Extraterrestrial Civilizations

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Extraterrestrial Civilizations
Extraterrestrial Civilizations - bookcover.jpg
Hardcover edition
Author Isaac Asimov
Country United States
Language English
Subject Extraterrestrial life
Publisher Crown
Publication date
Media type Print (Hardcover and Paperback)
Pages 282
ISBN 978-0-517-53075-7
OCLC 4638134
LC Class QB54 .A84 1979

Extraterrestrial Civilizations is a 1979 book by Isaac Asimov, in which Asimov estimates the probability of there being intelligent extraterrestrial civilizations within the Milky Way galaxy. This estimation is approached by progressively analyzing the requirements for life to exist.


The term "Earth-like world" is prominent, in that the assumption is made that any world where life could evolve would have certain similarities to Earth, such as temperature ranges and gravity sufficient for an atmosphere to exist. Asimov begins with the estimated number of stars in the galaxy, 300 billion.[1]

This number is then reduced to 280 billion as stars without planetary systems are discarded, and then furthermore reduced as more factors are taken into consideration. This process culminates in the statement that "the number of planets in our galaxy on which a technological civilization is now in being is roughly 530,000."[2]

See also[edit]


  1. ^ J. H. Jenkins. Review of Extraterrestrial Civilizations at the Wayback Machine (archived April 5, 2008)
  2. ^ The Internet Book Database of Fiction. Extraterrestrial Civilizations