The two studies use different methodologies. Fraser et al. collected data from five different surveys spanning six nights. Drahus et al. used ~8 hours of observations taken in the course of two days from the Gemini North telescope. These two approaches are complementary: the former gives a longer time series but has more sources of uncertainty as each telescope suffers from different systematics; the latter covers a shorter time — an important factor when hunting for rotational irregularities — but the data come from the same telescope. In any case, they both reach the same conclusions. In addition to the tumbling, they also detect huge brightness variations per rotation, almost 2.5 magnitudes, larger than any other Solar System body and from which the inferred highly elongated shape of the object comes from.
But why is the tumbling property so interesting? Tumbling small bodies are an extreme minority in the Solar System: usually, damping mechanisms regularize the rotation. The tumbling state is thus a window on ’Oumuamua’s history: at a certain moment, something happened and induced a lasting perturbation. According to Drahus et al., the most probable cause is a violent collision. The other main mechanism to generate tumbling, sublimation torques, works only on active cometary-like bodies and ’Oumuamua didn’t show any activity when it flew close to the Sun. Fraser et al. suggest that ’Oumuamua must be quite rigid, otherwise it would have been dampened already, and the tumbling event may have happened in its home system.
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