Gaia satellite, a cartographer of the Milky Way

It is the height from which one embraces the landscape. The tree that dominates the forest… The third delivery of the Gaia Space Astrometry mission marks a new turning point in the study of the formation, formation and evolution of our galaxy.

This European Space Agency (ESA) satellite, launched in 2013, systematically analyzes light from the brightest objects in the sky to produce a 3D map of about 1% of the Milky Way. On June 13, it took the decisive step of presenting the first complete copy of its catalog to the scientific community. In total, 1.8 billion stars and millions of other objects, which managed to determine not only the location on the celestial vault and the distance, but also, for a certain number of them, speed or physical properties.

This survey is far beyond all that has been done in the field of astronomy, the branch of astronomy devoted to measuring the position and motion of stars. “The previous stock, the inventory of the European Space Agency’s Hipparcos mission, between 1989 and 1993, barely covered 120,000 of the 200 billion stars in our galaxy.”recalls François Menard, scientific director of Gaia France.

It’s also a real tour. To successfully place objects on the vault with an accuracy of 7 to 30 microseconds of arc, equivalent to the angle under which a hair thickness can be seen at 1,000 km, Gaia, a satellite designed and produced under the contracting authority of Astrium (former name of the Astrium Systems branch SpaceX on Airbus-DS) scans the sky with two telescopes paired with an array of ultra-sensitive CCD detectors for a period of thirty-four months.

During this period, using his three instruments – astronomical, spectroscopic, and spectroscopic – he analyzed at least seventy times the light from each source, and collected a quantity of information on the order of several petabytes, unique in the history of astronomy. Once on Earth, this vast amount of raw data, comparable only to that produced (over the course of one year) by the LHC particle physics experiments at CERN, Geneva, was processed in six computing centers, including the one at The National Center for Space Studies (CNES) in Toulouse; They were then cataloged, abstracted, and curated within a European Union of 430 scientists, including one hundred French.

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