GAIA is a project of the European Space Agency (ESA), the satellite was launched December 19, 2013 from French Guiana with a Soyuz rocket. The mission objective, mapping 3D Milky Way, with a precision of up to 7 arc microseconds or 7/3600e degree for the brightest stars (magnitude 12 or less) to 300 microseconds of arc for the fainter stars (magnitude 20). This will enable scientists to collect data over a billion objects and to better understand the mechanisms of formation of galaxies, the inner workings of stars, the influence of the dark matter and the bending of light rays due to the effects gravitational.
The probe 2 tons, has three detectors mounted on one of the two telescopes, which may be about 75 measures astrometric, spectroscopy of photometry to each object observed. It will report the position, speed, brightness and distance from Earth of each star pointing by its telescopes. GAIA is the surveyor of the Galaxy, the probe will send for 5 years, more than a petabyte of data (1000 TB) to be processed by CNES and 30 international laboratories. Through the census apply of all these stars, astronomers can identify different generations of stellar populations, and restore their path in space and time. The aim is to produce the most detailed image possible to the structure of our Galaxy and predict its evolution.
Records of unparalleled precision will feed scientists for decades. GAIA is able to measure the thickness of a hair located 1000 km away. To measure the distance of stars GAIA uses the method of stellar parallax. This ancient geometrical method consists in seeking the star twice, six months apart. In other words, astronomers measure the parallax angle by measuring the position of a star from a position of Earth in its orbit and measure again, six months later, when the Earth is on the other side of the Sun, then it has traveled 300 million km. More star is closer, more the parallax angle is large, this angle gives us directly the distance of the star. By knowing the distance of a star, we can determine its main features, its actual brightness, age, weight, temperature. This will require permanently know the distance between the two windows of shooting and therefore to know precisely the position of GAIA.
Continuous monitoring from the ground floor will be ensured by a network of telescopes in order to position GAIA hundredth of a second of arc, this means that the satellite will remain confined within a radius of 100 meters. This device, called GBOT (Ground Based Optical Tracking), complements the radio ESA methods.
In a small bubble 12 light years in diameter centered on the Sun, there are already 31 stars. But as soon as GAIA will pointed its two telescopes of silicon carbide, to faraway distances of the order of 30,000 light years, it can detect hundreds of thousands of stars and even exoplanets the size of Jupiter.
GAIA will detect 1000 to 2000 Cepheids in the Milky Way, as the distance is perfectly known, it will accurately calibrate the measurement method. The European probe will also examine nearly 500,000 quasars and observing large-scale movement of stars, Gaia will show the distribution of dark matter. Maybe its measures provide answers to one of the major problems of modern astrophysics, the nature of most of the matter in the universe.
Thanks to the high precision of the probe, the scientific measurement of Gaia will test more finely general theory of relativity of Einstein. It is probable that usually invisible gravitational effects appear in the data.
And finally, thanks to the precision of the photometric and astrometric measurements, Gaia will see thousands of exoplanets by the transit method because each object must be seen dozens of times during the mission. The computing power required to process all data is estimated at 6 teraflops (6,000 trillion operations per second).
The volume of data to be processed will be in the order of a million billion bytes, capacity 250,000 DVD. Gaia will observe deep sky on a special orbit around the Sun. This special location is the L2 Lagrange point. The L2 point is a great place to observe the universe as it is an extremely stable thermal environment. It is located 1,492,000 km of Earth on the line defined by the Earth and the Sun. Since 2009, is located on this orbit, the satellite Herschel and Planck Surveyor. This Lagrange point L2, following the Earth while we orbit around the Sun, as well the Sun, the Earth and the Moon are still outside the visual field instruments.
Image: The Gaia satellite, built in Toulouse (France) by Astrium. In ancient Greece in the second century BC, Hipparchus of Nicea (-190 to -120 BC. JC) carefully measured to the naked eye, the position of more a thousand stars. Hipparchus produced the first star catalog. Hipparcos (HIgh Precision PARallax COllecting Satellite), the first astrometry satellite (1989-1993), provided the celestial coordinates of some 120 000 stars with an accuracy 10 to 100 times greater than previous catalogs, established the using ground-based instruments. After the Hipparcos satellite, it is the turn of GAIA, the surveyor, to measure the Galaxy with much larger mirrors, and map in 3D over a billion objects (stars, planets, pulsar, quasars...). With Soyuz, Ariane 5 and Vega all operating from the Guiana Space Center, Arianespace is the only launch services provider in the world capable of launching all payloads into all orbits, from the largest to the smallest geostationary satellite, as well as clusters of satellites for constellations and missions to support the International Space Station (ISS).