1. Benz, W., Slattery, W.L. & Cameron, A.G.W. Icarus 74, 516–528 (1988).
2. Wetherill, G. W. Science 228, 877–879 (1985).
3. Wetherill, G. W. in Origin of the Moon (eds Hartmann, W.K., Phillips, R.J. & Taylor G.J.) 519–550 (Lunar and Planetary Science Institute, Houston, 1986).
4. Wetherill, G.W. in Mercury (eds Chapman, C. & Vilas, F.) (University of Arizona Press, Tucson, in the press).
5. Lewis, J.S. Earth planet. Sci. Lett. 15, 286–290 (1972).