On 18th November 1998, NOZOMI passed through the Leonid meteor stream, which was produced by Comet 55P/Tempel-Tuttle. Timing of the encounter between NOZOMI and the Leonid meteor tube was predicted to be about one day later than that of the Earth-Leonids encounter. Leonid dust could be easily distinguished by the estimated velocity and sensor direction. Just before the NOZOMI-Leonids encounter, MDC detected two clear impact signals. Preliminary estimates of impact velocity of both particles are 13 and 20 km s"1. NOZOMI is a spin-stabilized satellite and MDC is placed on one of its side panels. From pointing considerations the particle at 154 degree may belong to the Leonids, although the velocity is not as high as the encounter velocity with the Leonids of 70 km s"1.

3.2. Cruise Phase

After the fly-by with the Earth on December 20th 1998, NOZOMI entered a transfer cruise orbit toward Mars. A problem during the powered fly-by on the day, resulted in a change to the initial orbital plan to enter the circum-martian orbit in October 1999. Now NOZOMI will enter the circum-martian orbit on 1st January 2004 after a five-year cruise phase between the Earth's and Mars' orbits involving two fly-bys with the Earth. MDC detected nearly 40 dust particles in the cruise phase up to August 2000 (Table 1). As seen in Figure 2, MDC detected relatively high-velocity and low-mass particles compared with the circum-terrestira] phase.

Impact data in 1999 are projected into the ecliptic plane (Figure 3). Figure 3(a) shows the measured velocity of detected particles with sensor aperture direction. Figure 3(b) shows estimated velocity and direction of dust particles in space. MDC has detected at least 8 dust particles whose velocity is higher than 40 km s"1. This velocity, faster than the Keplerian

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