!!!)
- Coordinate measurement accuracy (μas = micro arc second = 10[sup]-6[/sup] seconds of arc)
- 7 μas up to 10m
- 10-25 μas up to 15m
- 300 μas up to 20m
- HIPPARCOS for comparition: 1000 μas up to 12m - Distance with 1% accuracy to about 10 million stars up to 2.5 kpc
- Distance with 10% accuracy to about 100 million stars up to 25 kpc (the diameter of the galaxy!)
- Massive numbers of rare types of stars and rapid evolutionary processes
- Parallax calibration for the distance indicators such as Cepheids and RR Lyrae stars in the LMC / SMC
- Sharp Hertzsprung-Russell diagram throughout the galaxy
- The Mass function and the Luminosity function of the solar neighborhood stars
- - including ~200,000 ~ white dwarfs and 50,000 brown dwarfs
- The Initial mass function and Luminosity function for the star-forming regions
- The Luminosity function for the Pre-Main-Sequence stars
- Detection and collection of data about stars of all spectral types and all types of galactic population
- Detection and investigation of variability of stars of all spectral types
- Distribution of distances and velocities of all stellar populations in the Galaxy
- Spatial and dynamic structure of the disk and halo of the Galaxy
- Formation history of the Galaxy
- Huge statistics - a strict basis for the theory of stellar structure and evolution
- At least 70 measurements of coordinate for 100,000 stars of F, G, K types up to 200 pc
- Detection of 10,000 - 20,000 exoplanets with astrometric method (~ 10 per day!)
- Detection of ~5000 exoplanets by transit method (!)
- Orbits of detected planets for ~5000 systems
- Detection limits:
~ 1 Jupiter mass with a period of <10 years within 200 pc
~ 10 Earth masses within 10 pc - Complete catalog of all the planets with a period of 2-9 years for all types of stars (!)
- True masses of the planets, not the lower limit of the mass (M, not M*sin(i))
- Relative inclinations of the orbits in multiplanetary systems
- Refinement of parameters of Kepler exoplanets and candidates - thanks to refinement of stellar parameters
- Deep (up to 20m) and uniform whole sky survey and detection of moving objects
- 10[sup]5[/sup]-10[sup]6[/sup] of new objects (only 340,000 are known for now!)
- Study of change of taxonomy/mineralogical composition with heliocentric distance
- Diameters for ~1000 objects, masses for ~100 objects
- Orbits - 30 times better than present, even after 100 years
- Trojan asteroids for Mars, Earth and Venus
- Kuiper Belt Objects: ~ 300 up to 20m (including binaries and Plutinos)
- Near-Earth objects - Cupids, Apollos and Athenas (currently known - 1775, 2020 and 336 respectively)
- ~1600 crossing Earth orbit asteroids with diameter > 1 km (currently known - 100)
Asteroid Gaia-606 (one of the firsts discovered by the mission)
Confirmation of the General Relativity
- Gravitational deflection of light in the gravitational field of the planets
- Precession of the perihelion of asteroids orbits
- Astrometric fluctuations of satellites of known stellar black holes