The MOSAIC Consortium held its Science Meeting from October 27 to 29, 2025, at the Venture Studio, located in the Amsterdam Science Park.  More than 60 people attended the meeting in person (see Figure), and over 20 participated online. This meeting aimed to foster interactions within the Science Team and to initiate the preparation of the MOSAIC Red Book, which is expected to be finalized by mid-2027 at the latest. The main objectives were achieved, namely: (i) to inform the team about the project status, science plans, and latest developments in the instrument design; (ii) to encourage interactions and synergies between MOSAIC and other major projects in spectrocopy; and (iii) to discuss new technical and scientific developments that may impact the operation of MOSAIC, in particular for the exploitation of the GTO.

Group of in person participants in front of the LAM (16-18/09/2025)

The workhorse instruments of the current 8-10m class observatories are multi-object spectrographs (MOS), providing comprehensive follow-up of ground-based and space-borne imaging data. With the advent of even deeper imaging surveys from, e.g., HST, VISTA, JWST and Euclid, many science cases require complementary spectroscopy with high sensitivity and good spatial resolution to identify the objects and to measure their astrophysical parameters. The light-gathering power of the 39m ELT and its spatial resolution, combined with a MOS, will enable the large samples necessary to tackle some of the key scientific drivers of the ELT project, ranging from studies of stellar populations out to the highest-redshift galaxies. Consequently, a MOS-facility is foreseen within the ELT instrumentation plan.

Progress Meeting no. 3 took place at LAM (Marseille) in december 2023