Space Exploration
Euclid is a European Space Agency (ESA) space telescope launched on 1 July 2023 to investigate the nature of dark matter and dark energy by mapping the geometry of the Universe. It operates at the Sun–Earth L2 Lagrange point, where it performs a wide and deep survey of extragalactic sky, measuring the shapes and redshifts of billions of galaxies. Euclid's two instruments, VIS and NISP, work in tandem to produce high-precision images and spectra, enabling tests of general relativity on cosmic scales and probing the accelerated expansion of the Universe.
Euclid is a medium-class mission in ESA's Cosmic Vision programme, selected in 2011 and built by a consortium of European institutes with NASA contributions. Its primary goal is to map the large-scale structure of the Universe with unprecedented precision, using two complementary probes: weak gravitational lensing and baryon acoustic oscillations. The spacecraft carries a 1.2 m Korsch telescope feeding two instruments: the visible imager (VIS) and the near-infrared spectrometer and photometer (NISP). VIS provides high-resolution images of galaxies, while NISP measures their photometric and spectroscopic redshifts, allowing a 3D map of cosmic structure. The mission operates from a halo orbit around the Sun–Earth L2 point, providing a stable thermal environment and unobstructed view of the sky. Euclid's survey covers about 15,000 square degrees of the extragalactic sky, excluding the Milky Way plane and zodiacal light regions, and will observe over a billion galaxies out to redshift ~2.
Euclid aims to answer fundamental questions about the accelerated expansion of the Universe and the nature of dark energy. By measuring the distortion of galaxy shapes caused by weak gravitational lensing, it can map the distribution of dark matter and test whether general relativity holds on cosmic scales. Combined with baryon acoustic oscillation measurements from galaxy clustering, Euclid will constrain cosmological parameters such as the dark energy equation of state and the growth rate of structure. The mission also probes the neutrino mass sum and tests inflationary models through primordial non-Gaussianity. Euclid's data will complement other surveys like DES, KiDS, and the future Rubin Observatory LSST, providing a unique combination of depth, area, and wavelength coverage in the near-infrared.
Euclid's VIS instrument is a 36-CCD mosaic array with a total of 609 megapixels, sensitive in the 550–900 nm range, achieving a point-spread function of ~0.1 arcsecond. NISP operates in three near-infrared bands (Y, J, H) and uses a grism for slitless spectroscopy, providing redshifts for millions of galaxies. The telescope's thermal design keeps the optics at ~150 K, and the spacecraft uses a sunshield to maintain stability. Euclid's data processing pipeline is distributed across nine national data centers in Europe, with the Euclid Consortium handling calibration and science products. The mission has a nominal lifetime of six years, with consumables for up to eight, and its data releases are planned to be public after a proprietary period.
Euclid's name honors the ancient Greek mathematician Euclid, reflecting its goal to measure the geometry of the Universe. The mission was originally proposed as DUNE (Dark Universe Explorer) and later merged with SPACE (Spectroscopic All-sky Cosmic Explorer) to form Euclid. A notable technical challenge is the stray-light rejection: the telescope's baffles and sunshield are designed to minimize light from the Sun, Earth, and Moon, which would otherwise contaminate the faint galaxy images. Euclid also carries a small technical demonstration of laser communication, the Optical Communication Terminal, which successfully transmitted data at 50 Mbps from L2 to Earth in 2024. The mission's first early release observations, published in May 2024, showcased stunning images of the Perseus cluster and the Horsehead Nebula, demonstrating its capability to capture both deep cosmological fields and nearby objects.
Euclid is a cornerstone of ESA's Cosmic Vision programme, with data releases expected to transform cosmology.
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