| [ref.3] | Kuiper, G. P.: Visual Observations of Mars, 1956. Astrophys. J., vol. 125, 1957, p. 307. |
| [ref.4] | Föcas, J. H.: Seasonal Evolution of the Fine Structure of the Dark Areas of Mars. Planetary Space Sci., vol. 9, 1962, p. 371. |
| [ref.5] | Dollfus, A.: Interpretation of the Polarization of Light Reflected by the Different Regions of the Surface of Mars. Compt. Rend., vol. 233, 1951, p. 467. |
| [ref.6] | Kuiper, G. P.: On the Martian Surface Features. Publ. Astron. Soc. Pacific, vol. 67, 1955, p. 271. |
| [ref.7] | Sinton, W. M.: Spectroscopic Evidence for Vegetation on Mars. Astrophys. J., vol. 126, 1957, p. 231. |
| [ref.8] | Rea, D. G.; Belsky, T.; and Calvin, M.: Interpretation of the 3- to 4-Micron Infrared Spectrum of Mars. Science, vol. 141, 1963, p. 923. |
| [ref.9] | ([1], [2]) Rea, D. G.; O'Leary, B. T.; and Sinton, W.: Mars and the Origin of the 3.58- and 3.69-Micron Minima in the Infrared Spectra. Science, vol. 147, 1965, p. 1286. |
| [ref.10] | ([1], [2]) Quimby, F. H.: Concepts for Detection of Extraterrestrial Life. NASA SP-56, 1964. |
| [ref.11] | Urey, H. C.: The Planets. Their Origin and Development. Yale Univ. Press (New Haven), 1952. |
| [ref.12] | ([1], [2]) Miller, S. L.: Mechanism of Synthesis of Amino Acids by Electric Discharge. Biochim. Biophys. Acta, vol. 23, 1957, p. 480. |