2023-07-01 05:30:13
Electromagnetic compatibility tests are carried out before the launch of the Euclid mission, in a special room at the Thales Alenia Space test facilities, in Cannes (Alpes-Maritimes), in February 2023. MANUEL PEDOUSSAUT / ESA
The central character of the first two trilogies Star Wars is called Darth Vader. In the French version, Star Warsit was translated into Darth Vader, as if this “Dark” – “dark” in English – was to reinforce the dark side of the Force in which this former Jedi knight, dressed all in black, sank.
Dark is also the adjective that qualifies two of the most important elements of current cosmology, the dark matter and the dark energy, in French “dark matter” and “dark energy”. The first ensures the cohesion of galaxies and galactic clusters while the second is responsible for the accelerated expansion of the Universe; between them, they represent 95% of the content of the latter.
qualify them as “‘Dark’ is a way of saying that we don’t know what it is, that their nature is unknown to us”, admits Giuseppe Racca, responsible for the Euclid mission of the European Space Agency (ESA). It is to take off on Saturday July 1 from the Kennedy Space Center in Florida on a SpaceX Falcon-9 rocket. With the aim, precisely, of lifting the veil on the dark side of the cosmos.
To carry out this crucial mission, the Euclid satellite – two tonnes, 4.7 meters high, 3.5 meters on a side – will position itself around the Lagrange 2 point, a point in space located 1.5 million kilometers from Earth, where the gravitational influences of the Sun and our planet are such that a craft remains there in a stable position. This is already where the James-Webb Space Telescope is located. Like him, Euclid will systematically turn his back on our star, both to recover energy, thanks to a large solar panel that lines his back, and to keep his instruments in the shade and cool.
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What is this satellite going to watch? The difficulty of the project lies in the fact that what the scientists want to characterize – the distribution of dark matter, which emits no light, and the dilation of space – cannot be seen.
Euclid is therefore a machine for revealing the invisible. How ? Imagine that someone holds a balloon made of a perfectly transparent balloon in their mouth, which represents space, suggests David Elbaz, astrophysicist at the CEA: “It is very difficult to know if the balloon is inflating or not. To determine this, I will therefore take a marker and draw small black lines on the ball. If I see them moving apart, I’ll know it’s inflating and how fast, and if I see them getting closer, I’ll know it’s deflating. »
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