Other
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt.........9j&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF FLORIDA, 1995.Source: Dissertation Abstracts International, Volume: 56-11, Section: B, page: 6171
Other
3
Asteroidal Dust
Scientific paper
We present the results of a detailed analysis of the Infrared Astronomical Satellite (IRAS) observations of the background zodiacal cloud. We have determined the planes of symmetry of the zodiacal cloud in three wavebands (12, 25 and 60mum) and have also measured the intriguing trailing/leading asymmetry in the peak flux of the zodiacal cloud at a solar elongation of 90^circ found in the IRAS data by Denott et al. (1987). In order to understand the source of the flux asymmetry, we have investigated the dynamical behavior of dust in the zodiacal cloud. Numerical integrations of the orbits of a large number of particles from the asteroid belt show that the dust particles created by collisions among asteroids spiral in towards the sun due to solar radiation forces. The drag rate for particles less than about 10mum in diameter is too high for resonance capture, while particles greater than about 100mum in diameter are destroyed by collisions with other particles before they reach the Earth. Therefore as particles in the size range of interest (10-100mum) approach the Earth, a significant fraction of the particles are trapped in the Earth's outer mean motion resonances that cause a bottleneck in the flow of particles to the sun. We have modeled the resulting local enhancement of the particle number density around the Earth's orbit and found that the resonantly trapped particles form a ring of dust around the sun with the Earth embedded in a cavity in the ring. Furthermore, the ring contains a cloud of dust that corotates with the Earth in its wake. This provides the first physical explanation for the observed trailing/leading asymmetry in the zodiacal cloud flux. We have studied the formation and structure of this ring and used it to estimate the asteroidal contribution of dust to the zodiacal cloud. This has been achieved by combining the ring with a background cloud model and comparing it with IRAS observations. We have also conducted an extensive numerical study of resonant trapping as theoretical calculations are not valid for particles with high drag rates. Moreover, the escape of particles from resonances are primarily due to close encounters with the Earth which is not taken into account by the theory. We have found that only particles greater than ~5mu m in diameter are captured into resonance and only sizes less than ~30mu m contribute to the asymmetry in the cloud. We believe that the flux the ring is associated with this limited range of particle sizes which can help us to constrain the particle size-frequency distribution near the Earth. Therefore the ring not only allows us to constrain parameters for the zodiacal cloud but also leads to a significantly improved model for the interplanetary dust emission.
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