Euclid Early Release Observations (ERO): Public data release May 2024 

The ERO programme is an initiative of ESA and the Euclid Science Team: it includes one day of observations, taken before the start of the nominal survey, to showcase the capabilities of the ESA Euclid mission. These observations are not part of the nominal survey, and address legacy science rather than Euclid core science. These are the first Euclid data released to the general community, starting 23rd May 2024. Here you can find the ESA press release of 23rd May 2024

Selected ERO Projects

In February 2023, a call for proposals was issued within the Euclid Science Collaboration (ESA, Euclid Consortium and the Independent Legacy Scientists). The objective was to identify Euclid observations with both communication/outreach and scientific merit. The ERO programme committee selected 6 proposals, covering observations including a variety of objects at different distances and scales in the Universe. The teams supporting these proposals carried out the data analyses.

The selected projects, their targets and lead scientists are:

  • The Fornax galaxy cluster seen with Euclid - Lead scientist: Ariane Lançon (Strasbourg Observatory).
  • Euclid view of Milky Way globular clusters - Lead scientist: Davide Massari (INAF-OAS Bologna).
  • A first glance at free-floating baby Jupiters with Euclid - Lead scientist: Eduardo Martín (Instituto de Astrofísica de Canarias).
  • A Glimpse into Euclid’s Universe through a giant magnifying lens - Lead scientist: Hakim Atek (Institut d’Astrophysique de Paris).
  • The Perseus cluster of galaxies - Lead scientist: Jean-Charles Cuillandre (CEA, AIM, Université Paris-Saclay).
  • A Euclid showcase of nearby galaxies - Lead Scientist: Leslie Hunt (INAF-AO Arcetri, Firenze).

Data Collection

The ERO proposals and initial observations were selected before Euclid launch assuming the pre-launch schedule for the commissioning and the start of the nominal survey. The actual schedule had to account for the update of the Fine Guidance Sensor (FGS) software update, causing the start of the Performance Verification Phase in which the EROs should have been collected, several weeks later than planned.

Before the re-start of the Performance Verification Phase, the operations teams managed to schedule a number of observations before they would move out of the visibility window of Euclid. A subset of these observations could be executed successfully without guiding errors, and are used as ERO showcases. However, the majority of the successful ERO observations have been collected during the Performance Verification Phase in the period from 29 September until 3 December 2023.

All 17 ERO fields are illustrated here.

Data Products

The imaging data have been processed using processing pipelines developed by J.-C. Cuillandre (CEA, AIM, Université Paris-Saclay). The detailed description of the ERO processing is described in this overview paper, which is part of the set of the ERO papers released in May 2024.

The ERO pipeline is designed from the ground up for diffuse emission science (low surface brightness Universe, LSB) and standard point/compact source science. It is a direct legacy from proven imaging pipelines developed for CCD and FPA mosaics at the CFHT over the past two decades with several steps relying on E. Bertin's AstrOmatic toolbox. It is fully independent from the processing functions developed by the Euclid Science Ground Segment, which are optimised for the generation of data products supporting the core cosmology and will be used for the nominal survey.

ERO Public DATA Release: 23 MAY 2024

These data are associated with all products released during the media briefing on 7 Nov 2023 and on 23 May 2024. The data include processed image stacks and validation catalogues of fields of all 6 selected ERO projects, in the VIS Euclid bands, for a total of 17 fields on the sky.

A total of 10 million unique sources were extracted from the VIS images.

How to access the images

ERO images are available on ESASky, where you can explore each of them in great detail: 

Abell 2390 

NGC 6744 



Abell 2764.

The ESA press release of 23rd May 2024 also contains direct links to all 5 full-view images. Within each image page the links to the related cutouts are also available.

How to access the data files

You are welcome to access, use and analyse Euclid ERO data. When doing so, please make sure you credit the work necessary to release these data by following these instructions. The links to the data can be found here:

How to access the ERO scientific papers

Scientific papers associated to the ERO Release in May 2024 are available here