(From Scientific American Magazine)

Carl Sagan

A Pale Blue Planet Mourns the Passing of a
Passionate Scientist

Please visit www.carlsagan.com

The death of Carl Sagan on December 20, 1996, robbed the science world of one of its most creative researchers and articulate spokesmen. At the time of his death, Sagan was David Duncan Professor of Astronomy and Space Sciences and director of the Laboratory for Planetary Studies at Cornell University, where he had held a professorship since 1971.

Sagan was an avid proponent of space exploration who contributed to most of the unmanned missions that explored our solar system. These included the Mariner 9 spacecraft, which produced the first detailed images showing that Mars is currently a desolate, cratered world; the Viking orbiters and landers, which searched (unsuccessfully) for life on the surface of the Red Planet; the Pioneer and Voyager probes that provided the first surveys of the outer planets and their moons; and the Galileo craft, which is currently sending back extremely detailed images of Jupiter and its giant satellites.

Sagan's work transformed our understanding of Earth's place in the cosmos. He helped to determine that the surface of Venus--once considered a possibly hospitable place--is hellishly hot, fried by a greenhouse effect run amok. Yet he also showed that the universe abounds with intricate, carbon-based chemicals that could be the precursors of other living things. And Sagan collected evidence that Saturn's moon Titan has an atmosphere containing organic molecules similar to the building blocks of life. That work was stunningly confirmed by Voyagers 1 and 2 in the 1980s.

Throughout his career, Sagan argued for the importance of searching for signs of extraterrestrial life. At Cornell, he pioneered the new field of exobiology--the study of possible alien biochemistry and life forms. He conceived a message plaque, containing a greeting from the people of Earth, which adorns the Pioneer 10 spacecraft, now headed into interstellar space (a more sophisticated, engraved phonograph record adorned the two Voyager craft, also on their way to the stars). Along with various collaborators, including Paul Horowitz of Harvard University, Sagan supported projects that use radio telescopes to listen for signals from possible intelligent alien civilizations.

But perhaps Sagan's greatest skill was his ability to communicate with individuals here on Earth. Through a series of books, magazine articles and television shows, he reached beyond the scientific community to convey the excitement of his research to the lay public. (His writing graced the pages of Scientific American; three of his articles are available from this page.) Sagan's concerns ranged far and wide, from the effects of nuclear war to the evolution of the mind to the intellectual erosion brought about by pseudoscience (the subject of his most recent book, The Demon-Haunted World). His television series Cosmos reached an estimated audience of 500 million people; his novel Contact is being made into a movie that will be released later this year. Sagan also co-founded the Planetary Society, the largest space-interest group in the world.

My own interaction with Carl Sagan began on the printed page, when I read his electrifying first book, The Cosmic Connection, published in 1973. Sagan's prose was utterly unlike the rote descriptions of the planets (complete with tables listing mass, density, period of rotation and so on) that I had read in various astronomy books for young readers. In a chapter entitled "The Moons of Barsoom," he weaves together the science-fiction lore of Edgar Rice Burroughs with his on-the-scene descriptions of Mariner 9's first images of Mars's two tiny satellites, Phobos and Deimos. These enigmatic lumps of rock, the subject of years of curious speculation, turned out to resemble horribly pockmarked potatoes. They are so tiny, Sagan explains, that an astronaut standing on their surfaces could easily pitch a baseball into orbit (Phobos, the larger of the two, is just 14 kilometers in its longest dimension). What an image to a curious youth--baseball on the moons of Mars!

In another chapter, Sagan speculates on the likelihood that other planetary systems contain worlds that support life. He includes an illustration depicting five "model solar systems" created by a computer simulation designed by Stephen Dole, then at Rand Corporation. I could not pry my eyes from those simple, schematic drawings. Again and again, I tried to visualize what those imaginary worlds would look like, to choose which of these planets might have breathable atmospheres and balmy temperatures. The rapid discovery of planets around sunlike stars, starting late in 1995, offered the first example of what other planetary systems look like. That these systems exist at all affirms Sagan's belief that planets are commonplace throughout our galaxy; that they look immensely unlike the ones created by Dole's model underscores how greatly the creativity of Nature outstrips that of the human imagination. I am glad that Sagan lived to witness these stunning detections.

Later, as an editor at Scientific American, I had various occasions to meet Sagan, even to work with him. I was amazed that, despite the tremendous energies he devoted to his popular writing and teaching, he continued to be an active researcher as well. He never lost enthusiasm for his investigations into the remarkable prevalence of organic chemicals or for his quest for signals from alien civilizations. It did not matter that such signals have not yet been found; Sagan delighted in grasping at tasks and concepts that lie far beyond the grasp of science. In that vein, the final chapters of The Cosmic Connection contain his reflections on what extraterrestrial intelligences might be like and how they might communicate. Sagan's words are both inspiring and humbling:

"We are like the inhabitants of an isolated valley in New Guinea who communicate with societies in neighboring valleys (quite different societies, I might add) by runner and by drum. When asked how a very advanced society will communicate, they might guess by an extremely rapid runner or by an improbably large drum. They might not guess a technology beyond their ken. And yet, all the while, a vast international cable and radio traffic passes over them, around them, and through them...

"We will listen for the interstellar drums, but we will miss the interstellar cables. We are likely to receive our first messages from the drummers of the neighboring galactic valleys--from civilizations only somewhat in our future. The civilizations vastly more advanced than we, will be, for a long time, remote both in distance and in accessibility. At a future time of vigorous interstellar radio traffic, the very advanced civilizations may be, for us, still insubstantial legends."

--Corey S. Powell, staff writer