• In Cannes, in the clean rooms of Thales Alenia Space where it was assembled, the Euclid satellite is ready to take off to carry out a 3D mapping of some two billion galaxies.
  • This mission of the European Space Agency is dedicated to improving knowledge about dark matter and dark energy, which are still very poor even though they constitute 95% of the Universe.
  • If the first images of Euclid are expected this fall, the first results of their analyzes, they will not fall for a year and a half.

Names have been found for them, it is estimated that they constitute 95% of the universe and yet we know almost nothing about them. They are dark matter and dark energy. Considered far too mysterious for the taste of the scientists whose theories and fantasies they have been feeding for a few decades.

"All we know is that the former has gravity and the latter causes the universe to expand rapidly," said Giuseppe Racca of the European Space Agency (ESA). Their exact nature remains unknown and, given their preponderance, it is a real "cosmic embarrassment", says the head of the mission that ESA is preparing to launch to unravel its secrets. In Cannes, in the clean rooms of Thales Alenia Space where it was assembled, the Euclid satellite is ready to take off. It is expected to fly this summer and remain in orbit for at least six years to carry out a 3D mapping of some two billion galaxies.

And it is this mass of new information, analyzed by hundreds of scientists, that should advance our knowledge in this area... crotchet. How? And what are the possible revelations? 20 Minutes went to interview some of these specialists at the manufacturer, near the Croisette, where they were meeting this week.

What will this 3D mapping of two billion galaxies be used for?

With this €1.5 billion mission, the European Space Agency hopes to answer at least two questions: "What is the origin of the universe?" and "why is it expanding at an accelerated rate instead of slowing down due to the gravitational pull of matter?" And for that, "the big advantage of Euclid lies precisely in the number of galaxies that can be observed," explains Stéphanie Escoffier, director of research at the CNRS. "We will multiply it by ten and inevitably, the more there are, the more accurate our results can be. This 3D mapping should be a real revolution," she continues.

For comparison, the Hubble Space Telescope has observed the sky over 25 square degrees (a unit of measurement of space as seen from Earth) in 25 years while the new satellite will be able to capture ten square degrees per day! "We will be able to study the distribution of these galaxies in a very precise way, which will tell us about dark energy, but also analyze their deformation, which can give us information on the location of dark matter," says the researcher.

Scientists should therefore be able to apprehend this "invisible" by quantifying its absence. Are you following? They will rely on the effect of "gravitational lensing", that is to say when a celestial object deflects the rays emitted by a light source, to "measure the amount of matter between the satellite and the observed galaxy".

How will the mission work?

Launched from Cape Canaveral, aboard a SpaceX Falcon 9 rocket, next July, Euclid should arrive at its destination in October. From its heliocentric orbit, that is to say around the sun, 1.5 million kilometers from the Earth, the telescope will relentlessly photograph the depths of the cosmos until 2029, and perhaps beyond, if all goes well. Equipped with an impressive sensor of more than 600 million pixels, the craft will provide images "in which we will be able to zoom almost to infinity," explains Pierre Casenove, in charge of the program for CNES, the National Center for Space Studies. To target this or that galaxy.

That will be for the visible part. A second device, a "near-infrared spectro-imager and photometer", will then allow "cosmologists to estimate the distance that separates us from the galaxy in question", describes Thales Alenia space. It is therefore thanks to him that the mapping obtained will be modeled in 3D.

Assembled in Cannes, the Euclid space telescope is expected to be launched this summer from Florida, aboard a Falcon 9 rocket from @SpaceX, on the trail of dark matter and dark energy (Thales Alenia space images) pic.twitter.com/GgRVJH0OXx

— Fabien Binacchi (@fabienbinacchi) February 25, 2023

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The result is barely imaginable amounts of information that will be distributed across several data centers in Europe. "We will have to process 26 petabytes per year," or 26,000 Terabytes "and, for comparison, the Hubble satellite is 160 terabytes each year," says Giuseppe Racca, mission leader at the European Space Agency (ESA). "We can't wait, but also a little scared. We will have to face a monster of data, "also warns the French astrophysicist David Elbaz, director of research at the Atomic Energy Commission (CEA). The latter is part of a consortium of 1,500 scientists (in sixteen countries) who will have to dissect everything.

What can we expect from these results?

Euclid will scan the sky through space but also time. The craft, named in honor of the mathematician considered the "father of geometry", will be able to capture light that took up to ten billion years to reach it. "We will be able to see if dark energy is a cosmological constant, if it is something that will evolve over time or if we have to question Einstein's general relativity," says Stéphanie Escoffier. Just that.

And what Euclid could allow to discover already fascinates David Elbaz. "This mapping could allow us to deduce what is at the origin of our own origins. Is everything born with gravity as we know it, with the apple falling from the tree? Or is it that when I put this apple very, very far from the Earth and I drop it, it does not do the same, or even it bars and it even goes back, "says the specialist, with a small idea of the answer. "Some distant objects that we observe, instead of collapsing on top of each other, repel each other. This is analogous to what is known as anti-gravity. »

But then what creates this anti-gravity? All the theories considered on this subject will be able to be tested with this ESA mission. To characterize the still very mysterious nature of dark energy, responsible for accelerating the expansion of the Universe. "Is it a 'property' of space, according to Einstein's answer? Is it the quantum vacuum, as others say? Or is it another crazy possibility, where this energy, called phantom energy, is going to break up galaxies, then stars, then molecules, then atoms, everything you had with the Big Bang. Where she will undo everything again until there is nothing left. Not even a hydrogen atom. If the first images of Euclid are expected this fall, the first results of their analyzes will not come for a year and a half.

  • Sciences
  • Nice
  • Alpes-Maritimes
  • PACA
  • Cannes
  • Space
  • Satellite
  • Universe
  • ESA