Development of the Mercury dust monitor (MDM) onboard the BepiColombo mission

In order to clarify the dust environment around Mercury, we have proposed that the Mercury dust monitor (MDM) should be onboard the BepiColombo/Mercury magnetosphere orbiter (MMO). The main objective of the project is to obtain new data on the flux and momentum of the interplanetary meteoroid complex near Mercury (0.31–0.47 AU). The MDM uses lightweight and heat-resistant piezoelectric ceramic sensors made of lead zirconate titanate (PZT). Four square plates of PZT, 40 mm×40 mm×2 mm each, will be installed on a side panel of the MMO. Upon colliding with a dust particle, the piezoelectricity of PZT generates a transient voltage signal. It is easy to determine the time of the impact event from which the incident direction is roughly estimated using the spin angle of the MMO. To extract kinetic information on incident particles from the output signals of the PZT sensor, calibration experiments have been carried out with hypervelocity dust particles from two Van de Graaff dust accelerators at the Max-Planck-Institut für Kernphysik and the University of Tokyo.