1. Maddox, J. Nature 346, 311 (1990).
2. Joos, F., Sarmiento, J. L. & Siegenthaler, U. Nature 349, 772–775 (1991).
3. McKay, C. P. (ed.) The Case for Mars II, Am. Astronaut. Soc. Sci. Technol. Ser. Vol. 62 (Univelt, San Diego, 1985).
4. Stoker, C. R. (ed.) The Case for Mars III, Am. Astronaut. Soc. Sci. Technol. Ser. Vol. 74, 75 (Univelt, San Diego, 1985).
5. McKay, C. P. & Stoker, C. R. Rev. Geophys. 27, 189–214 (1989).