Models of the Solar System’s evolution show that almost all the primitive material leftover from the formation of the planets was ejected to the interstellar space as a result of dynamical instabilities1. Accordingly, minor bodies should also be ejected from other planetary systems and should be abundant in the interstellar space2, giving hope for their direct detection and detailed characterization as they penetrate through the Solar System3,4. These expectations materialized on 19 October 2017 ut with the Panoramic Survey Telescope and Rapid Response System’s discovery of 1I/‘Oumuamua5. Here, we report homogeneous photometric observations of this body from Gemini North, which densely cover a total of 8.06 h over two nights. A combined ultra-deep image of 1I/‘Oumuamua shows no signs of cometary activity, confirming the results from other, less sensitive searches6,7,8,9. Our data also show an enormous range of rotational brightness variations of 2.6 ± 0.2 mag, larger than ever observed in the population of small Solar System objects, suggesting a very elongated shape of the body. Most significantly, the light curve does not repeat exactly from one rotation cycle to another and its double-peaked periodicity of 7.56 ± 0.01 h from our data is inconsistent with earlier determinations6,7,10,11,12. These are clear signs of a tumbling motion, a remarkable characteristic of 1I/‘Oumuamua’s rotation that is consistent with a collision in the distant past. Bearing marks of a violent history, this first-known interstellar visitor tells us that collisional evolution of minor body populations in other planetary systems might be common.
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The findings of this paper are based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy , Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil). We are indebted to the director of the Gemini Observatory, L. Ferrarese, for rapid evaluation and approval of our director’s discretionary time request. We also thank our telescope operator, A. Smith, for excellent work including real-time brightness monitoring of the target, and other Gemini Observatory staff members for vital contributions to making the GMOS-N observations possible. Special thanks to the ‘Alopeke instrument team for flexibility and cooperation during the observations, which disrupted their commissioning work. M.D., P.G. and B.H. are grateful for support from the National Science Centre of Poland through SONATA BIS grant number 2016/22/E/ST9/00109 to M.D.