The universe just got a whole lot clearer—thanks to the Euclid space telescope, which in just one week captured 26 million galaxies in its first deep-field images. This stunning accomplishment marks a bold beginning in Euclid’s ambitious six-year mission to map the dark universe, a term that encompasses the elusive forces of dark matter and dark energy.
Unveiling the Mission’s Purpose
The primary mission of Euclid is to understand the invisible. Specifically, it aims to decode dark energy, the mysterious force that is causing galaxies to drift apart faster and faster. Unlike the galaxies, stars, and planets we can see, dark energy makes up about 70% of the universe—yet we know almost nothing about it.
Euclid will do this by creating the most precise 3D map of the universe ever constructed. By observing how billions of galaxies have moved and evolved over cosmic time, scientists can trace how dark energy has shaped the structure and expansion of the universe.
26 Million Galaxies—and That’s Just the Start
In March 2025, ESA released the first official preview of Euclid’s data, and the results were jaw-dropping: 26 million galaxies observed in just one week of scanning Euclid’s Deep Field South. Some of these galaxies are over 10.5 billion light-years away, meaning Euclid is giving us a look at galaxies as they were when the universe was just a few billion years old.
This preview represents only a fraction of what Euclid will accomplish. Over the course of its six-year primary mission, Euclid is expected to observe more than 1.5 billion galaxies, helping us build a complete timeline of how cosmic structures like galaxies and galaxy clusters formed—and more importantly, how they moved under the influence of dark energy.
Seeing the Invisible: Gravitational Lensing and Dark Matter
To track the distribution of dark matter, Euclid doesn’t need to see it directly. Instead, it measures the gravitational lensing effect. When light from distant galaxies travels through space, it is bent by the gravity of both visible and invisible mass. This bending subtly distorts the shape of the galaxies we observe, like looking through a warped glass window.
Even though this effect is extremely subtle, analyzing billions of galaxies allows Euclid to spot these distortions and map the presence of dark matter—which, along with dark energy, dominates the structure of the universe.
Deep Fields: Patience Pays Off in Astronomy
Euclid’s success hinges on its strategy of long, focused observations in areas called deep fields. These are parts of the sky where Euclid will repeatedly return over time, collecting more and more light—similar to keeping a camera shutter open longer to capture a dim scene.
In the case of Deep Field South, Euclid will observe this area for about 40 weeks over its mission duration. This extended exposure lets scientists see fainter and more distant galaxies, some of which are beyond the reach of earlier telescopes like Hubble.
While Hubble revealed the surprising richness of galaxies in its deep field images in 1995, Euclid builds on that legacy with far greater field-of-view and depth, making it a powerful new tool for cosmic exploration.
Cosmic Cartography: Mapping the Expansion of the Universe
Understanding how fast the universe is expanding—and how that rate has changed—is the central aim of Euclid’s science mission. By mapping galaxies at different distances, scientists can essentially rewind the clock of the universe. Light from faraway galaxies takes time to reach us, so looking farther out also means looking further back in time.
With these observations, Euclid will create detailed 3D maps that show not just where galaxies are, but when they were in the history of the universe. This time-lapse view will allow researchers to track the growth of structures and see how dark energy has influenced their motion over billions of years.
Global Collaboration Behind the Mission
Euclid is the result of a massive international collaboration. The ESA leads the mission, but NASA plays a crucial role through its contribution of hardware, electronics, and scientific expertise. The Near Infrared Spectrometer and Photometer (NISP) instrument was built with significant NASA input, including sensor-chip electronics designed and tested at NASA’s Jet Propulsion Laboratory (JPL) and Goddard Space Flight Center.
The Euclid Consortium, a collaboration of more than 2,000 scientists across 300 institutes in 15+ countries, is responsible for analyzing the data and developing the mission’s scientific tools. This vast network ensures the data will be explored from every angle possible.
The Big Picture: What This Means for Cosmology
Euclid’s early success is not just about counting galaxies—it’s about using those galaxies as markers in the universe’s evolution. With each observed cluster or distorted shape, Euclid provides a puzzle piece in understanding what dark energy is, how it behaves, and whether our models of the universe need an upgrade.
Will dark energy turn out to be Einstein’s cosmological constant? Or could it be something else entirely—something dynamic that changes over time? The answers lie in the data Euclid is collecting right now.
What Comes Next: Looking Toward 2026 and Beyond
While these early images are exciting, the best is yet to come. The first full cosmology dataset from Euclid will be released in October 2026, containing much more precise information from ongoing observations.
Euclid will also work hand-in-hand with NASA’s Nancy Grace Roman Space Telescope, launching by 2027, which will also focus on dark energy. Together, these two missions will provide a panoramic, detailed, time-stamped map of the universe—offering humanity the best chance yet to understand its origins, its makeup, and its fate.
Conclusion: Euclid is Just Getting Started
Euclid’s ability to spot 26 million galaxies in just one week shows that we’ve entered a new era of cosmic exploration. With the tools to see both deep into space and far into the past, we are finally beginning to understand how the universe came to be—and where it’s headed.
