Discovery and physical characterization as the first response to a potential asteroid collision: The case of 2023 DZ(2)

Context. Near-Earth asteroids (NEAs) that may evolve into impactors deserve detailed threat assessment studies. Early physical characterization of a would-be impactor may help in optimizing impact mitigation plans. We first detected NEA 2023 DZ(2) on 27 February 2023. After that, it was found to have a minimum orbit intersection distance (MOID) with Earth of 0.00005 au as well as an unusually high initial probability of becoming a near-term (in 2026) impactor. Aims. We perform a rapid but consistent dynamical and physical characterization of 2023 DZ(2) as an example of a key response to mitigating the consequences of a potential impact. Methods. We used a multi-pronged approach, drawing from various methods (observational-computational) and techniques (spectroscopy-photometry from multiple instruments), and bringing the data together to perform a rapid and robust threat assessment. Results. The visible reflectance spectrum of 2023 DZ(2) is consistent with that of an X-type asteroid. Light curves of this object obtained on two different nights give a rotation period P = 6.2743 +/- 0.0005 min with an amplitude A = 0.57 +/- 0.14 mag. We confirm that although its MOID is among the smallest known, 2023 DZ(2) will not impact Earth in the foreseeable future as a result of secular near-resonant behaviour. Conclusions. Our investigation shows that coordinated observation and interpretation of disparate data provides a robust approach from discovery to threat assessment when a virtual impactor is identified. We prove that critical information can be obtained within a few days after the announcement of the potential impactor.