Mathematics – Logic
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..601g&link_type=abstract
European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a
Mathematics
Logic
Scientific paper
Dust is finely dispersed solid material in interplanetary space. It derives from a number of sources: larger meteoroids, comets, asteroids, the planets, and satellites, and there is interstellar dust sweeping through the solar system. These dust particles range in size from assemblages of a few molecules to tenth millimetre-sized grains. Dust particles absorb and scatter solar radiation and emit thermal radiation giving rise to Zodiacal light at visible and thermal emission at infrared wavelengths. Astronomical observations of both emissions provide information on the average properties of very large number of particles and their spatial distribution. Information on the physical and chemical properties and the orbital motion is obtained by direct methods. Direct methods include: (1) collection of dust particles (Fig. 1) on collectors on spacecraft returned to Earth and on airplanes in the stratosphere, (2) investigations of dust impacts craters on lunar samples and manmade impact plates returned from space, and (3) insitu measurements of individual particles by instruments on board satellites and space probes. Dust particles collected in the upper atmosphere provide the morphology and chemical and mineralogical composition of extraterrestrial particles of 5 to 50 microns in diameter but no information on the source of these particles is obtained. The NASA Stardust mission was the first space mission that returned dust from a comet. The study of impact craters on man-made and lunar surface samples exposed to space is used to characterize the flux of interplanetary micrometeoroids and their size distribution. Microcraters have been found ranging from 0.02 μm to millimetres in diameter. In-situ detectors on board of satellites and spaceprobes for the measurement of interplanetary dust have been used in the ecliptic plane from inside Mercury's orbit to the Kuiper belt and in space above and below the solar poles. Penetration detectors have a detection threshold of ≥10-13 g (approx. 1 μm radius). The most sensitive and versatile dust detectors are impact ionization detectors. They provide not only the mass and velocity of the impacting particle but also their chemical composition and electrical charge. Two types of dust particles were found to dominate the dust flux in interplanetary space. Interplanetary micrometeoroids covering a wide mass range from 10-16 to 10-6 g are mostly recorded at ecliptic latitudes below = 30º. Interstellar grains with masses between 10-14 and 10-12 g have been positively identified from 0.3 AU near the ecliptic plane and at high ecliptic latitudes (Fig. 2). Interstellar grains move on hyperbolic trajectories through the planetary system and constitute the dominant dust flux in the outer solar system and at high ecliptic latitudes. The interstellar dust stream is strongly filtered by solar radiation pressure and modulated by the solar wind magnetic field. Interstellar particles with optical properties of astronomical silicates or organic refractory materials are consistent with the observed radiation pressure effects. References [1] Jessberger, E. K. et al. (2001) In: Interplanetary Dust (eds. S.F. Dermott, H. Fechtig, E. Grün, and B.A.S. Gustafson): 253-294, Springer, Heidelberg [1] Grün et al. (2001) In: Interplanetary Dust (eds. S.F. Dermott, H. Fechtig, E. Grün, and B.A.S. Gustafson): 295-346, Springer, Heidelberg
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