1. Stevenson, D. J. Nature 298, 142–144 (1982).
2. Squyres, S., Reynolds, R. T., Cassen, P. M. & Peale, S. J. Icarus 53, 319–331 (1983).
3. McKinnon, W. B. in Proc. N.A.T.O. Research Workshop on Ices in the Solar System (ed. Klinger, J.) (in the press).
4. Herkenhoff, K. E. & Stevenson, D. J. Proc. 15th Lunar Planets Conf., Houston (1984).
5. Haff, P. K. Proc. Symp. Thin Film Interfaces and Interactions (eds Baglin, J. E. E. & Poate, J. M.) 21 (Electrochemical Society, Princeton, 1980).