After launch in July 1998, more than 60 dust particles were detected by MDC on the Japanese Mars Mission NOZOMI (formerly PLANET-B) by August 2000. In 1999 during the cruise phase, MDC detected at least five high-velocity dust particles of interstellar origin. Interstellar dust particles entered the region inside the Martian orbit. MDC-NOZOMI will continue observing interplanetary and interstellar dust particles. From the beginning of 2004 for at least two years, MDC will enter Martian orbit and investigate proposed existence of dust rings or tori around Mars.
Figure .3. Dust impacts detected by MDC in 1999. Orbits of NOZOMI, the Earth, and Mars are shown on the ecliptic plane. +x direction is the direction of the sun at vernal equinox. NOZOMI takes an elliptic orbit whose perihelion is the Earth's orbit and aphelion is Mars' orbit. NOZOMI reached Mars' orbit in October. For each impact, the direction of the MDC sensor is expressed by a line from the impact mark. The length of each line corresponds to velocity. The big arrow denotes the direction of the interstellar medium towards the solar system, (a) Direction of MDC sensor aperture and impact velocity (i.e. relative velocity between NOZOMI and a dust particle), (b) Velocity of dust in the interplanetary space calculated from impact velocity and orbital velocity. Dust particles with high velocity (>40 km s"1) are expressed by bold lines.
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