Fig. 5: The direction of the measured proton counts in MIPA and MIA angular field-of-view.

The azimuth and radial directions represent the azimuth and elevation angles in the MIPA instrument coordinate system. Each plot shows the log normalized counts in MIPA (red) and MIA (blue) instrument pixels, integrated over time and energy for (A) 13:58-13:59, (B) 13:55–13:58, and (C) 13:45–13:55. The yellow dots show the direction of Venus’ center (one per minute), and the orange dot shows the direction of the Sun. The measurements can be compared to the results from the LatHyS global hybrid model (Fig. 6), where we can extract the expected direction of the average bulk velocity (here shown as a blue dot) and the expected width of the proton distribution (shown as gray dots, calculated from the average thermal speed), at the location of BepiColombo in each time range. Note that the LatHyS bulk speed is lower than the LatHyS thermal speed in (A, B) (see Fig. 6C), and that the peak of the measured distribution in (C) is located within 20–30° of the bulk flow direction from LatHyS (blue dot) with significantly overlapping distributions, which both indicate a good match between the measurements and the simulations.