SERENA MFB1 scientific observations on Nature

30 November 2022

Recently published on Nature Communications the paper on the SERENA scientific observations during the first flyby at Mercury. PICAM and MIPA were operative during the whole passage and observations were performed nearby and inside Mercury’s magnetosphere. The flyby trajectory is shown in detail in Fig. 1. Closest approach occurred on October 1st 2021 at 23:34 UT at an altitude of 199 km above the planetary surface and at a ZMSM of about -0.7 RM in the nightside (Mercury Solar Magnetic frame). For comparison, Fig. 2 shows the whole set of BepiColombo flybys trajectories as well as the MESSENGER ones, plus the region covered by the NASA mission during its nominal phase (gray area): it can be noted that the first BepiColombo flyby at Mercury (and the second too) occurred in the southern hemisphere at low altitudes, a region never explored by previous missions.

Fig 1: The MFB1 trajectory of BepiColombo during the interval of interest: a in the XMSM-YMSM plane, b in the XMSM-ZMSM plane. The solid gray line represents the magnetopause surface, while the dashed gray line corresponds to the bow shock surface. Red lines correspond to the operational time of PICAM and MIPA sensors. Time labels are shown progressively along the trajectory.

Fig 2: The flyby trajectories of BepiColombo at Mercury projected onto the MSO frame, Z–ρ(z) plane (colored solid lines), compared to the MESSENGER flybys (dashed lines). The light grey area indicates the region covered by MESSENGER during its orbital mission phase (from Fig 27 in Mangano et al, 2021).

In particular, PICAM and MIPA observations covered the whole approaching phase, and the exiting phase (Fig. 1, red line in the trajectory). Fig. 3 shows a synthesis of the observations performed: PICAM operated during 4 distinct time periods and observed the solar wind ion flux (Panel a, insets 1 and 4), the inbound magnetosheath, and the inner magnetosphere (Panel a, insert 2), and the region upstream of the bow shock (Panel a, inset 3), while MIPA operated continuously from 22:35 UT to 23:56 UT, and observed the magnetosheath adjacent to the tail, the inner magnetosphere and the outbound magnetopause and bow shock (Panel b). An intermittent high-energy signal, possibly due to an interplanetary magnetic flux rope, has been observed downstream Mercury, together with low energy solar wind. Low energy ions, possibly due to satellite outgassing, were detected outside the magnetosphere. The dayside magnetopause and bow-shock crossing were much closer to the planet than expected, signature of a highly eroded magnetosphere. Different ion populations have been observed inside the magnetosphere, like low latitude boundary layer at magnetopause inbound and partial ring current at dawn close to the planet. A detailed description of the observations can be found here: https://www.nature.com/articles/s41467-022-34988-x

Fig. 3 The trajectory of BepiColombo during the interval of interest in the XMSM-RMSM plane: a PICAM observations, b MIPA observations. The solid gray line represents the magnetopause surface, while the dashed gray line corresponds to the bow shock surface. Red lines in a correspond to the operational time of PICAM, blue line in b corresponds to MIPA operation time. Time labels are shown progressively along the trajectory. Insets 1–4 in a show PICAM spectrograms for each specific time window, while the inset in b displays MIPA spectrograms. Color bars report ion counts in each specific time interval.