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How Carl Sagan Worked

        Science | Physicists

The famous scientist and popularizer of science poses in his Cornell lab circa 1974, turtleneck sweater and all.
The famous scientist and popularizer of science poses in his Cornell lab circa 1974, turtleneck sweater and all.
Santi Visalli Inc./Getty Images

Resting on the foreign, reddish surface of Mars, a compartment in NASA's Phoenix spacecraft carries a heartfelt message from one of the world's most fascinating researchers. It reads:

"Whatever the reason you're on Mars, I'm glad you're here, and I wish I was with you."

Crafting that message, one of a collection of DVD dispatches intended for future Mars settlers, was just another day for Carl Sagan. Did anyone delight in describing the universe, with its billions of galaxies, as much as Sagan? Who else would launch a record with Bach and Mozart into space?

His yearning to understand the cosmos wasn't limited to the expansive blackness beyond Earth's atmosphere. He believed everyone should share in the wonders of science and the universe -- a legacy that lives on through colleagues, fans and family to this day. Some present-day admirers mix Sagan's musings in music form ("A Glorious Dawn," anyone?). Humbly, Sagan reminded us that we too are made of "star stuff."

Perhaps the phrase "billions upon billions of stars" conjures up breath-taking images from the PBS series "Cosmos." Or you may be familiar with Sagan's skeptical attitude or search for extraterrestrial life. He also left his mark on political and religious discussions, recognizing that science affects many facets of life. Yet one Sagan biographer notes that the greatest dichotomy of Sagan's life was Sagan himself -- he was both prophet and skeptic; someone who teetered between being uplifted by creativity and grounded by the facts [source: Davidson].

Let's get to know the man whose idea of fun entailed characterizing the mysterious surfaces of planets, describing the chemistry required for life and pondering humans' place in the enormous universe. His legacy spans the space program, academia and popular media, and it all began in Brooklyn.

The Birth of a Star

Born to a Jewish-Ukrainian family in Brooklyn, New York, Sagan was the son of hardworking parents who did their best to give him opportunities and protect him from the grim realities of the Holocaust, which negatively affected extended family abroad. Sagan's mother had particularly high aspirations for her son. Some say her desire for Sagan's success was to make up for opportunities she lacked in life [source: Davidson].

Thoughts of unseen worlds starting taking root in Sagan when the World's Fair set up in New York in 1939. As a young boy, he became intrigued by exhibits touting the role of science and technology in humanity's future. The displays hosted model skyscrapers and cities; booths enticed him with the new invention of the television. Sagan delighted in the future's potential -- it would be ripe with technology and science [source: Poundstone].

His inspirations drove him toward answering fundamental questions about the natural world -- a behavior routinely satisfied with his very own children's library card. Museums enraptured young Sagan, offering glimpses of other parts of the world and the exotic [source: Davidson].

Sagan received his bachelor's and master's degree in physics, and a doctorate in astronomy from the University of Chicago, all while he was still in his 20s. After that, he did a stint at the Smithsonian Astrophysical Observatory and taught at Harvard University. He soon found a position at Cornell University in Ithaca, N.Y., where he settled into a more permanent position as a professor and director of the Laboratory for Planetary Studies.

During and after his studies, Sagan worked with NASA, advising the agency on several space projects, including the Apollo, Voyager, Viking, Pioneer, Mariner and Galileo missions.

But Sagan didn't peak as a science star until he began working on the educational PBS show "Cosmos." Sagan's books and essays also catered to the masses, granting him numerous awards, including the prestigious Pulitzer Prize for his book "Dragons of Eden."

Sagan first wed biologist Lynn Margulis in 1957; then, artist Linda Salzman in 1968; and finally author Ann Druyan in 1981. He was the father to five children, but his commitment to work sometimes took a toll on providing a normal family life [source: Poundstone].

What's in a Planet?

Get to know Earth's spirited sister planet Venus in this video.
Science Channel

Like most astronomers, Carl Sagan relied on indirect measurements of faraway planets and galaxies for his research. Years later, even as more precise tools have emerged, his work on planetary atmospheres remains relevant. His passion also led to him creating the Planetary Society.

Take his description of Venus's atmosphere, for example. In the early 1960s, Sagan tackled why the second planet in our solar system trapped heat in its atmosphere. He hypothesized that a greenhouse effect kept Venus at a toasty 900 degrees Fahrenheit (500 degrees Celsius). As sunlight hits the surface of the planet, gases in its atmosphere trap the heat rather than let it escape. Sagan's conclusions opened the door to discovering a similar phenomenon on other planets -- even Earth.

By studying other planets' atmospheres and chemical cycles, Sagan discovered that many of the same processes were at play on our home planet. Despite Earth's early, icy history, geology shows that not all water was bound up in ice. But what propelled the planet to the warmer, wetter place it is today? That's what puzzled Sagan and his colleague George Mullen, who labeled the issue the faint young sun paradox in 1972. Since stars gain energy and luminosity as they age, the sun emitted more and more energy that could have helped Earth thaw. Yet Sagan and Mullen suggested that an increasingly powerful sun couldn't have been entirely responsible for melting young Earth; rather, other greenhouse gas cycles may have accelerated warming. Scientists are still trying to piece together the puzzle today, but Sagan helped draw attention to the paradox.

Mars enchanted Sagan, too, driving his strong desire to explore the red planet. He hammered out the logistics of space missions at the NASA Jet Propulsion Laboratory and described Mars' seasons, citing the planet's seasonal storms as causes behind its shifting features.

The famous astronomer also believed there was more to Saturn's moon Titan than meets the telescoped eye. He hypothesized that complex organic molecules lent a reddish hue to the distant moon, which ended up being true.

In Pursuit of (Other) Life

Are we really alone in the universe? Can physics and math -- fundamental truths that underpin the universe -- act as symbolic messages to communicate with other life?

Carl Sagan wondered similar questions. Perhaps more than anyone, Sagan wanted to find other intelligence in the universe, but he was grounded by the lack of proof [source: Poundstone]. He famously coined the phrase, "Extraordinary claims require extraordinary proof," and at times dismissed his own sci-fi fantasies of aliens lurking around the cosmic corner. In a sense, Sagan's obsession with finding other life made him more relatable to the public. At the time, it was rare to see scientists comment on such things.

His 1985 novel "Contact," which was later made into a motion picture, portrayed one scientist's transmitting signals into space with the hope of intercepting other life. The novel certainly drew inspiration from Sagan's search for ET at the SETI Institute and from colleague Jill Tarter in particular. Sagan also strove to understand the chemical recipe necessary for basic life outside of Earth to take root, a discipline known as exobiology. He promoted using biology, chemistry and physics to probe life's origins.

But his most memorable space projects were less about hard science and more about humanity and love.

Should ET ever intercept a NASA spacecraft, Sagan wanted to be ready. This explains the golden record on Voyager 1 and 2, each containing "sounds" from the natural world and cultures, and 115 "images" representative of the diversity of life on Earth [source: NASA Jet Propulsion Laboratory].

"His feeling was that the American taxpayers and the world are really helping to support this, so we should have something that they can relate to," said Sagan biographer William Poundstone. The golden record united people despite their myriad differences.

Sagan's wife, Ann Druyan, recalls creating her own sounds for the project by recording and translating her body's brainwaves and vital signs into music. During the recording, she meditated and told the story of the universe (as humans knew it) with her thoughts. Her mind wandered to her love for Sagan, too. With the spacecraft now venturing deeper into the unknown of interstellar space each moment, Druyan still views her recordings as a romantic, cosmic tribute to the relationship she and Sagan shared [source: Druyan].

Millions Upon Millions ... Watched Him

If reading this article has made you want to listen to Sagan waxing poetic about the cosmos, then watch these videos. We think he tackles the big bang with aplomb.
Science Channel

Sagan soon appeared more often on people's TV sets than in academic journals. After premiering in the 1980 PBS series "Cosmos: A Personal Voyage," he rose to the zenith of popular science communicators (think Stephen Hawking and Neil deGrasse Tyson). The studio became his new lab, as he gradually decreased his work in academia.

In "Cosmos," Sagan promoted viewers' interest in science by taking them along for an intergalactic journey through the universe. His entrancing voice reached millions of people worldwide across languages and cultures (not "billions upon billions," as he's teased for saying).

Not everyone praised Sagan as science's champion, though. Many scientists valued Sagan's efforts to popularize science, but some thought he was too big of a media star. When journalists and media outlets needed an expert opinion, they often went to Sagan because of his willingness to help. This sometimes overshadowed other researchers' public visibility and inflated Sagan's actual involvement [source: Poundstone].

Ann Druyan, Sagan's wife, says her husband wanted everyone to have access to the scientific knowledge usually locked away in the minds of experts. Sagan also credited the science-fiction genre as sparking people's love for scientific exploration and discovery. Sagan described science and science fiction interweaved in a "dance" of sorts, taking turns inspiring each other. In his audio message to Mars, he says sci-fi spurred young people to learn more about Mars -- a trend that might help humanity get there someday [source: The Planetary Society]. Sagan also shared success as a popular science writer.

But what made Sagan unique was his knack for straddling various disciplines. As scientific fields become more specialized, generalists like Sagan are now a rarity. Biographer William Poundstone described Sagan as a person who fired on multiple cylinders, meshing several realms of science into his public messages.

Beyond the Cosmos

Carl Sagan's worldview spanned beyond the cosmos and its scientific glory. In fact, many view him as a leader of the skeptic movement and famous critical thinker.

Sagan made popular "the idea that really you can use scientific-type reasoning in all sorts of walks of life," says William Poundstone, who wrote a biography on Sagan. "Everything from politics to health, to the actual beliefs and superstitions that we all have." It's something he's admired for.

The famous scientist and author was particularly outspoken about the nuclear arms race and Cold War between the United States and the Soviet Union. Sagan lobbied to reduce nuclear arms and warned of the potential dangers humanity could bring upon itself. His nuclear winter theory gained public attention and grew out of his earlier planetary science studies. He speculated that a barrage of nuclear explosions would churn up so much dust that it would interfere with the Earth's climate. People surviving the explosions would be doomed if enough dust blocked the sunlight needed to grow crops. Sagan's scenario may hold some truth, but it also has its critics [source: Poundstone]. Either way, Sagan highlighted the fact that there could be unintended consequences from nuclear war.

Ann Druyan, Sagan's wife, describes him as a "scientist through and through." Sagan's religious views stemmed from his emphasis on evidence and truth -- two pursuits that ruled out traditional worldviews of God to him. Contrary to other labels, Druyan says Sagan identified himself as agnostic, not atheist -- he didn't believe in religions and tried to not belittle them. But this didn't mean he wasn't a spiritual person, she said.

After being diagnosed with a rare bone marrow disease in 1994, Sagan weighed his options and sought the best treatment in Seattle, Wash. Treatment would likely involve a bone marrow transplant -- Sagan's sister, whom he was never too close with, volunteered to partake in the procedure [source: Poundstone].

But Sagan didn't get entirely better. More than a year and a half after the transplant, he became sick from an infection. On Dec. 20 1996, Sagan, then 64, succumbed to his illness.

Druyan says Sagan's legacy lives on. Shortly following his death, she and others help finish the movie based on his book "Contact." It was bittersweet, she said.

At the end of the film, "For Carl" appears on the screen.

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More Great Links


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  • Anderson, Charlene. "Projects: Observing Earth. Carl Sagan on Venus and Mars." (Feb. 1, 2012)
  • Brazell, Karen. "Happy Belated Birthday, Carl!" PBS. Nov. 10, 2010. (Feb. 7, 2012)
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  • Turco, R.P., Toon, O.B., Ackerman, T.P., Pollack, J.B., & Sagan, Carl. "Nuclear Winter: Global Consequences of Multiple Nuclear Explosions." Science. Vol. 222, no. 4630. 1983. (Feb. 1, 2012) Environmental Protection Agency. "Carbon dioxide." April 15, 2011. (Feb. 1, 2012)