A space telescope for the study of the Dark Universe
Recent measurements of the inhomogeneities of the Cosmic Microwave Background (CMB), the expansion of type Ia supernovae (SNIa), and the large-scale structure of the Universe converge toward a new cosmological model known as the “ΛCDM model.” Paradoxically, this model relies on three components whose origin and nature remain unknown: dark matter (CDM for Cold Dark Matter), dark energy (Λ), and the fields responsible for inflation. Identifying and understanding these three ingredients is the current challenge of cosmology and the likely source of a revolution in fundamental physics.
To uncover these “dark” components, which make up more than 95% of the content of the Universe, the Euclid satellite was developed to observe the effects of gravitational distortions that provide a direct measurement of the distribution of dark matter in the Universe. It precisely measures the weak distortions of distant galaxy images caused by the gravitational influence of large-scale structures along the line of sight. Studying these distortions can also be used to measure cosmological parameters and, in particular, the behavior of “dark energy,” which affects the growth of cosmic structures.
Euclid’s wide-field space imaging avoids the disturbing effects of Earth’s atmosphere, which currently limit ground-based telescope surveys. It will deliver very high sensitivity (more accurate galaxy images) and, thanks to sharp and stable images, reduce systematic optical errors that are critical for studying weak distortions.
After several years of preliminary studies in competition with other missions, Euclid was selected by ESA in October 2011 and officially adopted in June 2012.
CEA teams initiated this mission and are deeply involved, occupying key positions in its management, instrument development, ground segment, and science activities. Euclid is a medium-class (M-class) mission of ESA’s Cosmic Vision program (2015–2025). Its main objective is to study the origin of the accelerated expansion of the Universe using two distinct cosmological probes: weak gravitational lensing and the distribution of galaxies in space (galaxy clustering).
The Euclid satellite’s payload consists of a 1.2 m telescope equipped with two instruments:
- a wide-field imager for visible wavelengths (VIS),
- a near-infrared spectro-imager (NISP).
The satellite will be placed at the Lagrange point L2 for a 6-year mission to observe the entire extragalactic sky.
CEA’s involvement in Euclid
Irfu played a key role in the mission’s selection by coordinating the scientific consortium that, as early as 2004, proposed a mission to study the dark Universe in response to ESA’s Cosmic Vision call for themes. In 2007, we initiated the DUNE (Dark UNiverse Explorer) mission proposal, and from September 2008 to September 2009, we coordinated both the scientific and technical preparatory studies for the instruments of the Euclid mission, which resulted from the merger of the DUNE and SPACE proposals. In October 2010, we established and led the Euclid scientific consortium in response to ESA’s call for proposals for the delivery of Euclid’s entire payload and associated scientific ground segment.
Since then, we have held key positions in the Euclid project: we are deeply involved at the highest levels in the management of the Euclid Consortium (management coordination, global system responsibility for the mission, scientific responsibility for the ground segment), in instrument development activities (in charge of supplying key components for both instruments), and in the preparation of the scientific ground segment.
For the VIS instrument, Irfu supplied the focal plane (built around 36 CCDs totaling more than 500 million pixels) and a motor and power control system, as well as the cryo-mechanisms that will position the NISP filters at low temperature with great precision and extreme reliability.
The scientific ground segment is a crucial part of Euclid: more than one billion galaxies will be measured for weak lensing analysis. We are involved at every stage of the data processing associated with weak lensing studies: we contribute to the development of image simulations from the VIS instrument, to competitive studies of galaxy shape measurement data processing, and to the development of algorithms for the production of high-level scientific outputs, thereby leveraging our expertise in statistical data processing methods and their application to cosmology.
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