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  • 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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The Impact of Discovering Life beyond Earth
  • Online ISBN: 9781316272480
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This list contains references from the content that can be linked to their source. For a full set of references and notes please see the PDF or HTML where available.

L. Arnold 2013. Transmitting signals over interstellar distances: three approaches compared in the context of the Drake equation. International Journal of Astrobiology, 12:212–17.

G. Basalla 2006. Civilized Life in the Universe: Scientists on Intelligent Extraterrestrials. New York, NY: Oxford University Press.

T. Brandt and D. Spiegel 2014. Prospects for detecting oxygen, water and chlorophyll on an exo-Earth. Proceedings of the National Academy of Sciences, 111:13278–83.

R. Carrigan 2009. IRAS-based whole-sky upper limit on Dyson spheres. Astrophysical Journal, 698:2075.

F. D. Drake 1961. Project Ozma. Physics Today, 14:140.

G. Levin and P. Straat 1977. Life on Mars? The Viking Labeled Release Experiment. Biosystems, 9:165–74.

D. McKay , E. K. Gibson Jr. K. L. Thomas-Keprta , et al. 1996. Search for past life on Mars: possible relic biogenic activity in Martian meteorite ALH84001. Science, 273: 924–930.

R. Navarro-Gonzalez E. Vargas , J. de la Rosa , A. C Raga , C. P. McKay 2010. Reanalysis of the Viking results suggests perchlorate and organics at mid-latitudes on Mars. Journal of Geophysical Research, 115, E12010.

E. Petigura , A. Howard and G. Marcy 2013, Prevalence of Earth-size planets orbiting Sun-like stars. Proceedings of the National Academy of Sciences, 110:19273–78.

C. Rose and G. Wright 2004. Inscribed matter as an energy efficient means of communication with an extraterrestrial civilization. Nature, 431:47–9.

S. Shostak 2011. “Short-pulse SETI,” Acta Astronautica, 68:362–65.