Mars Dust Counter

抄録

In order to unveil the presence and characteristics of Martian dust ring/torus, Mars Dust Counter (MDC) is aboard ISAS's spacecraft PLANET-B, which will be launched in 1998 summer and investigate the upper atmosphere and surrounding environment of Mars between 1999 and 2001. MDC PLANET-B is an improved version of impactionization dust detectors aboard HITEN and BREMSAT. It weighs only 730 g with the sensor aperture area of 140 cm². To improve signal to noise ratios and to precisely determine the risetime of signals, a neutral target channel is added independent of ion and electron target channels. Detectable velocity (ν) range is between 1 km/s and more than 70 km/s, which will cover all possible dust clans: circummartian (low ν), interplanetary (mid ν), and interstellar (high ν) particles. Measurable mass range is 5 × 10^-15 and 10^-10 g at ν = 10 km/s. Since PLANET-B takes an elliptic retrograde orbit around Mars, MDC can investigate particles from Phobos and Deimos with relative velocity higher than 1 km/s. Therefore, MDC can clarify the presence of a confined dust ring along Phobos' orbit and an extended dust torus along Deimos' orbit, and it may answer whether these ring and torus are self-sustained or not. Since the nominal operation of PLANET-B is longer than one Martian year, MDC may detect predicted seasonal variation of the ring/torus structure.