The SMART-1 lunar impact

The SMART-1 spacecraft impacted the Moon on 3rd September 2006 at a speed of 2 km s−1 and at a very shallow angle of incidence (∼1°). The resulting impact crater is too small to be viewed from the Earth; accordingly, the general crater size and shape have been determined here by laboratory impact experiments at the same speed and angle of incidence combined with extrapolating to the correct size scale to match the SMART-1 impact. This predicts a highly asymmetric crater approximately 5.5–26 m long, 1.9–9 m wide, 0.23–1.5 m deep and 0.71–6.9 m3 volume. Some of the excavated mass will have gone into crater rim walls, but 0.64–6.3 m3 would have been ejecta on ballistic trajectories corresponding to a cloud of 2200–21,800 kg of lunar material moving away from the impact site. The shallow Messier crater on the Moon is similarly asymmetric and is usually taken as arising from a highly oblique impact. The light flash from the impact and the associated ejecta plume were observed from Earth, but the flash magnitude was not obtained, so it is not possible to obtain the luminous efficiency of the impact event.