MARS DUST COUNTER

In order to unveil the presence and characteristics of Martian dust ri ng/torus, Mars Dust Counter (MDC) is aboard ISAS's spacecraft PLANET-B , which will be launched in 1998 summer and investigate the upper atmo sphere and surrounding environment of Mars between 1999 and 2001. MDC PLANET-B is an improved version of impact-ionization dust detectors ab oard HITEN and BREMSAT. It weighs only 730 g With thp sensor aperture area nf 140 cm(2). To improve signal to noise ratios and to precisely determine the risetime of signals, a neutral target channel is added i ndependent of ion and electron target channels. Detectable velocity (v ) range is between I km/s and more than 70 km/s, which will cover all possible dust clans: circummartian (low v), interplanetary (mid v), an d interstellar (high v) particles. Measurable mass range is 5 x 10(-15 ) and 10(-10) g at v = 10 km/s. Since PLANET-B takes an elliptic retro grade 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 a n extended dust torus along Deimos' orbit, and it may answer whether t hese ring and torus are self-sustained or not. Since the nominal opera tion of PLANET-B is longer than one Martian year, MDC may detect predi cted seasonal variation of the ring/torus structure.