The European Space Agency’s (ESA’s) Euclid space telescope is now on its way to its permanent operating location, some 1.5-million kilometres from Earth (or four times the distance to the Moon), known as Sun-Earth Lagrange point 2 (L2). This is point of gravitational equilibrium between the Sun and the Earth, in the direction opposite to the Sun. The telescope, which was launched on a SpaceX Falcon 9 rocket from US Space Force Station Cape Canaveral on Saturday, will orbit around Sun-Earth L2.

“[W]e celebrate the successful launch of a ground-breaking mission that places Europe at the forefront of cosmological studies,” enthused ESA science director Carole Mundell. “If we want to understand the Universe we live in, we need to uncover the nature of dark matter and dark energy and understand the role they played in shaping our cosmos. To address these fundamental questions, Euclid will deliver the most detailed map of the extra-galactic sky. This inestimable wealth of data will also enable the scientific community to investigate many other aspects of astronomy, for many years to come.”

Scientists currently believe that dark matter accounts for 85% of the matter in the Universe, and that “normal” (or baryonic) matter accounts for only 15%. But dark matter only interacts with baryonic matter by means of gravity, which is the weakest of the fundamental forces. It is called dark matter because it neither reflects nor absorbs light, and so is invisible on all wavelengths of the electromagnetic spectrum. Dark energy is even more mysterious. It is the energy that drives the accelerating expansion of the universe. Of all the Universe’s energy and matter combined (and not just the matter), dark energy accounts for some 68% of the total, with dark matter contributing about 27% and baryonic (“normal”) matter less than 5%.

Euclid has a 1.2-m-diameter reflecting telescope that feeds two scientific instruments, described by ESA as “innovative”. These are the visible-wavelength camera (VIS) and the Near-Infrared Spectrometer and Photometer (NISP). It will enter orbit around L2 in four weeks, and then its telescope will be aligned and its instruments turned on. An instrument testing and evaluation phase will then follow, and the telescope will start operations three months from now.

The telescope will observe billions of galaxies, out to a distance of 10-billion light years. It will chart the shape, position and movement of these galaxies, revealing the distribution of matter across the Universe and how the expansion of the Universe developed over cosmic time. The map it will produce will be the largest and most accurate map of the Universe yet created, a map which will include the dimension of time. This data will allow scientists to infer the properties of dark energy and dark matter.

“The big mystery of the fundamental constituents of the Universe is staring us in the face, offering a formidable challenge,” observed Euclid project scientist René Laureijs. “Thanks to its advanced telescope and powerful scientific instrumentation, Euclid is poised to help us unravel this mystery.”  

Led by ESA, the Euclid programme involves significant international participation. The US National Aeronautics and Space Administration provided the detectors for the NISP. And both the NISP and VIS were contributed by the Euclid consortium, which is composed of more than 2 000 scientists in more than 300 institutes, spread across Europe, Canada, Japan and the US.