Jordi Portell, Ariel Goobar, Alain Léger, Barbara McArthur, Renaud Goullioud, Pat Scott, Carme Jordi, Katherine Freese, Douglas Spolyar, Antonaldo Diaferio, John A. Tomsick, Gary A. Mamon, Luisa Ostorero, Glenn J. White, Rory Barnes, Paulo J. V. Garcia, Eva Villaver, L. Chemin, Torsten A. Enßlin, Berry Holl, Warren R. Brown, Conrado Albertus, Malcolm Fridlund, Hamish A. Clark, Miguel de Val-Borro, Christophe Le Poncin-Lafitte, Fabien Malbet, Mariateresa Crosta, Jean-Pierre Prost, Ummi Abbas, Erik Høg, Celine Boehm, Morgane Fortin, Sergei A. Klioner, Ariane Lançon, Oleg Y. Gnedin, D. L. Harrison, Lukasz Wyrzykowski, Alcione Mora, Laura L. Watkins, Aldo S. Bonomo, Daniel Michalik, Philippe Thebault, Frederic Courbin, Nigel Hambly, Andrew D. Holland, Lucas Labadie, Micaela Oertel, Melvyn B. Davies, Manuel A.V. Ribeiro da Silva, Hervé Bouy, Andreas Quirrenbach, Alberto Krone-Martins, Wesley A. Traub, Rosemary F. G. Wyse, Vitor Cardoso, J. Schneider, Xavier Luri, Jeremy Darling, Marco Castellani, Arnaud Siebert, André Moitinho de Almeida, Matthew W. Muterspaugh, Mario G. Lattanzi, Neil J. Murray, A. J. Falcão, David Hobbs, Paulo Gordo, Mario Damasso, Monica Valluri, António Amorim, Jacques Laskar, Yoshiyuki Yamada, Mario Gai, Alexandre C. M. Correia, Leonidas A. Moustakas, João Alves, Alexis Brandeker, David Hall, Antonio da Silva, Guillem Anglada-Escudé, Nicholas A. Walton, Antoine Crouzier, Alessandro Sozzetti, M. Shao, A. Mourao, Malbet, F [0000-0002-8029-4226], Apollo - University of Cambridge Repository, National Aeronautics and Space Administration (US), Swiss National Science Foundation, Polish National Agency for Academic Exchange, Swedish National Space Agency, Fundação para a Ciência e a Tecnologia (Portugal), Australian Research Council, Agenzia Spaziale Italiana, Ministerio de Ciencia, Innovación y Universidades (España), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales [Toulouse] (CNES)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France -Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France, School of Physics [Sydney], The University of Sydney, CENTRA, Universidade de Lisboa, Queen Mary University of London (QMUL), Stockholm University, Ecole Polytechnique Fédérale de Lausanne (EPFL), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, UNINOVA / CTS, Campus FCT/UNL, University of Texas at Austin [Austin], Observatoire Astronomique de l'Université de Genève (ObsGE), Université de Genève = University of Geneva (UNIGE), University of Cologne, Institut d'astrophysique spatiale (IAS), Institut national des sciences de l'Univers (INSU - 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CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA), Université de Genève (UNIGE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), University of Granada [Granada], Smithsonian Institution-Harvard University [Cambridge], Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Università degli studi di Torino (UNITO), Universiteit Leiden [Leiden], Universidade do Porto, University of Copenhagen = Københavns Universitet (KU)-University of Copenhagen = Københavns Universitet (KU), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Thales Alenia Space [Cannes], Thales Alenia Space, University of California [Berkeley], University of California-University of California, Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7), Observatoire de Paris - Site de Paris (OP), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)
The authors would like to thank the researchers and engineers who are not coauthors of this paper but who have taken part and have brought their contribution to the proposed missions to ESA successive calls: NEAT (M3), micro-NEAT (S1), and Theia (M4 and M5). An extensive list of supporters for the science objectives is given in [17]. We thank also Arianna Gallo for her contribution in our investigation of the shape of the MilkyWay dark matter halo and Krzysztof A. Rybicki who generated the plots from Fig. 14. We are grateful to the anonymous referee who helped to improve the quality of the paper with his/her remarks. Concerning the funding of our work, we would like to acknowledge the support of many agencies or programs. R.B. acknowledges support from NASA’s Virtual Planetary Laboratory lead team under cooperative agreements NNA13AA93A. A.C.M.C. acknowledges support from CFisUC strategic project (UID/FIS/04564/2019). F.C. acknowledges support by the Swiss National Science Foundation (SNSF) and by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (COSMICLENS: grant agreement No. 787886). M.F. received support from Polish National Science Centre (NCN) under Grant No. 2017/26/D/ST9/00591. M.F. gratefully acknowledge the support of the Swedish National Space Agency (DNR 65/19, 174/18). D.H. thanks the Swedish National Space Agency (SNSA/Rymdstyrelsen) for their support. A.M. thanks the Portugese Fundac¸ ˜ao para a Ciˆencia e a Tecnologia (FCT) through the Strategic Programme UID/FIS/00099/2019 for CENTRA. P.S. acknowledges support from the Australian Research Council under grant FT190100814. L.W. acknowledges support from the Polish NCN grants: Harmonia No. 2018/06M/ST9/00311 and Daina No. 2017/27/L/ST9/03221. The OATo team acknowledges partial funding by the Italian Space Agency (ASI) under contracts 2014-025-R.1.2015 and 2018-24-HH.0, and by a grant from the Italian Ministry of Foreign Affairs and International Cooperation (ASTRA). A.C. and F.M. acknowledge support by the LabEx FOCUS ANR-11-LABX-0013. The work of C.J., X.L. and J.P. was supported by the Spanish Ministry of Science, Innovation and University (MICIU/FEDER, UE) through grants RTI2018-095076-B-C21, ESP2016-80079-C2-1-R, and the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia ’Mar´ıa de Maeztu’) through grants MDM-2014-0369 and CEX2019-000918-M. A.K.-M., A.A., V.C., P.G., P.G., A.M.A., A.M., M.S. were supported by Fundac¸ ˜ao para a Ciˆencia e a Tecnologia, with grants reference UIDB/00099/ 2020 and SFRH/BSAB/142940/2018 (P.G. only). A.D. and L.O. also acknowledge partial support from the Italian Ministry of Education, University and Research (MIUR) under the Departments of Excellence grant L.232/2016, and from the INFN grant InDark. G.J.W. gratefully acknowledges support of an Emeritus Fellowship from The Leverhulme Trust. EV is supported by Spanish grant PGC2018-101950-B-100. This research has made use of NASA’s Astrophysics Data System Bibliographic Services. Open access funding provided by Istituto Nazionale di Astrofisica within the CRUI-CARE Agreement., Sky survey telescopes and powerful targeted telescopes play complementary roles in astronomy. In order to investigate the nature and characteristics of the motions of very faint objects, a flexibly-pointed instrument capable of high astrometric accuracy is an ideal complement to current astrometric surveys and a unique tool for precision astrophysics. Such a space-based mission will push the frontier of precision astrometry from evidence of Earth-mass habitable worlds around the nearest stars, to distant Milky Way objects, and out to the Local Group of galaxies. As we enter the era of the JamesWebb Space Telescope and the new ground-based, adaptive-optics-enabled giant telescopes, by obtaining these high precision measurements on key objects that Gaia could not reach, a mission that focuses on high precision astrometry science can consolidate our theoretical understanding of the local Universe, enable extrapolation of physical processes to remote redshifts, and derive a much more consistent picture of cosmological evolution and the likely fate of our cosmos. Already several missions have been proposed to address the science case of faint objects in motion using high precision astrometry missions: NEAT proposed for the ESA M3 opportunity, micro-NEAT for the S1 opportunity, and Theia for the M4 and M5 opportunities. Additional new mission configurations adapted with technological innovations could be envisioned to pursue accurate measurements of these extremely small motions. The goal of this White Paper is to address the fundamental science questions that are at stake when we focus on the motions of faint sky objects and to briefly review instrumentation and mission profiles., NASA’s Virtual Planetary Laboratory NNA13AA93A, CFisUC strategic project (UID/FIS/04564/2019), Swiss National Science Foundation (SNSF), European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (COSMICLENS: grant agreement No. 787886), Polish National Science Centre (NCN) under Grant No. 2017/26/D/ST9/00591, Swedish National Space Agency (DNR 65/19, 174/18), Swedish National Space Agency (SNSA/Rymdstyrelsen), Portugese Fundacão para a Ciência e a Tecnologia (FCT) through the Strategic Programme UID/FIS/00099/2019 for CENTRA, Australian Research Council under grant FT190100814, Polish NCN grants: Harmonia No. 2018/06M/ST9/00311 and Daina No. 2017/27/L/ST9/03221, Italian Space Agency (ASI) under contracts 2014-025-R.1.2015 and 2018-24-HH.0, Italian Ministry of Foreign Affairs and International Cooperation (ASTRA), LabEx FOCUS ANR-11-LABX-0013, Spanish Ministry of Science, Innovation and University (MICIU/FEDER, UE) through grants RTI2018-095076-B-C21, ESP2016-80079-C2-1-R, Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia ’Mar´ıa de Maeztu’) through grants MDM-2014-0369 and CEX2019-000918-M, Fundacão para a Ciência e a Tecnologia, with grants reference UIDB/00099/ 2020 and SFRH/BSAB/142940/2018 (P.G. only), Italian Ministry of Education, University and Research (MIUR) under the Departments of Excellence grant L.232/2016, and from the INFN grant InDark, Emeritus Fellowship from The Leverhulme Trust, Spanish grant PGC2018-101950-B-100, Istituto Nazionale di Astrofisica within the CRUI-CARE Agreement