Euclid’s 1.7-million-GB release spans more than 900 million galaxies

By Rebecca Stone

The European Space Agency (ESA) has released 1.7 million GB of data from its €1.4bn Euclid mission, capturing light from more than one billion objects in its first major batch.

The package, called DR1-Foundation, is the mission’s first major data release and spans around 13 months of observations and 1,900 square degrees of sky. ESA compares that coverage with 9,500 full Moons.

The release contains:

• More than 900 million galaxies.
• More than 60 million quasar candidates, which ESA says will improve understanding of the first generation of galaxies.
• 15,000 strong gravitational lens candidates (foreground galaxies that significantly distort light from distant galaxies), which ESA says can shed light on dark matter.

ESA director of science Carole Mundell said: “This major Euclid data release represents the largest space-based survey of its kind, laying the foundation of future discovery in a new regime for astronomy and demonstrating the excellence of European technology, science and international collaboration.”

That characterization establishes an ESA scale claim, not a completeness guarantee. The announcement gives no catalogue-purity rate, positional-error budget or confirmation threshold for the quasar or lensing candidates. Those measures will determine how reliably the counts can support population-level research.

Euclid project scientist Valeria Pettorino said: “We’re now releasing more than a year of data covering a significantly larger area. This unlocks ground-breaking science.”

For research managers, the 1.7-million-GB volume turns storage, data transfer and catalogue processing into standing budget items. It also gives teams a working dataset for testing analysis pipelines before the survey reaches its announced full release.

Euclid now operates at Lagrange Point 2, the gravitational balance point about 1.5 million kilometres beyond Earth’s orbit around the Sun.

What does the observing hardware contribute?

Euclid uses a 1.2-metre-diameter telescope, a camera and a spectrometer (an instrument for measuring light by wavelength) to plot a three-dimensional map of the galaxy distribution. ESA states that its images are about four times as sharp as those from current ground-based telescopes, although the announcement provides no baseline resolution or matching protocol.

That hardware supports a multi-stage analysis product rather than an image-only survey. For portfolio planning, the work extends from observation to image processing, spectral analysis, catalogue storage and quality control. The announcement gives no per-instrument sensitivity or catalogue completeness, so teams cannot assume uniform measurement quality across every released candidate.

How much of the survey remains?

The operational sequence provides the context for the current release:

• July 2023: Euclid launched.
• November 2023: The mission released its first images.
• February 2024: Routine observations began.
• May 2024: Euclid released its first science results.
• 2025: The first preliminary survey-data batch, comprising a few days of observations over around 60 square degrees, became available.

ESA reports that the released survey data covers about 14% of the sky area Euclid will survey. The announced first full data release is set for mid-2027, making the current package a staged delivery rather than the completed survey.

For planning purposes, mid-2027 is a schedule projection, not a measured completion date. The announcement provides no further release dates beyond the 2025 preliminary batch, so research programmes cannot treat the present catalogue as a fixed endpoint.

Who operates Euclid?

The Euclid Consortium comprises around 2,600 members from more than 15 countries. For portfolio planning, that international membership turns data stewardship, shared computing and follow-up analysis into recurring resource requirements alongside the €1.4bn observing programme.

For laboratories and observatories planning their next analysis cycle, the immediate task is to convert candidate lists into validated samples. The announcement provides scale but no catalogue-purity rate, positional-accuracy measurement or error budget for the three-dimensional map. Those limits will determine whether the galaxy, quasar and lensing counts can support conclusions about population properties.

The next decisive checkpoint is the mid-2027 full release, which will test whether catalogue scale and quality can be sustained across the remaining survey.