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

Authors :
Willis, M.J.
Burchell, M.J.
Ahrens, T.J.
Kruger, H.
Grun, E.
Source :
Icarus. August, 2005, Vol. 176 Issue 2, p440, 13 p.
Publication Year :
2005

Abstract

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.02.018 Byline: M.J. Willis (a), M.J. Burchell (b), T.J. Ahrens (a), H. Kruger (c), E. Grun (d)(e) 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[degrees] to 180[degrees]. Impact of cosmic dust particles onto Galileo/Ulysses Al side walls was simulated by firing Fe particles, 0.5-5 [mu]m diameter, 2-50 kmas.sup.-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 kmas.sup.-1 yield rise times 10-30% longer than for direct impacts, so that derived impact velocity is reduced by a factor of [approximately equal to]2. Impacts on side wall at 20-50 kmas.sup.-1 reduced rise times by a factor of [approximately equal to]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 kmas.sup.-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 [Grun et al., 1992. The Galileo dust detector. Space Sci. Rev. 60, 317-340]: 55% for 2 kmas.sup.-1 impacts, 27% at 10 kmas.sup.-1 and 400% at 70 kmas.sup.-1. We predict that individual particle masses are overestimated by [approximately equal to]10-90% when side-wall impacts occur at 2-20 kmas.sup.-1, and underestimated by [approximately equal to]10-10.sup.2 at 20-50 kmas.sup.-1. We predict that wall impacts at 20-50 kmas.sup.-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 [Kruger 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 9.4x10.sup.-5, 9.9x10.sup.-5, 4.1x10.sup.-5, and 6.8x10.sup.-5m.sup.-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 1.6x10.sup.-4, 7.9x10.sup.-4, 3.2x10.sup.-5, 3.2x10.sup.-5, and 7.9x10.sup.-4m.sup.-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. Author Affiliation: (a) Lindhurst Laboratory of Experimental Geophysics, Seismological Laboratory, 252-21, 1200 E. California Blvd., California Institute of Technology, Pasadena, CA 91125, USA (b) Centre for Astrophysics & Planetary Sciences, School of Physical Sciences, University of Kent, Canterbury, Kent CT2 7NR, UK (c) Max-Planck-Institut fur Sonnensystemforschung, Max-Planck-StraAe 2, 37191 Katlenberg-Lindau, Germany (d) Max-Planck-Institut fur Kernphysik, Postfach 103980, 69029 Heidelberg, Germany (e) Hawaii Institute of Geophysics and Planetology, University of Hawaii, 1680 East West Road, Honolulu, HI 96822, USA Article History: Received 20 May 2004; Revised 17 January 2005

Subjects

Subjects :
Astronomy
Earth sciences

Details

Language :
English
ISSN :
00191035
Volume :
176
Issue :
2
Database :
Gale General OneFile
Journal :
Icarus
Publication Type :
Academic Journal
Accession number :
edsgcl.194025791