“The image shows 1000 galaxies belonging to the Perseus Cluster, and more than 100 000 additional galaxies further away in the background.”
One Euclid frame caught 1,000 galaxies in the Perseus Cluster and over 100,000 behind it, some whose light left 10 billion years ago. The mission has six years to map billions of galaxies and pin down dark matter and dark energy, which ESA says make up 95% of the cosmos. Nobody knows what either one is. The pretty pictures are the easy part.