Jewish-American astronomer and physicist Carl Sagan was known for both his popularizing of science and addressing social issues with an evolutionary awareness. Born in Brooklyn, New York, Carl Sagan was one of two children born to Sam Sagan and Rachel (Gruber) Sagan. Considered to be an intelligent and inquisitive child, his interest in science began at an early age due to the ever-growing popularity of science fiction as well as advancements in technology. Graduated from Rahway High School (1951), Sagan entered the “Hutchins Program” at the University of Chicago, where he received his BA in 1954 and 1955 (general and physics) and MA (physics) in 1956. Sagan continued his education at the University of California, Berkeley and received a PhD (astronomy/astrophysics) in 1960.
Considered an inspirational teacher, Sagan taught at both Harvard University (1962-1968) and Cornell University where he was director of the Laboratory of Planetary Studies. Yet his major contributions were in research and writing, such as his insights into atmospheric conditions on the planet Venus and planetary conditions on Mars in relation to the possibility of extraterrestrial evolution elsewhere in the universe. Working on various government projects, he was well known for his contributions to the Galileo and Pioneer X and interpretative results of the Mariner unmanned space probes. Further inquiry into extraterrestrial life continued by SETI (originally Project OZMA) established Sagan as a prominent scientific figure and reaffirmed his own speculation into the existence and duration of extraterrestrial life. However, it was Sagan’s ability to convey technical scientific information and stimulate the public’s imagination that made him famous. Sagan was best known for his PBS series Cosmos (1980) and his novel Contact (1985), which was later adapted for film by Robert Zemeckis (1997). Sagan also received many awards and medals for his academic, public, and literary contributions.
Sagan’s academic achievements and theoretical development were directly or indirectly influenced by H. J. Muller, Harold Clayton Urey, Stanley Miller, Joshua Lederberg, Gerald Kuiper, and Jim Pollack. His theoretical orientation was driven by hopeful speculation about the evolution of extraterrestrial life. To these ends, Sagan had directed his scientific inquiries toward the theoretical precursors of life on this planet and other planets in the universe. Consequently, atmospheric and general conditions became a point of scientific speculation. Due to proximity, and perhaps influenced by the romanticism of science fiction, the planets Venus and Mars became targets in the quest for planetary knowledge and possible confirmation of extraterrestrial life. Drawing upon the popularized “greenhouse effect” on our planet, Sagan applied this principle to the conditions on Venus. According to Sagan, Venus’s greenhouse effect was due to a combination of carbon dioxide and water vapor (Sagan’s addition) that would serve to retain inferred radiation. Though high surface temperatures were speculated, Sagan speculated that Venus’s planetary rotation could possibly hold temperatures to a point that may support life, for example, similar to life found in extreme temperatures at thermal vents. The information sent by Mariner II confirmed Sagan’s belief that intense radiation contributed to Venus’s temperature (green-house effect). However, Venus’s surface temperature was greater than expected; consequently, it appears impossible for Venus to support life.
Turning to the planet Mars, Sagan speculated that life, albeit microbial, may exist. However, the preliminary photos taken by Mariner IV did not expose any overt expressions of life. He then speculated on two key Martian features: the “canals” and the “wave of darkening” that are observable. As a plausible explanation, Sagan hypothesized two points concerning these features: the “canals” were a product of plate tectonics and the “wave of darkening” is a product of raging turbulent dust storms. Although the explanation for the appearance of “canals” was proven false, the explanation of dust storms retained its viability. However, as science advanced, the possibility of simple or advanced extraterrestrial life on Mars was negated by both Viking and more recent expeditions.
Influenced by both scientific method and Darwinian evolution, Sagan rejected religious or traditional cosmologies in favor of a rational and scientific explanation. In this critical process, he fought and exposed the pseudoscience that is often promoted and accepted without critical analysis. From the annals of theoretical space exploration and the duration of technological life in the universe (known as the “value L”), Sagan turned his attention to problems that face our species on this planet. He opposed militarism and the nuclear buildup of the Cold War, mostly contributing to the debates on SDI and the reality behind a nuclear winter. Promoting peace, democracy, and education, Sagan continued to endorse an optimistic view in an otherwise nihilistic reality of planetary extinction.
Implementing whimsical and catchy phrases like the Baloney Detection Kit, Sagan encouraged readers to apply skepticism and logic in the evaluation of any expressed ideas—religious, political, and scientific. As a secular humanist, evolutionist, and materialist, Sagan knew the perils that ultimately face an individual. Even during his life-ending battle with complications from myelodysplasia, Sagan continued to enlighten and promote the peaceful unity of our species. Perhaps it was his understanding of the true nature and implications of evolution in the cosmos that contributed to his relentless and productive quest for extraterrestrial life.
- Davidson, K. (1999). Carl Sagan: A life. New York:
- John Wiley & Son. Sagan, C. (1980). Cosmos. New York: Random House.
- Sagan, C. (1997). Billions and billions: Thoughts on life and death at the brink of the millennium. New York: Random House.