1. Bobrov, M. S.: 1970, in A. Dollfus (ed.),Surfaces and Interiors of Planets and Satellites, Academic Press, London and New York, p. 376.
2. Brahic, A.: 1977,Astron. Astrophys. 54, 895.
3. Brahic, A. and Sicardy, B.: 1981,Nature 289, 447.
4. Goldsmith, W.: 1960,Impact, Edward Arnold, London.
5. Hämeen-Anttila, K. A.: 1975,Astrophys. Space Sci. 37, 309.