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  • Cited by 3
  • Print publication year: 2015
  • Online publication date: November 2015

1 - Current approaches to finding life beyond Earth, and what happens if we do

from Part I - Motivations and approaches: How do we frame the problems of discovery and impact?


Three broad approaches exist in the search for extraterrestrial biology: (1) discover life in the Solar System by direct exploration; (2) find chemical signatures for biology in the atmospheres of exoplanets; or (3) detect signals (radio or optical) transmitted by intelligent beings elsewhere. In this chapter I describe each of these approaches, and then elaborate the multiple ways that we might learn of technologically competent civilizations. I also discuss why society's immediate reaction to the discovery of extraterrestrial intelligence would be less dramatic than often assumed. In all three cases the search for life beyond Earth is the ultimate remote sensing project. With few exceptions (such as sample return missions) this is exploration at a distance. While some reconnaissance is done by spacecraft, the majority of the effort consists of sifting through information brought to us in a storm of photons, either optical or radio.


The idea of extraterrestrial biology is hardly new, with written speculation on the subject dating back two millennia and more (Dick, 1982). The first scientific searches are more recent, beginning with Johannes Kepler who, observing the Moon in detail through an early telescope, thought he recognized features carved by rivers. These, he reasoned, were sure signs of biology. Kepler also believed that craters were the surface manifestations of underground cities constructed to protect the citizenry from the relentless sunshine of the two-week lunar day (Dick 1982, 75–77; Basalla 2006, 21).

These pioneering observations were plagued by naïve, anthropocentric assumptions and a lack of information on the true environments on these worlds. Such bugaboos continued to affect attempts to find cosmic company for centuries, extending to the enthusiastic study of Mars by astronomer Percival Lowell. In a series of books, lectures, and articles extending from 1894 until his death in 1916, Lowell proclaimed the existence of a vast, hydraulic civilization on the Red Planet (Crowe 1986; Dick 1996). Just as Kepler had done, he appealed to morphological evidence – straight-line features that he interpreted as canals – to back up these assertions. Lowell's claims were spurious, although one could argue that the falsity of his discoveries was due more to poor observation than poor interpretation (the trap that had snared Kepler). If the linear features described by Lowell actually existed, they would have been compelling evidence for intelligent beings.

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Arnold, L. 2013. Transmitting signals over interstellar distances: three approaches compared in the context of the Drake equation. International Journal of Astrobiology, 12:212–17.
Basalla, G. 2006. Civilized Life in the Universe: Scientists on Intelligent Extraterrestrials. New York, NY: Oxford University Press.
Brandt, T. and Spiegel, D. 2014. Prospects for detecting oxygen, water and chlorophyll on an exo-Earth. Proceedings of the National Academy of Sciences, 111:13278–83.
Carrigan, R. 2009. IRAS-based whole-sky upper limit on Dyson spheres. Astrophysical Journal, 698:2075.
Consolmagno, G. 2007. Personal communication, January 29.
Crowe, M. 1986. The Extraterrestrial Life Debate, 1750–1900. The Idea of a Plurality of Worlds from Kant to Lowell. Cambridge: Cambridge University Press.
Dick, S. J. 1982. Plurality of Worlds: The Origins of the Extraterrestrial Life Debate from Democritus to Kant. Cambridge: Cambridge University Press.
Dick, S. J. 1996. The Biological Universe: The Twentieth Century Extraterrestrial Life Debate and the Limits of Science. Cambridge: Cambridge University Press.
Drake, F. D. 1961. Project Ozma. Physics Today, 14:140.
Kardashev, N. 1964. Transmission of information by extraterrestrial civilizations. Soviet Astronomy, 8:217.
Learned, J., Kudritzki, R.-P., Pakvasa, S., and Zee, A. 2008. The Cepheid Galactic Internet. arXiv:08090.0339v2
Levin, G. and Straat, P. 1977. Life on Mars? The Viking Labeled Release Experiment. Biosystems, 9:165–74.
Livescience. 2012. One-third of Americans believe in UFOs, survey says. Accessed October 19, 2014.
Mayr, E. 1995. Can SETI succeed? Not likely. Bioastronomy News 7.
McKay, D., Gibson, E. K. Jr.Thomas-Keprta, K. L., et al. 1996. Search for past life on Mars: possible relic biogenic activity in Martian meteorite ALH84001. Science, 273: 924–930.
Navarro-Gonzalez, R.Vargas, E., de la Rosa, J., Raga, A. C, McKay, C. P. 2010. Reanalysis of the Viking results suggests perchlorate and organics at mid-latitudes on Mars. Journal of Geophysical Research, 115, E12010.
Petigura, E., Howard, A. and Marcy, G. 2013, Prevalence of Earth-size planets orbiting Sun-like stars. Proceedings of the National Academy of Sciences, 110:19273–78.
Rose, C. and Wright, G. 2004. Inscribed matter as an energy efficient means of communication with an extraterrestrial civilization. Nature, 431:47–9.
Rosenbaum, D., Maier, R., and Lavrakas, P. 1980. Belief in extraterrestrial life: a challenge to Christian doctrine and fundamentalists?Journal of UFO Studies, 2, 47–57.
Sholomitsky, G. B. 1965. “Variability of the Radio Source CTA-102.” Soviet AJ, 9:516.
Shostak, S. 2009. Confessions of an Alien Hunter. Washington, DC: National Geographic.
Shostak, S. 2011. “Short-pulse SETI,” Acta Astronautica, 68:362–65.
Shostak, S. 2012. “How to Find Extraterrestrial Life,” Huffington Post, July 5. Accessed October 20, 2014.
Tough, A. 2011. “Invitation to ETI.” Accessed October 19, 2014.
University of Wisconsin-Madison. 2014. “Ice Cube.” Accessed October 10, 2014.