Another is to determine the structure of the plumes of dark matter, the invisible and still unknown component of matter in which galactic matter is immersed.

One approach is to map, on cosmic scales, the way in which galaxies organise themselves into long filaments, forming what specialists call the “cosmic web”. Practically speaking, there are various ways in which the nature of dark energy might be pinned down.

On the other hand, its effects on the large-scale organisation of matter in the Universe can be observed, and its properties inferred, just as the morphological characteristics of a suspect can be deduced from their footprints.

The problem is that scientists have no idea what it is. Dark energy is invisible, elusive, and impossible to observe directly or capture on the sensitive surface of a detector. However, repeated observations pointed to an unavoidable conclusion: it was as if the Universe were filled with a type of energy of unknown nature that, by opposing gravity, was causing it to expand ever faster.Īccording to the data, this energy, whose indirectly inferred properties bear no resemblance to any known matter, is even thought to account for some 70% of the total energy content of the Universe. Yet to everyone's amazement, the astrophysicists concluded that expansion had in fact entered a phase of acceleration which no one could explain. At the time, two independent teams were wondering whether the Universe, under the effect of gravity, would see its expansion slow down indefinitely, or whether it would eventually experience a phase of contraction that would bring it back to its original state. Accelerating expansionĭark energy has fascinated the world of cosmology ever since 1998. The hope is to determine exactly what is causing the expansion of the Universe to accelerate – a fact that, for want of a better explanation, scientists attribute to a mysterious phenomenon dubbed “dark energy”, about which they understand absolutely nothing. The mission's goal is to scrutinise some two billion galaxies over the next six years, with the aim of drawing up the first 3D map of the cosmos out to a distance of 10 billion light years.

“We're all very excited, this is a truly incredible moment,” says Stéphanie Escoffier 1, who heads Euclid-France. For the approximately 1,500 researchers, engineers and technicians involved in this extraordinary scientific venture, which has been over ten years in the making, the launch marks the beginning of the operational phase. Shortly after 5:00pm CEST on Saturday 1 July 2023, the European Space Agency's (ESA) Euclid spacecraft lifted off from Cape Canaveral, Florida (US), on a SpaceX Falcon 9 launch vehicle, heading towards its observation orbit 1.5 million kilometres from Earth.

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