Euclid telescope delivers first major data release toward a 3D map of the universe

The European Space Agency's Euclid spacecraft has released the first large batch of data from its survey of the "dark universe," a catalogue covering more than 900 million galaxies and 60 million candidate quasars across roughly a tenth of the sky. The release, called DR1-Foundation, is the raw material for what ESA describes as the best three-dimensional map of the cosmos ever attempted, and it marks the moment the six-year mission shifts from taking pictures to doing large-scale cosmology.

Euclid launched from Cape Canaveral in July 2023 and has spent roughly 13 months of its planned six-year survey gathering the observations behind this release, according to the European Space Agency. The spacecraft operates from the Sun-Earth L2 Lagrange point, about 1.5 million kilometers from Earth, imaging in visible and near-infrared light with a field of view wide enough to capture more than 100 times as much sky in a single exposure as the Hubble or James Webb space telescopes, according to Leiden University, whose astronomers helped build the mission's theoretical and statistical tools.

A billion-object catalogue

The new release covers about 1,900 square degrees of sky, an area equivalent to roughly 9,500 full moons, drawn mostly from Euclid's Wide Survey. ESA says the dataset includes more than a billion individually catalogued objects, over 900 million galaxies, more than 60 million quasar candidates, spectra for upward of 160 million sources, and about 15,000 candidate strong gravitational lenses, instances in which the gravity of a foreground galaxy or cluster bends and magnifies the light of something far more distant behind it. The underlying imagery, Leiden University notes, totals around 2.5 trillion pixels and 1.7 million gigabytes, and corresponds to roughly 14 percent of the total sky area Euclid is expected to survey by the time its mission ends.

By comparison, Euclid's first "quick" data release in March 2025 covered only about 63 square degrees, a few days' worth of observations concentrated on three deep fields. The new release is a different order of magnitude: a full year-plus of wide-area survey data, now open to the global research community through ESA's science archive.

Testing dark matter, dark energy and gravity itself

Euclid exists to attack one of cosmology's oldest open problems: ordinary matter accounts for only about 5 percent of the universe's contents, with dark matter making up roughly 27 percent and dark energy, the mysterious force accelerating cosmic expansion, the remaining 68 percent. Rather than detecting dark matter or dark energy directly, Euclid maps how galaxies are distributed in space and how their shapes are subtly warped by gravitational lensing, then uses statistical patterns across hundreds of millions of galaxies to constrain competing theories.

"We can describe the history of the universe remarkably well," said Alessandra Silvestri, a Leiden University professor and lead of the Euclid Consortium's theory working group, in comments released by the university. She said the open question is "whether our current understanding of gravity is complete, or not," and that answering it requires statistics rather than individual objects: "A single galaxy cannot tell us much about dark energy or the laws of gravity. But billions of galaxies can." Her Leiden colleague Koen Kuijken, describing Euclid's wide-field design, said the telescope "sees more than a hundred times as much of the sky in one image" as Hubble or Webb, and that over its six-year mission it will map roughly a third of the entire sky.

The release builds on results Euclid has already produced from smaller samples of its data. In July, mission scientists reported that Euclid had identified 31 quasars from the universe's first billion years, including two dating to when the cosmos was about 670 million years old, among the most distant such objects known, according to a press release from Imperial College London. Each is powered by a supermassive black hole roughly a billion times the mass of the sun. Imperial physicist Daniel Mortlock, who has co-led Euclid's quasar search since 2014, called the find the payoff of a long "needle in a haystack" effort.

A resource for the wider astronomical community

Because Euclid's archive is public, the practical significance of this release extends well beyond the roughly 2,000 scientists formally affiliated with the Euclid Consortium. Researchers studying galaxy evolution, supermassive black holes, star clusters and the structure of the Milky Way's own neighborhood can now mine a dataset an order of magnitude larger than anything comparable that has come before, without having to wait for the mission's full cosmological analysis. ESA has already highlighted individual objects captured in the release, including close-up views of the spiral galaxy Messier 81, the ring galaxy NGC 1291 and the galaxy cluster Abell 3128, alongside the newly compiled catalogue of strong gravitational lenses.

Handling that volume of data was itself a technical undertaking. "Storing and sharing such large catalogues, with more than a billion objects, was no mean feat," said Bruno Altieri, an ESA archive scientist at the European Space Astronomy Centre near Madrid, in the agency's statement. Natalie Lines, a Euclid Consortium scientist at the University of Portsmouth, said the lens catalogue bears out predictions made years before launch: "Over 10 years ago, we forecast that Euclid would revolutionize the field of strong lens discovery." Barbara Sartoris, of the Côte d'Azur Observatory's Lagrange Laboratory, said the release offers "an unprecedented view of large samples of ancient galaxy clusters," the gravitationally bound structures cosmologists use to trace how matter has clumped together over billions of years.

"These are far more than beautiful pictures; today marks a scientific milestone in our study of the cosmos," said Carole Mundell, ESA's director of science, in the agency's announcement of the release.

What comes next

DR1-Foundation is explicitly a staging post. ESA split Euclid's first full data release into two parts earlier this year specifically to get raw data, calibrated images and spectra into researchers' hands as early as possible, while the more processed, higher-level products needed for precision measurements of galaxy clustering and weak lensing continue to be validated. According to the mission's published timeline, that fuller version, DR1 proper, is due in June 2027, when the Euclid Consortium also expects to publish its first results testing whether the standard model of gravity holds up at the largest cosmic scales, the central question the mission was built to answer.

Euclid's wide survey remains well short of its endpoint. The roughly 1,900 square degrees released this week will eventually grow to cover about a third of the entire sky, some 14,000 square degrees, as the spacecraft continues its planned run through the late 2020s. Each additional year of observing adds to the statistical power scientists can bring to bear on dark energy, and each new catalogue, mission scientists say, will be released to the public on a similar rolling basis rather than held back for a single, final announcement.