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Euclid is an ESA medium class astronomy and astrophysics space mission. Euclid was selected by ESA in October 2011 (see the Euclid ESA page). Its launch is planned for 2023. In June 2012 ESA officially selected the “Euclid Consortium” as the single team having the scientific responsibility of the mission, the data production and of the scientific instruments.

The Euclid mission aims at understanding why the expansion of the Universe is accelerating and what is the nature of the source responsible for this acceleration which physicists refer to as dark energy. Dark energy represents around 75% of the energy content of the Universe today, and together with dark matter it dominates the Universes’ matter-energy content. Both are mysterious and of unknown nature but control the past, present and future evolution of Universe.

Euclid will explore how the Universe evolved over the past 10 billion years to address questions related to fundamental physics and cosmology on the nature and properties of dark energy, dark matter and gravity. Euclid will also provide insightful information on the physics of the early universe and on the initial conditions which seed the formation of cosmic structure.

The imprints of dark energy and gravity will be tracked by using two complementary cosmological probes to capture signatures of the expansion rate of the Universe and the growth of cosmic structures: Weak gravitational Lensing and Galaxy Clustering (Baryonic Acoustic Oscillations and Redshift Space Distortion).

To accomplish the Euclid mission ESA has selected Thales Alenia Space (see also the ESA press release ) for the construction of the satellite and its Service Module and Airbus (Defence and Space) for the Payload Module.

Euclid will be equipped with a 1.2 m diameter Silicon Carbide (SiC) mirror telescope made by Airbus (Defence and Space) feeding 2 instruments, VIS and NISP, built by the Euclid Consortium : a high quality panoramic visible imager (VIS), a near infrared 3-filter (Y, J and H) photometer (NISP-P) and a slitless spectrograph (NISP-S). With these instruments physicists will probe the expansion history of the Universe and the evolution of cosmic structures by measuring the modification of shapes of galaxies induced by gravitational lensing effects of dark matter and the 3-dimension distribution of structures from spectroscopic red­shifts of galaxies and clusters of galaxies.

The satellite will be launched by a Falcon9 rocket of SpaceX Corp. and after a 30 days transit will orbit around the L2 Sun-Earth Lagrangian point for a 6 years mission.

Euclid will observe 15,000 deg2 of the darkest sky that is free of contamination by light from our Galaxy and our Solar System (see the ESA Euclid mission summary ). Three “Euclid Deep Fields” covering around 40 deg2 in total will be also observed extending the scientific scope of the mission the high-redshift universe.

The complete survey represents hundreds of thousands images and several tens of Petabytes of data. About 10 billion sources will be observed by Euclid out of which more than 1 billion will be used for weak lensing and several tens of million galaxy redshifts will be also measured and used for galaxy clustering. The scientific analysis and interpretation of these data is led by the scientists of the Euclid Consortium.

An artist view of the Euclid Satellite – © ESA