Mathematics – Probability
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28q.445s&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 445
Mathematics
Probability
1
Accretion, Albedo, Dust, Interplanetary, Nebula, Nebula Midplane
Scientific paper
Sticking probability of fine particles is an important parameter that determines (1) the settling of fine particles to the equatorial plane of the solar nebula and hence the formation of planetesimals, and (2) the thermal structure of the nebula, which is dependent on the particle size through opacity. It is generally agreed that the sticking probability is 1 for submicrometer particles, but at sizes larger than 1 micrometer, there exist almost no data on the sticking probability. A recent study [1] showed that aggregates (with radius from 0.2 to 2 mm) did not stick when collided at a speed of 0.15 to 4 m/s. Therefore, somewhere between 1 micrometer and 200 micrometers, sticking probabilities of fine particles change from nearly 1 to nearly 0. We have been studying [2,3] sticking probabilities of dust aggregates in this size range using an optical sizing method. The optical sizing method has been well established for spherical particles. This method utilizes the fact that the smaller the size, the larger the angle of the scattered light. For spheres with various sizes, the size distribution is determined by solving Y(i) = M(i,j)X(j), where Y(i) is the scattered light intensity at angle i, X(j) is the number density of spheres with size j, and M(i,j) is the scattering matrix, which is determined by Mie theory. Dust aggregates, which we expect to be present in the early solar nebula, are not solid spheres, but probably have a porous fractal structure. For such aggregates the scattering matrix M(i,j) must be determined by taking account of all the interaction among constituent particles (discrete dipole approximation). Such calculation is possible only for very small aggregates, and for larger aggregates we estimate the scattering matrix by extrapolation, assuming that the fractal nature of the aggregates allows such extrapolation. In the experiments using magnesium oxide fine particles floating in a chamber at ambient pressure, the size distribution (determined by the method described above) was monitored over several hours and compared with the size distribution calculated from the growth equation (assuming sticking probability = 1) using an initial condition determine by the experiment. (This calculation takes into account the settling of the aggregates to the bottom of the chamber, which is actually observed in the experiments.) Comparison of the observed and the calculated size distribution shows that the observed size distribution is rather uniform in a restricted size range, while the calculated size distribution has a long tail at larger sizes. Such a difference in the size spectrum indicate that the sticking probability is smaller for larger aggregates. References: Blum J. and Munch M. (1993) Icarus, submitted. [2] Sugiura N. et al. (1991) LPSC XXII, 1355-1356. [3] Higuchi Y. et al. (1992) LPSC XXIII, 535-536.
Higuchi Yasunari
Sugiura Norimasa
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