We thank the two anonymous referees for their kind comments which helped to improve the presentation of our results. We thank all the staff at the ESO La Silla Observatory for their support. A.R. and C.S. acknowledge support from the UK Science and Technology Facilities Council. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 870403 (NEOROCKS). This work was supported by the DART mission, NASA Contract No. 80MSFC20D0004. This research has received funding from the Europlanet 2024 Research Infrastructure (RI) program. The Europlanet 2024 RI provides free access to the world's largest collection of planetary simulation and analysis facilities, data services and tools, a ground-based observational network, and a program of community support activities. Europlanet 2024 RI has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 871149. N.P. acknowledges funding from Fundac & atilde;o para a Ciencia e a Tecnologia (FCT), Portugal, through the research grants UIDB/04434/2020 and UIDP/04434/2020. P.L.P. was partly funded by Programa de Iniciacion en Investigacion-Universidad de Antofagasta. INI-17-03. U.G.J., M.A., and F.A. acknowledge support from the European Union H2020-MSCA-ITN-2019 under grant No. 860470 (CHAMELEON) and the Novo Nordisk Foundation Interdisciplinary Synergy Programme grant No. NNF19OC0057374. D.B.L. and N.S.C.B. who are associated as co-authors of this manuscript are students of the program "Magister en Astronomia" (Universidad de Antofagasta). This paper uses Paul Tol's color schemes and templates: https://personal.sron.nl/~pault/. For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising from this submission.

The NASA’s Double-Asteroid Redirection Test (DART) was a unique planetary defence and technology test mission, the first of its kind. The main spacecraft of the DART mission impacted the target asteroid Dimorphos, a small moon orbiting the asteroid Didymos (65803), on 2022 September 26. The impact brought up a mass of ejecta which, together with the direct momentum transfer from the collision, caused an orbital period change of 33 ± 1 minutes, as measured by ground-based observations. We report here the outcome of the optical monitoring campaign of the Didymos system from the Danish 1.54 m telescope at La Silla around the time of impact. The observations contributed to the determination of the changes in the orbital parameters of the Didymos-Dimorphos system, as reported by Thomas et al., but in this paper we focus on the ejecta produced by the DART impact. We present photometric measurements from which we remove the contribution from the Didymos-Dimorphos system using an H-G photometric model. Using two photometric apertures we determine the fading rate of the ejecta to be 0.115 ± 0.003 mag day (in a 2″ aperture) and 0.086 ± 0.003 mag day (5″) over the first week postimpact. After about 8 days postimpact we note the fading slows down to 0.057 ± 0.003 mag day (2″ aperture) and 0.068 ± 0.002 mag day (5″). We include deep-stacked images of the system to illustrate the ejecta evolution during the first 18 days, noting the emergence of dust tails formed from ejecta pushed in the antisolar direction, and measuring the extent of the particles ejected Sunward to be at least 4000 km. © 2023. The Author(s). Published by the American Astronomical Society.

Full list of the authors: Rożek, Agata; Snodgrass, Colin; Jørgensen, Uffe G.; Pravec, Petr; Bonavita, Mariangela; Rabus, Markus; Khalouei, Elahe; Longa-Peña, Penélope; Burgdorf, Martin J.; Donaldson, Abbie; Gardener, Daniel; Crake, Dennis; Sajadian, Sedighe; Bozza, Valerio; Skottfelt, Jesper; Dominik, Martin; Fynbo, J.; Hinse, Tobias C.; Hundertmark, Markus; Rahvar, Sohrab; Southworth, John; Tregloan-Reed, Jeremy; Kretlow, Mike; Rota, Paolo; Peixinho, Nuno; Andersen, Michael; Amadio, Flavia; Barrios-López, Daniela; Castillo Baeza, Nora Soledad