Artist's impression of the Euclid spacecraft.

Euclid is a medium-class mission in ESA's Cosmic Vision to investigate the expansion of our Universe over the past ten billion years, probing cosmic epochs from before the expansion started to accelerate, all the way to the present.

In the background, a composite image of the massive galaxy cluster MACS J0717.5+3745 based on X-ray data from NASA's Chandra X-ray Observatory (shown in blue and purple hues) and optical observations performed by the NASA/ESA Hubble Space Telescope.