Observable tests for the light-sail scenario of interstellar objects

Context. Enigmatic dynamical and spectral properties of the first interstellar object (ISO), 1I/2017 U1 (Oumuamua), led to many hypotheses, including a suggestion that it may be an “artificial” spacecraft with a thin radiation-pressure-driven light sail. Since similar discoveries by forthcoming instruments, such as the Vera C. Rubin telescope and the Chinese Space Station Telescope (CSST), are anticipated, a critical identification of key observable tests is warranted for the quantitative distinctions between various scenarios. Aims. We scrutinize the light-sail scenario by making comparisons between physical models and observational constraints. These analyses can be generalized for future surveys of ‘Oumuamua-like objects. Methods. The light sail goes through a drift in interstellar space due to the magnetic field and gas atoms, which poses challenges to the navigation system. When the light sail enters the inner Solar System, the sideways radiation pressure leads to a considerable non-radial displacement. The immensely high dimensional ratio and the tumbling motion could cause a light curve with an extremely large amplitude and could even make the light sail invisible from time to time. These observational features allow us to examine the light-sail scenario of interstellar objects. Results. The drift of the freely rotating light sail in the interstellar medium is ~100 au even if the travel distance is only 1 pc. The probability of the expected brightness modulation of the light sail matching with ‘Oumuamua’s observed variation amplitude (~2.5–3) is