ESO signs MOSAIC deal for Extremely Large Telescope spectrograph

by Robert Schreiber
Potsdam, Germany (SPX) Dec 12, 2025

The European Southern Observatory ESO has signed an agreement with a large international consortium for the design and construction of the Multi-Object Spectrograph MOSAIC, an instrument for the Extremely Large Telescope ELT. On what will be the world's largest optical telescope, MOSAIC will simultaneously measure the light from hundreds of astronomical sources, tracing the growth of galaxies and the distribution of matter from the Big Bang to the present day. As a consortium member, the Leibniz Institute for Astrophysics Potsdam AIP is responsible for part of the technical development of MOSAIC and for preparing its scientific use.

"We are delighted that AIP, with its many years of expertise in multi-object spectroscopy, will be contributing to key work packages of MOSAIC. Our task is to develop and build the complex optical fibre system that will guide the starlight from the telescope to the spectrographs," says Dr Andreas Kelz, head of the 3D and Multi-Object Spectroscopy department at the AIP.

The agreement was signed by ESO's Director General Xavier Barcons and Alain Schuhl, the Deputy CEO for Science at the French National Centre for Scientific Research CNRS, the institution leading the MOSAIC consortium. Also in attendance were Alexandre Vulic TBC, the Consul General of France in Munich, MOSAIC Principal Investigator Roser Pello from the Marseille Astrophysics Laboratory and Co-Principal Investigator Mathieu Puech from the Paris Observatory, along with other representatives from ESO, CNRS and the MOSAIC consortium at ESO Headquarters in Garching, Germany.

MOSAIC is a spectrograph that splits light into its component wavelengths so astronomers can determine properties of astronomical objects such as chemical composition and temperature. The instrument will use the widest possible field of view provided by the ELT, will operate in visible and near-infrared light, and will analyse light from more than two hundred objects at the same time.

"MOSAIC will conduct the first exhaustive inventory of matter in the early Universe, lifting the veil on how matter is distributed within and between galaxies and greatly advancing our understanding of how present-day galaxies formed and evolved.", explains Dr Davor Krajnovic, the AIP representative on the MOSAIC science team and a coordinator of the consortium science working group "Inventory of matter". "It is a versatile instrument allowing studies of the first galaxies and the intergalactic medium, star formation and chemical enrichment histories, mass assembly of galaxies, dark matter, transient phenomena and discovering electromagnetic counterparts of multi-messenger events".

ESO's ELT is under construction in Chile's Atacama Desert, a site selected for its favourable observing conditions.