|Early Planet X - Pluto|
Miller’s landmark work, carried out in 1953, meant that scientists could study the origins of life in a laboratory setting. Urey and Miller were interested in terrestrial life, but others soon explored the cosmic implications of their work. Life might appear in other regions of the universe where Earthlike conditions prevailed. It was no longer an exclusively terrestrial phenomenon. Carl Sagan started graduate work at the University of Chicago in the midst of these new developments on the origins of terrestrial and extraterrestrial life. Sagan’s mentor at Chicago was the astronomer Gerard Kuiper. While completing his doctoral studies with Kuiper, Sagan met the Nobel laureate geneticist Joshua Lederberg (1925–). The two men were brought together by their common interest in the origins of terrestrial life and the possibility of extraterrestrial life. Lederberg was a pioneer in the scientific study of extraterrestrial life. In 1960 he named the new science exobiology and used his considerable scientific reputation to enhance its credibility. Lederberg hoped that exobiology would give America’s space program a new focus. Instead of concentrating upon missiles and manned flight, the program would turn to scientific topics. From its beginnings, exobiology was a highly speculative and controversial field of study. Despite its uncertain status among scientists, exobiology found a home within the space sciences. NASA created an Office of Life Sciences in 1960, sponsored conferences on extraterrestrial life, and funded exobiological research. Upon Lederberg’s recommendation, Carl Sagan was asked to serve on a number of government panels and commissions that advised NASA on matters relating to space exploration and biology. Sagan worked with NASA during the directorship of James C. Fletcher. Fletcher was a very able administrator, a tireless advocate for space exploration, and a supporter of the search for extraterrestrial life. He was also a devout Mormon whose religion had long taught that inhabited worlds existed outside our solar system. For these varied reasons, Fletcher brought the Viking Mars missions to a successful completion and encouraged NASA-sponsored efforts to communicate with intelligent beings outside the solar system.
|Viking images of Mars|
Joshua Lederberg’s and Carl Sagan’s strong belief in the existence of extraterrestrial life found favor in some NASA circles, but it was disputed by officials and scientists preparing for the Apollo flights to the Moon from 1969 to 1972. The central issue of the dispute, microbial contamination, pitted exobiologists against geologists and engineers at the space agency. The exobiologists warned that terrestrial microbes carried to the Moon by Apollo spacecraft and astronauts could endanger lunar life forms. Likewise, lunar microbes accidentally brought back from the Moon might infect inhabitants of the Earth. Sagan urged the sterilization of all spacecraft traveling to the Moon. NASA officials ruled out sterilization of the Apollo lunar landers. It would have been very difficult, if not impossible, to place a sterile lander on the Moon. In order to protect humans from infection by lunar microbes, NASA agreed to quarantine returning Apollo astronauts and their cargo of lunar rocks. Appropriate tests made on the first astronaut team to visit the Moon showed no evidence of lunar life. NASA dropped the quarantine of returning astronauts after several more lunar missions. By 1972, when Apollo 16 flew to the Moon, virtually all scientists agreed that the Moon was lifeless. Carl Sagan was one of the few to dispute this conclusion. He maintained that microorganisms might live deep beneath the lunar surface. In the early 1970s, Sagan became a member of NASA’s imaging teams for Mariner 9 and the two Viking missions. The imaging team interpreted the pictures of the Martian surface recorded by the spacecraft’s electronic cameras. Sagan was the sole astronomer, and the only scientist with an extensive background in biology, on the team. Furthermore, he was a staunch believer in the existence of advanced Martian life at a time when most scientists considered it doubtful that microbes existed on the planet. One of his NASA colleagues explained Sagan’s position in these words: “Sagan struggles to create situations where life might exist. It’s a compulsion.”