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  Decreased values of cosmic dust number density estimates in the Solar System

Willis, M. J., Burchell, M. J., Ahrens, T. J., Krüger, H., & Grün, E. (2005). Decreased values of cosmic dust number density estimates in the Solar System. Icarus, 176(2), 440-452. doi:10.1016/j.icarus.2005.02.018.

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Willis, M. J.1, Author
Burchell, M. J.1, Author
Ahrens, T. J.1, Author
Krüger, H.2, Author           
Grün, Eberhard2, Author           
Affiliations:
1Lindhurst Laboratory of Experimental Geophysics, Seismological Laboratory, 252-21, 1200 E. California Blvd., California Institute of Technology, Pasadena, CA 91125, USA Centre for Astrophysics & Planetary Sciences, School of Physical Sciences, University of Kent, Canterbury, Kent CT2 7NR, UK Hawaii Institute of Geophysics and Planetology, University of Hawaii, 1680 East West Road, Honolulu, HI 96822, USA, ou_persistent22              
2Ralf Srama - Heidelberg Dust Group, Research Groups, MPI for Nuclear Physics, Max Planck Society, ou_907558              

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Free keywords: Interplanetary dust; Impact processes; Instrumentation; Experimental techniques
 Abstract: 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 km s-1, 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 km s-1 yield rise times 10–30% longer than for direct impacts, so that derived impact velocity is reduced by a factor of 2. Impacts on side wall at 20–50 km s-1 reduced rise times by a factor of 10 relative to direct impact data. This would result in serious overestimates of flux of particles intersecting the dust instrument at velocities of 20–50 km s-1. 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 km s-1 impacts, 27% at 10 km s-1 and 400% at 70 km s-1. We predict that individual particle masses are overestimated by 10–90% when side-wall impacts occur at 2–20 km s-1, and underestimated by 10–102 at 20–50 km s-1. We predict that wall impacts at 20–50 km s-1 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 9.4×10-5, 9.9×10-5, 4.1×10-5, and 6.8×10-5 m-3 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 1.6×10-4, 7.9×10-4, 3.2×10-5, 3.2×10-5, and 7.9×10-4 m-3 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.

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Language(s): eng - English
 Dates: 2005-08
 Publication Status: Issued
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: eDoc: 276591
DOI: 10.1016/j.icarus.2005.02.018
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Title: Icarus
Source Genre: Journal
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Pages: - Volume / Issue: 176 (2) Sequence Number: - Start / End Page: 440 - 452 Identifier: -