Euclid space telescope: The groundbreaking mission to study dark matter and energy

An artist's illustration showing Euclid in space. (Image credit: ESA, CC BY-SA 3.0 IGO)

The European Space Agency's (ESA) Euclid space telescope successfully blasted off from Cape Canaveral, Florida, on July 1, 2023.  The groundbreaking space telescope will hunt for clues about two of the universe's greatest mysteries: dark matter and dark energy.

Despite making up an estimated 95% of the universe, dark matter and dark energy cannot be detected directly. Instead, scientists observe them in the gravitational warping effects seen in many galaxies across the universe.  Euclid's enormous field of view will significantly expand this search for warped space-time.

Here's everything you need to know about Euclid and its search for the universe's most mysterious components.

What is Euclid?

Named after the ancient Greek mathematician who's considered the "father of geometry," Euclid is a space telescope that is 14.7 feet (4.5 meters) tall and 10.2 feet (3.1 m) in diameter. The telescope is mounted with just two instruments: a near-infrared camera that will measure the distance and brightness of galaxies, and a visible-light camera that will study their shapes.

Taken on their own, Euclid's cameras are common among space telescopes. What makes Euclid groundbreaking is these instruments' field of view, with a third of the entire night sky and over a billion galaxies expected to be cataloged by the time the telescope has finished its planned six years of scanning. The telescope should be able to peer up to 10 billion years into the past — slightly less than the James Webb Space Telescope, which has looked back more than 13 billion years.

A last glimpse of Euclid before it is sealed away inside a SpaceX Falcon 9 fairing for launch. (Image credit: European Space Agency)

Euclid's first images

On July 31, 2023, ESA shared the first images taken by Euclid to test the satellite's two main science instruments.

An image taken with Euclid's Near-Infrared Spectrometer and Photometer (NISP) revealed a dazzling starscape of billions of stars and galaxies. Before reaching the instrument's detector, light from the distant objects passed through a filter that splits the light of every star and galaxy according to wavelength, allowing astronomers to determine what each object is made of and, in turn, how far it is from Earth.

The image on the left shows the full NISP field of view, with the zoom-in on the right (4% of NISP’s full field of view) demonstrating the extraordinary level of detail that NISP is already achieving. We see spiral and elliptical galaxies, nearby and distant stars, star clusters, and much more. The area of sky that it covers is only about a quarter of the width and height of the full Moon. (Image credit: ESA)

The researchers also tested Euclid's VISible instrument (VIS), to capture the cosmos in visible light (the same type of light that we can see with our unaided eyes). This dense starscape took Euclid 566 seconds to collect, according to ESA. Both test images are largely unprocessed, and only offer a hint at what Euclid will be capable of delivering when fully operational.

A black and white satellite iage of the infinite cosmos

Euclid’s VISible instrument (VIS) will image the sky in visible light (550–900 nm) to take sharp images of billions of galaxies and measure their shapes. This image was taken during commissioning of Euclid to check that the focused VIS instrument worked as expected. (Image credit: ESA)

What will Euclid study?

Once Euclid's data has been collected, scientists will use it to create two maps of the universe. The first will detail the spread of dark matter across our universe by gravitational lensing, in which matter bends light from a distant source through curved paths in space-time, thus magnifying it.

The second will use so-called baryon acoustic oscillations, gigantic matter shock waves created when the universe was hot and now frozen in time, as cosmic tree rings to study the universe's accelerating growth and its suspected cause: dark energy.

What is dark matter?

Dark matter is a mysterious and somewhat contradictory type of matter. It makes up an overwhelming 85% of the universe's matter; yet, because it doesn't directly interact with light, it is completely invisible.

So how do we know dark matter is there? While dark matter itself is invisible, the gravitational interactions it has with its surroundings are not — making its presence apparent in its extreme gravitational warping of galaxies, or in how it accelerates stars to otherwise inexplicable speeds as they orbit galactic centers.

The composition of dark matter isn't known. Some theories suggest that hypothetical particles called weakly interacting massive particles (WIMPs), each weighing 10 to 100 times the mass of a proton, could be ideal candidates to fill the theoretical gaps. Others have proposed that a minuscule particle less than a billionth the size of an electron — called an axion — could be the substance's primary candidate.

An example of gravitational lensing, whereby a foreground galaxy warps the light of a background one like a giant lens. (Image credit: ESA/Hubble & NASA, S. Jha Acknowledgement: L. Shatz)

What is dark energy?

Aside from a similar name, dark energy has little to do with dark matter. Dark energy is the name given to the enigmatic phenomenon of the universe's accelerating, runaway expansion — something that shouldn't be happening given the quantity of our universe's matter and the subsequent strength of its gravity. The answer cosmologists have offered is that some mysterious force in the fabric of the universe must be pushing everything outward.

NASA has estimated that 68% of the universe is composed of dark energy; 27% is dark matter, and visible matter makes up just 5%.

Editor's note: This article was updated on July 31st to include Euclid's first two test images.

Ben Turner
Staff Writer

Ben Turner is a U.K. based staff writer at Live Science. He covers physics and astronomy, among other topics like tech and climate change. He graduated from University College London with a degree in particle physics before training as a journalist. When he's not writing, Ben enjoys reading literature, playing the guitar and embarrassing himself with chess.

  • Giovani
    admin said:
    The Euclid space telescope will use its incredibly wide field of view to hunt for two of the universe's most mysterious components: dark matter and dark energy.

    Euclid space telescope launches this week. Here's what the groundbreaking mission will do. : Read more
  • Giovani
    Two forces making up 95 percent of creation. At the very least the reality we know is not viable. We are outside of the theories involving everything. We can detect the vast discrepancy in our technological margin, just enough to realize everything is not what we thought it to be.
    All the discussions of reality and philosophical interests are moot. What we have detected is reality, and humans are a mystery.
  • Hartmann352
    Euclid 'dark universe' telescope reveals its 1st sparkling images of the cosmos (photos)By Monisha Ravisetti

    July 31, 2023

    Scientists prepare Euclid in France before it is taken to its launch site. Photograph: Manuel Pédoussaut/ESA - M. Pédoussaut
    Artist's impression of the Euclid Space Telescope against the background of a nebula.
    Image credit: ESA/ATG medialab (spacecreft); NASA, ESA, CXC, C. Ma, H. Ebeling and E. Barrett (University of Hawaii/IfA), et .al and STScI (background).

    Two images taken by Euclid's instruments. The left was taken by VIS and the right by NISP.© ESA/Euclid/Euclid Consortium/NASA
    On Monday (July 31), the European Space Agency's Euclid telescope sent its first images back to Earth. And while these seminal portraits are certainly mesmerizing, they also confirm that the space observatory's instruments are working in tip-top shape.

    Euclid's success so far is really exciting because, to put it simply, this machine's purpose is to map outthe dark side of our universe by analyzing billions of galaxies that reside up to about 10 billion light-years away. Better yet, the agency also says this ambitious map will be in "3D," because it'll include the element of time to show how those realms evolved in tandem with a maturing cosmos.

    "The outstanding first images obtained using Euclid's visible and near-infrared instruments open a new era to observational cosmology and statistical astronomy," Yannick Mellier, astronomer at the Institut d'Astrophysique de Paris and Euclid Consortium lead, said in a statement. "They mark the beginning of the quest for the very nature of dark energy."

    Euclid launched on July 1 from Cape Canaveral in Florida. Now floating about a million miles (1.6 million km) from Earth, it joined the James Webb Space Telescope on July 28 at what's known as the second Lagrange point. Over the next few months, scientists will continue testing the machine until it starts officially developing its epic cosmic survey.

    The images you see above were taken with an instrument on Euclid called VIS, which stands for "Visible Instrument." As its name suggests, VIS captures the universe through the part of the electromagnetic spectrum that's visible to human eyes, wavelengths between 550 and 900 nanometers.

    On the left, you can see VIS' full field of view — and on the right, a zoomed-in version. ESA likens the range of the close-up to about one quarter the width and height of the full moon as seen from Earth.

    Some highlights of VIS' portraits include cosmic rays shooting straight across the field, a wealth of unmissable glittering stars, and most importantly, a few fuzzy blobs. Those blobs, ESA explains, are galaxies Euclid will investigate further while developing a highly detailed map of our universe, dark energy and all.

    "Ground-based tests do not give you images of galaxies or stellar clusters, but here they all are in this one field," Reiko Nakajima, VIS instrument scientist, said in the statement. "It is beautiful to look at, and a joy to do so with the people we've worked together with for so long."

    Next, we get to NISP, which stands for Euclid's Near-Infrared Spectrometer and Photometer. As ESA puts it, NISP has two roles. First, it can image galaxies in infrared light, or light invisible to human eyes that falls between about 950 and 2020 nanometers on the electromagnetic spectrum. The James Webb Space Telescope also taps into such infrared wavelengths, which is why scientists often say it's unveiling an invisible universe. It quite literally is.

    Second, NISP can measure precisely how much light each galaxy emits — this latter bit can tell us how far away those galaxies are.

    The NISP images you see above are pretty similar to the VIS set in that the left side includes NISP's full field while the right shows a zoomed-in section.

    But before reaching the NISP detector, deep space light captured by Euclid also passes through some cool filters. And that offers some pretty awesome results. These filters can do things like measure brightness at a specific infrared wavelength, which helps with NISP's galactic distance measurements.

    "Although these first test images are not yet usable for scientific purposes, I am pleased that the telescope and the two instruments are now working superbly in space," Knud Jahnke, from the Max Planck Institute for Astronomy (MPIA) in Heidelberg who works on Euclid's NISP instrument, said in a statement.

    And in fact, one of these filters is why NISP offered us a third test image.

    Besides looking like an early 2000's computer screensaver, this image is important because each streak represents an individual light spectrum of a galaxy or star. Euclid has a device known as a "grism" that can basically split cosmic light into a full spectrum of wavelengths before sending the data to NISP.

    With this process, scientists can determine how far away a certain galaxy is, for instance, as well as what the galaxy is chemically made of.

    "We've seen simulated images, we've seen laboratory test images," William Gillard, NISP instrument scientist, said in the statement. "It's still hard for me to grasp these images are now the real universe. So detailed, just amazing."

    Now, if you've still been stuck on the fact Euclid can help us understand the dark universe, here's what that means.
    What's next for Euclid?Dark energy and its partner-in-crime, dark matter, constitute some of the biggest and most fascinating questions to exist in astronomy today. Neither phenomena can be seen by human eyes, yet still appear to be holding our universe together.

    For starters, space is constantly expanding outward in every direction like an unpoppable balloon. But the weird thing is, this ballooning seems to be happening at speeds scientists can't quite account for with all the visible stuff in our universe. Thus, something else must be acting to accelerate the cosmic expansion. Scientists call that "something" dark energy.

    Meanwhile, within the expanding universe, there seems to be some sort of glue making sure galaxies are held in place and dictating the way they're arranged. For example, scientists calculate that intergalactic gas and stars often move around as though there's extra gravity pulling on them. Presumably, this is because some sort of invisible material surrounds the galaxies these objects live in (perhaps like a halo) and therefore exerts gravitational forces on them. That unseeable "glue" is known as dark matter.

    Dark matter and dark energy aren't necessarily made up of one, or even two, things. They could be made up of a bunch of different components. Scientists just use these as bulk terms to describe gaps in our understanding.

    All we know for sure, right now, is that the dark universe exists.

    But if Euclid's mission of exquisitely mapping the universe over the next six years or so pans out, perhaps scientists will gain some clues as to what the dark universe truly is.

    This is because, as dark matter and energy interact with things in space, laying out the distribution and evolution of those things can tell us where the dark universe fits into the story.

    "I have full confidence that the team behind the mission will succeed in using Euclid to reveal so much about the 95% of the universe that we currently know so little about," ESA director, General Josef Aschbacher, said in the statement.

    "After more than 11 years of designing and developing Euclid, it's exhilarating and enormously emotional to see these first images," Euclid project manager, Giuseppe Racca, said in the statement. "It's even more incredible when we think that we see just a few galaxies here, produced with minimum system tuning. The fully calibrated Euclid will ultimately observe billions of galaxies to create the biggest-ever 3D map of the sky."

    Euclid and the James Webb Space Telescope have two key features in common. Both operate in the near-infrared, at wavelengths predominantly too long for the human eye, and both will be located at Lagrange point 2. However, where the JWST has the capacity to peer back almost to the dawn of time or measure the atmospheres of planets around other stars. Euclid cannot go so deep.

    Instead, Euclid’s strength lies in its wide field, 2.5 times times as large as the full Moon. In this way it will study some 1.5 billion galaxies across all the sky not obscured by the Milky Way or zodiacal light. It is hoped that what it learns about their shape and distribution will distinguish between competing models of the evolution of the cosmos.

    “Where Webb can observe extremely far back in time and zoom into the details, Euclid can go fast and wide,” the European Space Agency (ESA) writes. “In a single observation Euclid can record the data from an area of the sky more than one hundred times bigger than that imaged by Webb’s camera, NIRCam.”

    If it fulfils even one of these it will be a raging success. More likely, it will take us a few steps along the road to each of them, and hopefully point the way by which other instruments can take things further. In the short term, that will predominantly be the JWST. quotes Euclid project scientist René Laureijs as saying, "It would be beautiful if the two telescopes are online and James Webb could follow up the new findings of Euclid."

    Euclid’s mirror is smaller than Hubble’s, let alone the JWST, so its resolution will be similarly limited. Lacking the capacity to see the universe in great detail, Euclid should find things of interest that require further exploration. In some cases this may be possible from Earth using telescopes that operate in visible light or radio waves. Often, however, we will need something that can see further but at the same frequencies as Euclid, and while the forthcoming telescope can see wavelengths as short as green light, for most of its spectrum that means the JWST.

    For example, one of Euclid’s tasks is to study the way light from distant galaxies is affected by passing through the gravitational fields of closer ones. If any of these stand out as particularly unusual or significant, higher-resolution studies may be required.

    One problem is that the JWST is already a year into its anticipated five-year mission. While over-performance during launch means it may have the fuel to go a little longer, it won’t last forever. Euclid, with an anticipated 6-year mission, will probably outlast it, and will have to count on the Nancy Grace Roman Space Telescope launching much closer to its intended date than the JWST did.

    Euclid was intended to be launched last year on a Russian Soyuz rocket. However, after the invasion of Ukraine, the European Space Agency ended its cooperation with the Russian space agency, Roscosmos, and instead signed a deal to use a Falcon 9 rocket from Elon Musk's SpaceX company. The €1bn (£850m) Euclid mission will investigate the universe’s two most baffling components: dark energy and dark matter. The former is the name given to a mysterious force that was shown – in 1998 – to be accelerating the expansion of the universe, while the latter is a form of matter thought to pervade the cosmos, provide the universe with 80% of its mass, and act as a cosmic glue that holds galaxies together. Both dark energy and dark matter are invisible and astronomers have only been able to infer their existence by measuring their influence on the behaviour of stars and galaxies.