Final preparations are under way to launch a space telescope that aims to produce the largest, most accurate 3D map of the cosmos and unravel the dark forces that shape it.
The European Space Agency’s €1bn (£862m) Euclid probe will observe more than a third of the sky and billions of galaxies to shed light on the mysterious dark matter and dark energy that together account for 95% of the universe.
“It’s one of the biggest questions in science,” said Prof Isobel Hook, an astrophysicist on the mission at Lancaster University. “We don’t know what the whole fabric of the universe is and that is huge. It’s our origins. It’s fundamental.”
Barring last-minute glitches, Euclid will embark on a one-month journey to its vantage point 1m miles from Earth when it blasts off on a Falcon 9 rocket from Cape Canaveral in Florida at 11.11am local time (1611 BST) on Saturday.
The spacecraft was previously scheduled for takeoff in 2022 on a Russian Soyuz rocket, but the invasion of Ukraine marked the end of cooperation between the ESA and the Russian space agency, Roscosmos.
“There’s a real buzz, it’s amazing,” Hook said. “This time last year, we didn’t know how the launch was going to go ahead.” More than 2,000 European scientists are involved in the mission.
Named after Euclid of Alexandria, the ancient Greek founder of geometry, the spacecraft is bound for a halo-like orbit around a spot known as the sun-Earth Lagrange point two. The location, shared with the James Webb space telescope, allows the two-tonne probe to keep its back to the sun, shielding its sensors as it stares into the void.
Euclid carries a 1.2-metre-diameter telescope and two scientific instruments: an optical camera (Vis) and a near-infrared spectrometer and photometer (Nisp). While dark matter and dark energy are invisible, astronomers infer the existence of dark matter from the gravitational pull it exerts on galaxies, and see dark energy at work in the accelerating expansion of the universe.
The six-year mission aims to map precisely how dark matter clumps around galaxies and lays the foundations for the cosmic web of matter that stretches through the universe.
One way dark matter reveals itself is through weak gravitational lensing, whereby the mass of the invisible substance warps spacetime. The effect causes light to bend as it travels from galaxies to the telescope, producing subtle distortions in their shapes. By analysing the distortions of galaxies at different times and distances, scientists can infer where dark matter lurks and how dark energy has shaped the evolution of the cosmic web.
The Vis camera, developed by a team at University College London, is central to the Euclid mission and will observe more of the universe in one day than the Hubble space telescope did in 25 years.
Astronomers knew about the expansion of the universe in the 1920s but only in the 1990s did researchers, including Hook, find evidence that it was accelerating. Scientists proposed dark energy as a mysterious anti-gravity force that ramped up in the past 6bn years, causing galaxies to fly away from one another at an ever-increasing rate.
To learn more about the nature of dark energy, Euclid scientists will measure the distances to millions of galaxies and look at how they are distributed through space. Today, pairs of galaxies tend to be separated by 490m light years, but looking at the standard separation through cosmic history will show how space has stretched over time. “We might confirm that dark energy is constant,” Hook said. “But it may not be constant, and we find that it’s not – that’s a very big discovery.”
While everyday objects such as stars and cars are made from atoms, dark matter is thought to comprise exotic new particles that barely interact with normal matter. Numerous detectors around the world are searching for the mysterious substance but so far, all have drawn a blank.
Dark energy is more mysterious still: scientists have no idea whether the anti-gravity force comes from quantum particles popping in and out of existence in the vacuum, an entirely new particle field, or if Einstein’s theory of general relativity is simply wrong.
Precision measurements from Euclid should help scientists work out which of the many dark matter and dark energy theories most effectively describe reality. “It’s a fundamental problem to be in 2023 and not know what this large fraction of the universe is made of,” said Prof Mark Cropper, the leader of the Vis team at UCL’s Mullard space science laboratory. “We have lots of theories but it’s hard to make progress without data. It’s like being in the dark ages.”
