Dust measurements with the Mars Dust Counter on board Nozomi (PLANET-B)
Nozomi was Japan's first space mission to Mars, launched on 3 July 1998 UT. It was equipped with the Mars Dust Counter (MDC) which was an impact ionisation dust detector. MDC detected 96 dust particle impacts when the spacecraft was in Earth orbit and later in interplanetary space, before its operation ended in April 2002 due to a technical failure on board. We compare the Nozomi dust measurements with the dust measurements obtained with the dust detector on board the Ulysses spacecraft. Impact speeds and masses of dust particles measured by Nozomi MDC are overall consistent with the measurements obtained by Ulysses in the same region of interplanetary space. Based on the impact speeds measured while Nozomi was in Earth orbit, MDC detected neither dust particles of natural origin that were bound to the Earth nor space debris. The dust impact rate measured in interplanetary space varied by approximately a factor of 2, consistent with theoretical predictions by the Interplanetary Meteoroid Engineering Model. The particle impact direction was concentrated towards the ecliptic plane, in agreement with an interplanetary origin of the majority of the measured dust particles. No impacts of cometary trail particles could positively be identified during known cometary trail crossings of Nozomi. The Nozomi dust data may become a valuable reference for the dust measurements to be obtained in the same region of interplanetary space with future space missions like, for example, MMX and DESTINY$^+$.