Physics of large-scale impacts and planetary evolution

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Our projects are divided into four groups:(1) Study on the collisional probability of two particles moving around the Sun.(2) Experimental Study on the products of collisions and mass, energy, and rotational distributions of their fragments.(3) Study on the collisional degassing and collisional metamorphisim combining collision experiments and chemical, isotopical measurements.(4) Studies on the formation processes of the planets and meteorites, and the origin of the planetary atmosphere using the results obtained in subprojects (1) to (3).Before the start of this project, any studies on this field have not been developed and we were in very primitive stage of investigations. Thus, we cannot now have the whole, well-established results. However, during 3 years within which we have been supported by the grant-in-aid for scientific research, we have interesting and useful results for the future studies.As for subproject (1), we have succeeded in formulating mathematically the statistical behavior of the particles moving in the solar gravity. We are now under investigations of numerical orbital calculations; combining we will soon have final and extensive results on the collisional and scattering probabilities between particles. For subject (2), we have already obtained the general scaling law on the collisional behavior of colliding products and on the mass distribution of the collisional fragments. Also we have a preliminary results on the distribution of rotational frequency of the fragments. As to subproject (3), preliminary experiments and chemical measurements have been made with the results that the degassing rate is very small contrary to the result obtained by Ahrens et al. Finally, for subproject (4), we have proposed new scenario on the origin of the planetary atmosphere; terrestrial atmosphere and those of Venus and Mars. As a whole we are now in the course of complete understanding on this field and should continue to investigate in the future.