The European Extremely Large Telescope (E-ELT), i.e., ESO's future 39 meter telescope, will probably be the most ambitious ground-based optical astronomical facility of the century. Its main scientific objectives are the detection and study of the formation of the very first structures in the early Universe, 10-13 billion years ago, and obtaining the very first images of super exo-Earths and more generally the systematic characterization of extrasolar planets and their formation process.

The E-ELT is particularly innovative since it proposes for the first time to integrate the concept of adaptive optics directly within the telescope (Ground Layer Adaptive Optics, GLAO), which will provide uniform image quality and reduce the dependence of the observations to atmospheric conditions. Its great collecting power will reach sensitivities unmatched by any competing american ELT project. It will provide european astronomers with the most ambitious optical astronomical observation tool and the most powerful telescope ever built.

A fundamental prediction of cosmological models is that structures evolved "hierarchically" by successive mergers of more and more massive objects from the Big Bang to the galaxies we see around us today. Questions such as what seeded the growth of the first primordial galaxies and the history of galaxies like our own Milky Way remain unclear - only the ELT can bring the answers within our reach.

A major challenge is awaiting astronomers: the Universe contains hundreds of billions of galaxies, each of which consists of hundreds of billions of stars! Surveying these these systems efficiently calls for a multi-object spectrograph (MOS) as soon as possible after first light of the ELT in 2024.

The international MOSAIC Consortium, coordinated by Paris Observatory, is gathering together efforts across Europe and Brazil to build this ELT survey machine. It includes major players in instrument development and conception, which built a number of effective and scientifically productive instruments for the VLT (FLAMES, KMOS, NACO, X-SHOOTER).

The most prominent objective of MOSAIC will be to conduct the first exhaustive inventory of matter in the distant Universe. This will lift the veil on how matter is distributed in and between distant galaxies, by accounting for all kinds of regular matter, comprising stars and different phases of gas, as well as so-called dark matter.

The MOSAIC design has also been driven by 7 core science cases (below), but with its design also strongly influenced by other cases developed by the community in the MOS White Paper to ensure we're as ready as possible for the exciting discoveries awaiting in the late 2020s.

MOSAIC will give a tremendous leap forward in our understanding of how present-day galaxies formed and evolved. This includes detecting nearby primordial stars, the very first galaxies at the epoch of re-ionization, the most exhaustive dynamical survey of distant galaxies ever undertaken, and detailed study of stars in galaxies millions of light years beyond the Milky Way.

A massive work was initiated in 2011 to establish the scientific cases (hereafter, SCs) that are driving the design of a MOS on the E-ELT. Going from the largest to the smallest spatial scales :

  • ‘First light’ : MOSAIC will detect and study the very first galaxies. Their light, which has taken more than 13 billion years to reach us, will provide us with vital clues to our understanding of the early epoch when the Universe was ‘reionised’, during which its gas changed from a universally neutral into an ionised state.
  •  ‘Mapping the inter-galactic medium’ : The warm and hot gas between galaxies and within their halo is a reservoir of matter from which proto-galaxies can form. MOSAIC will provide an unprecedented map of the distant 3D structures of this gas as well as evaluating for the first time the distribution of the different baryonic components of the matter.
  • ‘Galaxy evolution with cosmic time’ : MOSAIC will dissect galaxies over the full lifetime of the observable Universe, providing us with vital information on their physical and chemical properties. The MOSAIC HDM will also provide well sampled rotation curves measuring the dark matter content of massive galaxies up to z=4. MOSAIC will be unrivalled when studying lower mass ‘dwarf’ and low-surface brightness galaxies, which play a major role in shaping galaxy evolution in the frame of the hierarchical scenario.
  •  ‘Super-massive black holes’ : A key question for astronomers is how the growth of super-massive black holes (thought to be at the heart of most present-day galaxies) and their host galaxies are self-regulated by feedback processes. These could be related to massive outflows driven by active galactic nuclei (AGN) and supernova explosions. MOSAIC will provide the first meaningful samples of galaxies in which the physical and geometrical parameters of such outflows will be measured.
  •  ‘Stellar populations in the Milky Way and beyond’ : The evolutionary history of galaxies is imprinted on their stellar populations, via their ages, chemical abundances, and kinematics. Spectroscopy is the only way to obtain robust estimates of these properties, to confront theoretical models of galaxy evolution. MOSAIC will study the oldest stellar populations in the Milky Way and nearby galaxies, providing a unique and direct connection to the physical conditions in the first galaxies. It will also observe individual stars in galaxies out to tens of Mpc, exploring an unprecedented range in stellar environments and providing direct estimates of chemical abundances for a large volume of the local Universe.
  • ‘Exploring the centre of the Milky Way’ : One of the most spectacular results of the past decade was arguably the observed orbits of stars aroud Sgr A*, the massive black hole at the centre of our Galaxy. Surrounding this central region there are puzzling structures of gas, dust, and sites of associated star formation, but these remain out of reach of current facilities. MOSAIC will provide the first glimpse into the physical conditions in this elusive region.
  • ‘Planet formation in different environments’ : The number of exo-planets known is growing rapidly, but this is posing important questions regarding the importance of environment – specifically stellar density and metallicity – on their formation. MOSAIC will be able to undertake comprehensive radial-velocity studies of stars in considerably more diverse environments than currently possible, e.g., in open and globular clusters, spanning a widespread of densities and metallicities, at a range of distances from the centre of the Galaxy.

The first three science cases will have a strong impact on cosmology, including the formation of the first structures, the missing baryon problem and the evolution of dark matter from well established rotation curves up to z= 4. ?

MOSAIC on the E-ELT will make us achieve a real leap forward in our understanding of all these scientific cases as well as many others that are summarized in a community "White Paper" . The large range of its potential discoveries, from planets to the first galaxies and their environment, will make MOSAIC the most requested instrument on the E-ELT.


The MOSAIC science team contains more than 130 astronomers from across the globe, with contributions from:

  • Jose Afonso
  • David Alexander
  • Emilio Alfaro Navarro
  • Omar Almaini
  • Leonardo Almeida
  • Philippe Amram
  • Joana Ascenso
  • Hervé Aussel
  • Beatriz Barbuy
  • Nate Bastian
  • Giuseppina Battaglia
  • Arjan Bik
  • Beth Biller
  • Xavier Bonfils
  • Piercarlo Bonifacio
  • Nicolas Bouche
  • Rychard Bouwens
  • Enzo Brocato
  • Andy Bunker
  • Elisabetta Caffau
  • Karina Caputi
  • John Carter
  • Africa Castillo
  • Stephane Charlot
  • Laurent Chemin
  • Cristina Chiappini
  • Ana Chies Santos
  • Andrea Cimatti
  • Michele Cirasuolo
  • Yann Clenet
  • Francoise Combes
  • Sébastien Comeron
  • Christopher Conselice
  • Thierry Contini
  • Jean-Gabriel Cuby
  • Katia Cunha
  • Emanuele Daddi
  • Massimo Dall'Ora
  • Gavin Dalton
  • Ben Davies
  • Reinaldo deCarvalho
  • Alex deKoter
  • Karen Disseau
  • James Dunlop
  • Benoit Epinat
  • Chris Evans
  • Michele Fabrizio
  • Sofia Feltzing
  • Annette Ferguson
  • Mercedes Filho
  • Alexis Finoguenov
  • Fabrizio Fiore
  • Ewan Fitzsimons
  • Hector Flores
  • Adriano Fontana
  • Dimitri Gadotti
  • Anna Gallazzi
  • Jesus Gallego
  • Paulo Garcia
  • Eric Gendron
  • Emanuele Giallongo
  • Oscar Gonzalez
  • Damian Gratadour
  • Eva Grebel
  • Eike Guenther
  • François Hammer
  • Chris Harrison
  • Vanessa Hill
  • Marc Huertas-Company
  • Rodrigo Ibata
  • Jorge Iglesia Paramo
  • Pascal Jagourel
  • Jure Japelj
  • Lex Kaper
  • Susan Kassin
  • Pierre Kervella
  • Andreas Korn
  • Davor Krajnovic
  • Rolf Kudritzki
  • Thierry Lanz
  • Soeren Larsen
  • Olivier LeFevre
  • Bertrand Lemasle
  • Jose Manuel Vilchez
  • Claudia Maraston
  • Justyn Maund
  • Iain Mcdonald
  • Ross McLure
  • Simona Mei
  • Simon Morris
  • Goran Ostlin
  • Stephane Paltani
  • Thibaut Paumard
  • Roser Pello
  • Laura Pentericci
  • Celine Peroux
  • Patrick Petitjean
  • Janine Pforr
  • Nor Pirzkal
  • Henri Plana
  • Mathieu Puech
  • Philipp Richter
  • Myriam Rodrigues
  • Emmanuel Rollinde
  • Martin Roth
  • Daniel Rouan
  • Gerard Rousset
  • Lee R. Patrick
  • Heikki Salo
  • Hugues Sana
  • Ruben Sanchez
  • Daniel Schaerer
  • Ricardo Schiavon
  • Rainer Schödel
  • Matthias Steinmetz
  • Mark Swinbank
  • William Taylor
  • Eduardo Telles
  • Goncalves Thiago
  • Christina Thöne
  • Scott Trager
  • Laurence Tresse
  • Miguel Verdugo
  • Susanna Vergani
  • Aprajita Verma
  • Jakob Walcher
  • Jianling Wang
  • Niraj Welikala
  • Lutz Wisotzki
  • Yanbin Yang
  • Stefano Zibetti
  • Bodo Ziegler

Who are we? Infos on the MOSAIC consortium.


Scientific goals and milestones: why MOSAIC?


How do we get there? All the technology behind MOSAIC.


What performance can we expect from MOSAIC?


How will MOSAIC fit in the instrumental landscape?