Panel A: mean cosine of the solar incidence angle vs. rotation time of the likely emitting region (Fig. 7): the red interval ranges from about 4:35 h to 6:15 h, the time span in which the likely emitting region is illuminated.We selected 4:35 h because it corresponds to the peak of the cosine plot, while 6:15 h corresponds to the moment in which the region starts to move into shadow. The blue interval represents the observation time of the dust plume (7:42–7:48 h). We note that during the dust plume, the emitting region is completely in shadow. Panel B: source region of the night-side dust activity detected by VM. The red rectangle indicates the emitting region calculated with the method described in the first part of Sect. 5, with a latitude ranging from − 30° to +10° and a longitude from 265 to 280°. The green rectangle indicates the source region constrained by measuring the length of the plume shadow. The region is mainly in the Anuket and Hapi regions.