1. Roger D. Launius, “ ‘Not Too Wild a Dream’: NASA and the Quest for Life in the Solar System,” Quest: The History of Spaceflight Quarterly 6 (Fall 1998): 17–27.
2. Audra J. Wolfe, “Germs in Space: Joshua Lederberg, Exobiology, and the Public Imagination, 1958–1964,” Isis 93 (June 2002): 183–205, quote on 185.
3. Richard A. Proctor, Other Worlds Than Ours: The Plurality of Worlds Studied Under the Light of Recent Scientific Researches (New York: J.A. Hill and Co., 1870), p. 94
4. Dale P. Cruikshank, "The Development of Venus Studies," in D. M. Hunten, L. Colin, T. M. Donahue, and V. I. Moroz, eds., Venus (Tucson: University of Arizona Press, 1983), pp. 1-9.
5. J. L. E. Dreyer, "Schiaparelli's Researches on the Rotation of Venus and Mercury," Monthly Notices of the Royal Astronomical Society 51 (February 1891): 246-49