The stars Gaia hunter on its launch pad - Le Figaro

A Russian Soyuz rocket must carry the European telescope to map a billion stars in 2020.

Gaia will take off on Thursday. Space Telescope European Space Agency (ESA) launched aboard a Soyuz rocket from Kourou, French Guiana. If all goes well, the spacecraft will deploy its two tons petals, a shield that should protect it from sunlight, a good hour after takeoff. And Gaia will start scanning the sky thirty days later, when it reaches the second Lagrange point, an equilibrium position in the solar system located 1.5 million kilometers beyond the Earth.

goal is not to make beautiful images, like Hubble, but to measure the distance that separates us more than a billion stars, or 1% of our Milky Way. “It may sound surprising, but we do not know the precise position as a relatively small number of stars,” says François Mignard, an astronomer at the Observatoire de la Côte d’Azur and one of the scientists responsible for the mission Gaia. In this one simple reason: nothing looks more like a bright star located far a much duller nearest star! In other words, it is not obvious to estimate the distance of a star from its simple brilliance.

The most reliable method that will be implemented by Gaia is a geometric calculation. “It will measure 70 times the position of each star at different times, explains François Mignard. As the Earth moves between two measurements, we will be able to deduce the apparent motion of the star’s speed and distance that separates us. “Finer mechanical understanding of our galaxy is the key.

In the late 1990s, Hipparcos satellite allowed cataloged 100,000 stars by this method. It was certainly remarkable, but Gaia should identify 10,000 times! This represents 40 gigabytes of data daily (twenty high-definition movies) for at least five years (if necessary, the satellite will operate one more year). After an additional two years of treatment, or in 2020, astronomers should be able to reconstruct 3D maps of the Milky Way by reproducing the movements of each of the billion stars. From autumn 2015, a first interim catalog will be published and made available to the scientific community.

“We did not choose the one billion figure because it was pretty, says François Mignard. Instead, we reasoned sensitivity necessary to obtain a good sample of our galaxy regardless of the distance at which we look. It turns out that this requires a discerning stars shine 400,000 times smaller than a star visible to the naked eye. “

Gaia is a monster of technology. It is equipped with a huge focal plane consists of a billion pixels. Ten mirrors of the telescope – the largest measuring 3.50 m – are silicon carbide, an extremely light and very sensitive to temperature variations innovative ceramics. It is a specialized French SMEs Boostec, who produced.

order not to disrupt the highly accurate geometrical measurements that is capable of performing, engineers have hunted all sources of spurious vibrations. These are tiny thrusters and four cold gas, capable of infinitesimal flare, which will guide Gaia, rather than flying traditional inertia. At their lower operating power, it would take a million of these thrusters to levitate an apple! Even communication antennas Gaia are immobile to avoid any disturbance.

“This has been our great industrial and technological challenge,” says Eric Beranger, CEO of Astrium Satellites, the company responsible for the design and manufacture of the telescope. However, these innovations come at a cost: the total mission budget is estimated at one billion euros, including launch. Besides the stellar census, Gaia will detect thousands of asteroids in the solar system, including those that exist may be between the Earth and Sun. The telescope could also flush thousands of extrasolar planets by an unpublished method: the astrometric technique. This is to identify the small side of a star related to the attraction of the gas giants that revolve around him oscillations. This detection principle is very old, but Gaia is the first instrument to have the sensitivity required to detect movements as small. Astronomical hunt is on.