کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
10701964 | 1021223 | 2005 | 13 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Decreased values of cosmic dust number density estimates in the Solar System
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
علوم فضا و نجوم
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چکیده انگلیسی
Experiments to investigate the effect of impacts on side-walls of dust detectors such as the present NASA/ESA Galileo/Ulysses instrument are reported. Side walls constitute 27% of the internal area of these instruments, and increase field of view from 140° to 180°. Impact of cosmic dust particles onto Galileo/Ulysses Al side walls was simulated by firing Fe particles, 0.5-5 μm diameter, 2-50 kmâsâ1, onto an Al plate, simulating the targets of Galileo and Ulysses dust instruments. Since side wall impacts affect the rise time of the target ionization signal, the degree to which particle fluxes are overestimated varies with velocity. Side-wall impacts at particle velocities of 2-20 kmâsâ1 yield rise times 10-30% longer than for direct impacts, so that derived impact velocity is reduced by a factor of â¼2. Impacts on side wall at 20-50 kmâsâ1 reduced rise times by a factor of â¼10 relative to direct impact data. This would result in serious overestimates of flux of particles intersecting the dust instrument at velocities of 20-50 kmâsâ1. Taking into account differences in laboratory calibration geometry we obtain the following percentages for previous overestimates of incident particle number density values from the Galileo instrument [Grün et al., 1992. The Galileo dust detector. Space Sci. Rev. 60, 317-340]: 55% for 2 kmâsâ1 impacts, 27% at 10 kmâsâ1 and 400% at 70 kmâsâ1. We predict that individual particle masses are overestimated by â¼10-90% when side-wall impacts occur at 2-20 kmâsâ1, and underestimated by â¼10-102 at 20-50 kmâsâ1. We predict that wall impacts at 20-50 kmâsâ1 can be identified in Galileo instrument data on account of their unusually short target rise times. The side-wall calibration is used to obtain new revised values [Krüger et al., 2000. A dust cloud of Ganymede maintained by hypervelocity impacts of interplanetary micrometeoroids. Planet. Space Sci. 48, 1457-1471; 2003. Impact-generated dust clouds surrounding the Galilean moons. Icarus 164, 170-187] of the Galilean satellite dust number densities of 9.4Ã10â5, 9.9Ã10â5, 4.1Ã10â5, and 6.8Ã10â5mâ3 at 1 satellite radius from Io, Europa, Ganymede, and Callisto, respectively. Additionally, interplanetary particle number densities detected by the Galileo mission are found to be 1.6Ã10â4, 7.9Ã10â4, 3.2Ã10â5, 3.2Ã10â5, and 7.9Ã10â4mâ3 at heliocentric distances of 0.7, 1, 2, 3, and 5 AU, respectively. Work by Burchell et al. [1999b. Acceleration of conducting polymer-coated latex particles as projectiles in hypervelocity impact experiments. J. Phys. D: Appl. Phys. 32, 1719-1728] suggests that low-density “fluffy” particles encountered by Ulysses will not significantly affect our results-further calibration would be useful to confirm this.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Icarus - Volume 176, Issue 2, August 2005, Pages 440-452
Journal: Icarus - Volume 176, Issue 2, August 2005, Pages 440-452
نویسندگان
M.J. Willis, M.J. Burchell, T.J. Ahrens, H. Krüger, E. Grün,