矢野 創

Mars Dust Counter (MDC) is a light-weight (730g) impact-ionization dust detector on board NOZOMI, a Japanese Mars mission, which was launched on July 4th 1998. The main aim of MDC is to detect the predicted Martian dust rings / tori. It can also cover velocity-mass ranges of interplanetary and interstellar dust particles. By August 2000, MDC had detected more than 60 dust particles. In 1999, it detected five fast particles probably of interstellar origin. For five years from 1999 to 2003, NOZOMI will orbit the sun and MDC can measure interplanetary and interstellar dust between the Earth's and Mars' orbits.

Detector characteristics of disk-shaped piezoceramic elements were studied by irradiating silver and carbon microparticles. A mass of particles ranged from 0.01 to 100pg, and whose velocity from 2 to 20km/s. We observed characteristic pulse signals when the particles were collided with the element. Carbon projectiles generated a bipolar-type sharp peak, whereas silver projectiles did not show such a distinct form. For silver, the pulse amplitude increased with increasing the particle energy. A possible application to a realtime detector of micrometeoroid and space debris is discussed.

We are at a unique point in our exploration of the solar system in which missions to obtain samples from Near- Earth Asteroids (NEAs) are both required by the progress of asteroid and meteorite research and are technologically feasible. Recent successes with the Deep Space 1 and NEAR-Shoemaker missions have resolved many of the technical challenges and the spectacular rate of discovery of new NEAs have provided an abundance of energetically favorable targets of a variety of compositional types. A sophisticated world-wide network of research and analysis laboratories and excellent curatorial facilities are already in place, and a protocol exists for ensuring adequate planetary protection. The breadth and depth of data that can be obtained from returned samples greatly exceeds that possible with in situ analysis, samples can be archived for future techniques and analysts, and crucial information will be available on source and context for the returned samples. The samples will provide new insights into the interpretation of the large amount of existing data about meteorites and asteroids and the origin of our solar system, the use of NEAs as natural resources to support the human exploration and development of space and the mitigation of asteroid impact on Earth. © 2001 The American Institute of Aeronautics and Astronautics Inc. All rights reserved.

Detector characteristics of disk-shaped piezoceramic elements were studied by irradiating silver and carbon microparticles. A mass of particles ranged from 0.01 to 100pg, and whose velocity from 2 to 20km/s. We observed characteristic pulse signals when the particles were collided with the element. Carbon projectiles generated a bipolar-type sharp peak, whereas silver projectiles did not show such a distinct form. For silver, the pulse amplitude increased with increasing the particle energy. A possible application to a realtime detector of micrometeoroid and space debris is discussed.

The MUSES-C, the near Earth object sample return mission will employ the impact sampling device, which has recently completed its flight model design and manufacturing. It implemented results from collection efficiency tests under the microgravity condition as well as contamination control protocols for returned samples.

Minor body mission plans in the post-MUSES-C era have been discussed since last year and the MEF has selected two finalists and integrated them with other candidates in terms of common scientific objectives and observational methods. These are the multiple rendezvous and sample return missions to spectral known near-Earth objects and the multiple fly-bys and sample returns to the main belt asteroid family members. We will discuss their preliminary mission plans, scientific objectives and expected results.

170 hypervelocity impact signatures on the MLI and SSM surfaces of the SFU spacecraft were studied their three dimensional morphology and elemental analysis to discriminate them by natural origin from those by artificial debris. Ratio of meteoroids against debris, with some "unknown" and "undetermined" origins, is compared to results from previously retrieved spacecraft. those of LDEF, EuReCa and HST. The impact flux on the Sun pointing face is also compared with (C) 1999 COSPAR. Published by Elsevier Science Ltd.

We have investigated in the laboratory the capture in aerogel (density 92.5 +/- 0.5 kg m(-3)) of small particles travelling at (5.1 +/- 0.2) km s(-1). The particles used were soda glass spheres and irregularly shaped olivine and iron particles, with mean diameters in the range 75-355 microns. We have measured the impact site for each particle, characterised by the mean diameter of the entrance hole in the aerogel, the minimum and maximum radii of the damaged region in the surface of the aerogel around the entrance hole, the length of the track in the aerogel caused by passage of the particle into the aerogel's interior, and the diameter of the captured particle (if seen) found near the end of the track. For each type of particle we establish relationships between the observed parameters and the pre-impact particle size. We find that the processes resulting in the observed surface features and the capture of the particles in the interior of the aerogel are different. We also find that the particle shape (spherical/irregular) does not unduly influence penetration depths in the aerogel. We have studied the effects of non-normal incidence on the observed impact features and find that the angle of incidence can be reconstructed to within +/-2 degrees. We compare the laboratory obtained data with that measured for four particles captured in a sample of aerogel flown in a Low Earth Orbit on board the EuReCa spacecraft. The density of one of the particles is predicted to be (1776 +/- 346) km m(-3). Using the ability to reconstruct impact direction the probable nature of the particles is shown to be micrometeoroids with retrograde trajectory. (C) 1999 Elsevier Science Ltd. All rights reserved.

We present the first ground-based observational evidence of the zodiacal dust bands originally discovered by the Infrared Astronomical Satellite (IRAS) and confirmed by the Cosmic Background Explorer (COBE). Our photometric observations have been performed on Mauna Kea, Hawaii, between 1997 October 29 and November 2, using a 24 mm wide-angle lens attached to a cooled CCD camera, and a blue filter centered at 440 nm. Photometric data of the morning zodiacal light have revealed the presence of zodiacal dust bands at ecliptic latitudes beta = 0 degrees, 3 degrees, and +/- 10 degrees, as well as additional faint structures at approximately beta = +/- 5 degrees, between solar elongations epsilon = 75 degrees and 90 degrees. The brightness of dust bands is approximately 2%-3% of the background zodiacal light. Moreover, our observation of the Gegenschein has discovered dust bands at beta = +2 degrees, -4 degrees, and -9 degrees at 165 degrees less than or equal to epsilon less than or equal to 185 degrees. Using the separation of the inner dust band pair observed in two different regions of epsilon, we estimate the parallactic distance of this band pair to be about 1.6 AU from the Sun.

Micrometeoroid detection in space usually involves high-velocity impact phenomena. In-situ dust detectors should be calibrated by a microparticle accelerator with a mass and velocity range comparable to micrometeoroids. A pilot model of an accelerator was constructed some years ago and fundamental research for an advanced facility has been performed. We are developing two new accelerators. A 3.75MV Van de Graaff electrostatic accelerator at The Research Center for Nuclear Science and Technology, University of Tokyo, has been modified to accelerate microparticles, and acceleration testing is now being carried but. The expected velocity range is 1-20 km/s for micron or sub-micron particles. Another small accelerator will be installed for easier handling, more frequent use, and lower-cost operation. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

For the purpose of simulating the surface alteration process called "space weathering", experiments of pulse laser irradiation, proton implantation, and laser irradiation to proton implanted samples were performed and reflectance spectra of altered materials were measured. To simulate the impact heating by micrometeorite bombardments, we made a new apparatus using a pulse laser whose pulse duration is 6-8 nanoseconds, comparable with a timescale of micrometeorite impacts. We find that the degree of space weathering, i.e., change of reflectance spectrum should depend on mineral composition. Laser irradiation onto olivine produces the largest reduction of albedo and the highest reddening of reflectance spectrum. In general, variation of olivine spectra is much larger than that of pyroxenes, Depths of absorption bands do not change in the scaled spectra, The olivine spectrum after the laser irradiation can match spectra of some olivine asteroids within a subtype of S-type asteroids. Comparison of Vesta spectrum with altered pyroxene spectra suggests that Vesta surface would be relatively older than olivine asteroids. We also investigate the influence of solar wind proton and pyroxene FeO content. The proton implantation causes small changes in olivine and enstatite spectra. Implanted protons do not influence spectral change by the laser irradiation: the laser irradiation and the proton implantation do not produce multiplicative but additive changes on the reflectance spectra, FeO content of pyroxenes does not relate to the degree of reflectance change.