1. Abdrakhimov, A.M., Basilevsky, A.T., Head, J.W., Robinson, M.S.: Luna 17/Lunokhod 1 and Luna 21/Lunokhod 2 Landing Sites as Seen by the Lunokhod and LRO Cameras. In: The 42nd Lunar and Planetary Science Conference, The Woodlands, Texas, March 7-11 (2011)
2. Arkhipov, A.V.: Earth-Moon System as a Collector of Alien Artefacts. Journal of the British Interplanetary Society 51, 181–184 (1998)
3. A’Hearn, M.F., et al.: Deep Impact: A Large-Scale Active Experiment on a Cometary Nucleus. Space Science Reviews 117, 1–21 (2005)
4. Balazs, B.S.: The Galactic belt of intelligent life. In: Marx, G. (ed.) Bioastronomy - The Next Steps, pp. 61–66. Kluwer Academic Publishers, Dordrecht (1988)
5. Ball, J.A.: Extraterrestrial intelligence - Where is everybody? In: Papagiannis, M.D. (ed.) The Search for Extraterrestrial Life: Recent Developments, pp. 483–486. D. Reidel Publishing Co., Dordrecht (1985)