The schemes of the path of some particles are shown in figure 2. The scales in fragments a and b are approximately equal and correspond to the scale in figure 1. The scales in the fragments c and d in one order less. It is interesting to pay attention to the figure 2c. It is known [7] that without account of the Poynting-Robertson effect the motion near the collinear libration points is nearly elliptical with the center in the libration point. The case which is shown in figure 2c is the result of the perturbation action of the radiation which change the nature of the motion. On the existence of the dust screen near the L1 We can see that the dust cloud which filled in the small volume near L] will "spread" considerably after one year. Therefore, the dust screen which are placed in the libration point cannot be the reliable protection for the Earth during the long period. The instability shown for the examined dust screen in the point Lj does not exclude the principal possibility of such screen realization. However the requirement to its technical realization will be stronger in comparison with a stable case. Such a screen reliability will be in direct dependence on the dust refreshment frequency. The required time interval of the container escape into the libration point Lj is no more than one year. Acknowledgments The authors are greatly thankful to Dr. E. N. Polyakhova for the valuable discussion of results and critical comments on the manuscript. References 1. M. Mautner. Journal of The British Interplanetary Society. 44, 135, 1991. 2. J. Early. Journal of The British Interplanetary Society. 42,567, 1989. 3. A. V. Luk'yanov. Cosmic Research. 30, No. 1, 1992. 4. H. Robertson. Mon. Not. Royal Astron. Soc., 97, 423, 1937. 5. V. V. Radzievsky. Sov. Astron. Zh. 27, 250, 1950. 6. D. W. Schuerman. In: Solid Particles in the Solar System. IAU Symp. No.90, Ottawa, 27-30 August, 1979. D. Reidel Publ. Co., Dordrecht, Holland-Boston. 7. A. E. Roy. Orbital Motion. Adams Hilger Ltd., Bristol, 1978.
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