What Are the Odds of Life on Another Planet?

What are the odds of life on another planet? First, it depends on what kind of life you’re talking about. There’s a great deal of biodiversity on the Earth itself, from the simplest life, to the most complex, human life. Life here on Earth is incredibly inventive and remarkably resilient. It has emerged from an intricate process, tempered by natural selection, over a span of billions of years. This long and complex process, has given rise to the survival of a plethora of species on the one hand, and the extinction of a much larger number of less fortunate ones on the other. Life on Earth is resilient, its branches changing over time, adapting to the most disparate, transient and extreme of circumstances.

Life on Another Planet: The Growing Search

Inquiry about the possibility of the existence of extraterrestrial life is generally concerned with an interest in life that is similar to that which has emerged on Earth, particularly life found at the more complex end of the spectrum. While the existence of life within our solar system on other planets such as Venus, Mars and the gas giants, either in the present or at some point in the past, remains conceivable, the search has expanded to include extrasolar planets.

Image: Artist's rendition of Kepler 69c, habitable planet

NASA’s Kepler Mission: The Search for Habitable Planets

NASA’s Kepler Mission is aimed at carrying out a search for “habitable planets.” The Kepler Mission Quick Guide explains that the Mission “is specifically designed to survey a portion of our region of the Milky Way galaxy to discover dozens of Earth-size planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets.”

Earth-like Planets Around Sun-like Stars

What is “the habitable zone”? Also known as “the Goldilocks zone,” the habitable zone is the area around a star that is neither too hot nor too cold to permit the presence of liquid water on a planet’s surface. Because water has been essential to life on Earth, planets in the habitable zone would be most likely to provide the type of environment that could facilitate the development and survival of extraterrestrial life similar to life found on Earth. In other words, if we are looking for life similar to the life found on Earth, then planets that are themselves similar to Earth, going around Sun-like stars would be logical places to focus our search.

The Kepler spacecraft has identified 3,538 planet candidates. Scientists working with the data collected from the spacecraft “have statistically determined that twenty percent of Sunlike stars in our galaxy have Earth-sized planets that could host life.” In other words, 1 in 5 of the Sun-like stars in the Milky Way galaxy have habitable planets, that’s at least 8.8 billion. Study co-author, Geoff Marcy of the University of California at Berkeley commented to the Associated Press that this statistical analysis of the data means that

“just in our Milky Way galaxy alone, that’s 8.8 billion throws of the biological dice.”

Up-to-date information on the progress of analysis of the data collected from the Kepler mission can be found on NASA’s Kepler Mission page.

The Drake Equation: Calculating the Odds of Intelligent Extraterrestrial Life

One of the most well-known attempts to calculate the odds of the existence of intelligent life on another planet is found in an equation developed by radio astronomer, Dr. Frank Drake. The equation, known as the Drake Equation, lays out factors that are thought to play a vital part in the development of technological civilizations, where N is defined as “the number of civilizations in the Milky Way Galaxy whose electromagnetic emissions are detectable.” While there is no official solution to the equation, scientists regard it as a useful tool for exploring the role of each of the factors identified by the equation and the possibility of detecting an alien transmission.

The SETI Institute: Listening for Alien Contact

The SETI Institute (short for the Search for ExtraTerrestrial Intelligence) is aimed at detecting communication attempts carried out by extraterrestrial life forms, intelligent enough to engage in such interstellar communication in the first place. According to the SETI website, “the mission of the SETI Institute is to explore, understand and explain the origin, nature and prevalence of life in the universe. Alien life has not been detected yet, however, the search continues as researchers continue to collect and analyze incoming data. Want to get involved? The SETI Institute has a membership program called TeamSETI. Learn more at www.seti.org. To stay informed about the SETI search visit, http://setiquest.info and try out their online human-powered search at http://www.setilive.org.


Borenstein, Seth. “STUDY: 8.8 BILLION EARTH-SIZE, JUST-RIGHT PLANETS.” The Big Story. The Associated Press, 4 Nov. 2013. Web. 11 Nov. 2013. <http://bigstory.ap.org/article/study-88-billion-earth-sized-just-right-planets>.

“Drake Equation.” SETI Institute. N.p., n.d. Web. 11 Nov. 2013. <http://www.seti.org/drakeequation>.

Keck Observatory. ” Odds are on oodles of Earths.” PlanetQuest. JPL, 4 Nov. 2013. Web. 11 Nov. 2013. <http://planetquest.jpl.nasa.gov/news/139>.

“Kepler: About the Mission.” Kepler: About the Mission. NASA, n.d. Web. 10 Nov. 2013. <http://kepler.nasa.gov/Mission/QuickGuide/>.

“Kepler: Home Page.” NASA.gov. N.p., n.d. Web. 11 Nov. 2013. <http://kepler.nasa.gov/>.

Image Credit: NASA

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