Euclid is an ESA medium class mission selected for launch in 2019 in the Cosmic Vision 2015-2025 programme (ESA PR selection ). The main goal of Euclid is to understand the origin of the accelerating expansion of the Universe. To achieve this, it is proposed to build a satellite equipped with a 1.2 m telescope and three imaging and spectroscopic instruments working in the visible and near-infrared wavelength domains. These instruments will explore the expansion history of the Universe and the evolution of cosmic structures with look back time by measuring shapes and redshifts of galaxies as well as the distribution of clusters of galaxies as function of redshift over a very large fraction of the sky. The satellite will be launched by a Soyuz ST-2.1B rocket and transferred to the L2 Lagrange point for a 6 years mission (see the ESA Euclid mission summary ).
Two concepts for EUCLID Satellite – © ESA
Euclid will address key fundamental cosmological questions. Is dark energy merely a cosmological constant, as first discussed by Einstein, or is it a new kind of field that evolves dynamically with the expansion of the universe? Alternatively, is dark energy instead a manifestation of a break-down of General Relativity and deviations from the law of gravity? What are the nature and properties of dark matter? What are the initial conditions which seed the formation of cosmic structure? The imprints of dark energy and gravity will be tracked by using two robust and complementary cosmological probes of the dark universe that are best suited to capture signatures of the expansion rate and the growth of cosmic structures in the Universe over the last 10 billion years, namely Weak gravitational Lensing and Galaxy Clustering (Baryonic Acoustic Oscillations and Redshift Space Distortion). These two probes will be complemented by independent information also derived from Euclid data on clusters of galaxies and the Integrated Sachs-Wolf effect.