On March 19, 2025, the European Space Agency's groundbreaking Euclid mission unveiled its first vital survey data, a monumental step in humanity's quest to understand the universe. This initial release showcases stunning images of hundreds of thousands of galaxies in diverse shapes and sizes, highlighting their intricate large-scale structure within the cosmic web.

Spanning a vast region of the sky represented in three expansive mosaics, the data also reveals numerous galaxy clusters, active galactic nuclei, and transient celestial events. Notably, it features the first classification survey of over 380,000 galaxies and 500 gravitational lens candidates, achieved through a collaborative effort between artificial intelligence and citizen scientists.

"Euclid is proving to be humanity's ultimate discovery machine," commented Prof. Carole Mundell, ESA's Director of Science. "By surveying galaxies on an unprecedented scale, we are unlocking a treasure trove of information that addresses some of modern science's most pressing questions and promises to facilitate scientific progress for generations to come."

Delving into Euclid's Deep Fields

The Euclid mission is planned to explore three specific areas of the sky, ultimately delivering astonishingly deep cosmic observations. In its first week alone, Euclid identified an astonishing 26 million galaxies, many of which are located up to 10.5 billion light-years away.

As the mission progresses, Euclid will revisit these areas multiple times—between 30 to 52 times over its six-year duration—enhancing the detail of the observed data with each scan. The first glimpse provided covers 63 square degrees, an area more than 300 times the size of the full moon, giving a taste of the grand cosmic atlas Euclid aims to complete, which will encompass one-third of the entire sky, or 14,000 square degrees.

"It's remarkable that just one observation has yielded such a wealth of information for various astronomical applications, from galaxy morphology to clusters and star formation," shared Valeria Pettorino, ESA's project scientist for Euclid.

As the mission unfolds, Euclid will focus on accurately measuring the diverse shapes and distribution of billions of galaxies using its high-resolution visible imaging instrument (VIS) and the near-infrared instrument (NISP) to decipher distances and masses.

The initial data already hints at the grand organization of galaxies within the cosmic web, composed of both ordinary and dark matter, essential to unraveling the mysteries surrounding dark energy and dark matter, which constitute roughly 95% of the universe.

AI and Citizen Science Driving Discovery

Throughout its six-year journey, Euclid is set to capture images of more than 1.5 billion galaxies and transmit around 100 GB of data daily. The massive dataset poses substantial challenges in searching, analyzing, and cataloging galaxies. However, advancements in AI, combined with the enthusiastic contributions of thousands of citizen scientists, are integral to the mission's success.

"AI is pivotal in maximizing Euclid's vast dataset, allowing us to deliver cutting-edge scientific findings in weeks instead of years," explained Mike Walmsley, an expert in astronomical deep learning algorithms at the University of Toronto.

A landmark achievement is the release of the first comprehensive catalog of over 380,000 galaxies, meticulously classified according to unique morphological features. This effort was propelled by a campaign on the Galaxy Zoo platform, during which nearly 10,000 volunteers helped train the AI algorithm dubbed "Zoobot" to recognized galaxy features.

The initial catalog represents a fraction of the total galaxies expected to be imaged, with future releases projected to encompass detailed observations of an order of magnitude more galaxies than ever seen before. These insights will aid in unraveling enigmatic questions regarding the formation of spiral arms and the growth of supermassive black holes.

Gravitational Lensing: Peering into Dark Matter

Euclid employs gravitational lensing as one of its key techniques to investigate dark matter distribution in the universe. This phenomenon, where light from distant galaxies is bent by foreground matter, can result in astounding features like Einstein rings and arcs.

With AI's initial analysis complemented by citizen science and expert reviews, Euclid's first catalog has identified 500 galaxy-galaxy strong lens candidates, nearly all previously unknown. As the mission proceeds, Euclid aims to document roughly 100,000 galaxy-galaxy strong lenses, amplifying our current understanding by nearly 100 times.

Additionally, Euclid will measure "weak" lensing, allowing for subtler distortions to be detected through statistical analysis of numerous galaxies. This will enable a three-dimensional view of dark matter distribution over the past 10 billion years of cosmic history.

"Thanks to Euclid’s unparalleled capabilities, we are accelerating the pace of discovery and uncovering vast regions of the sky like never before," stated Pierre Ferruit, ESA's Euclid mission manager.

As we stand on the brink of a new era in cosmic exploration, the first data release from Euclid heralds an exciting future filled with possibilities, paving the way for groundbreaking revelations about the universe and its profound mysteries.