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

Willis, M. J. and Burchell, M. J. and Ahrens, T. J. and Krüger, H. and Grün, E. (2005) Decreased values of cosmic dust number density estimates in the Solar System. Icarus, 176 (2). pp. 440-452. ISSN 0019-1035. doi:10.1016/j.icarus.2005.02.018.

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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)∼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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Additional Information:© 2005 Elsevier Inc. Received 20 May 2004; Revised 17 January 2005; Available online 29 April 2005. The experimental work carried out here was supported by the UK Particle Physics and Astronomy Research Council (PPARC). The authors thank M. Cole for operation of the Van de Graaff accelerator. Contribution #9082, Division of Geological and Planetary Sciences, California Institute of Technology.
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Particle Physics and Astronomy Research Council (PPARC)UNSPECIFIED
Subject Keywords:interplanetary dusts; impact processes; instrumentation; experimental techniques
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Caltech Division of Geological and Planetary Sciences9082
Issue or Number:2
Record Number:CaltechAUTHORS:20141022-092814393
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Official Citation: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:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50671
Deposited On:22 Oct 2014 19:10
Last Modified:10 Nov 2021 18:59

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