Microcosm_ E. Coli and the New Science of Life - Carl Zimmer [111]
Lederberg’s efforts ultimately led to an agreement between the United States and the Soviet Union on standards for sterilizing spacecraft. Yet Lederberg became famous not for his worries about contaminating other planets but for his worries about the return trip. If life did exist on other worlds, a spacecraft coming back to Earth might accidentally carry some of it home. Alien microbes might wreak havoc on our planet. They might cause a global plague or trigger a famine by attacking crops.
“The fate of mankind could be at stake,” Lederberg warned. Soon reporters were describing the dire warnings of the Nobel Prize–winning biologist, using headlines such as “Invasion from Mars? Microbes!” A version of Lederberg even ended up in the 1971 science-fiction movie The Andromeda Strain: the intrepid biologist desperately trying to find a cure for a virus from outer space.
For all his worries, however, Lederberg did not want to seal off the sky. At NASA’s invitation, he set up a laboratory at Stanford University to begin building a device that could detect signs of life on another planet. In some ways the work was mundane. Lederberg and his colleagues tinkered with conveyor belts and mass spectrometers. But they also faced a profound question, less scientific than philosophical: How can you search for life you’ve never seen? The question, Lederberg decided, required a new branch of biology all its own. He dubbed it exobiology, the biology of life beyond Earth.
The goal of exobiology was to discover whether life has begun more than once in the universe and whether it has taken more than one form. Does life have to use DNA? Does it have to build its cells from protein? Is there something about these molecules that suits them to life, something no other combination of atoms can possibly have? “These questions might be answered in two ways,” Lederberg wrote. “Presumptuous man might mimic primitive life by imitating Nature, furnishing substitute compounds. More humbly, he might ask Nature the outcome of its own experiments at life, as they might be manifest on other globes in the solar system.”
Looking for unearthly forms of life would be difficult because scientists could not predict what they might find. Lederberg felt content starting off with a more conventional search. “We can defer our concern for such exotic biological systems until we have got full value from our searches for the more familiar,” he wrote.
NASA agreed. The agency would search for the familiar, and it would search for it on Mars. Mars was just enough like Earth to offer some hope of harboring life. In 1965, Mariner 4 became the first probe to send back detailed pictures of the surface of Mars. It revealed a bleak landscape, pocked with craters and devoid of forests and other signs of life. If life did exist on Mars, it probably just consisted of microbes. NASA used the pictures from Mariner 4 and later probes to design a mission to land a probe on the surface of Mars. On July 20, 1976, nineteen years after Lederberg watched the first satellite rise from Earth, Viking 1 became the first probe to land on another planet.
Sadly, the mission was generally agreed to be a bust. Viking 1 found no signs of organisms that could convert carbon dioxide to organic carbon. Some kinds of terrestrial life, such as E. coli, consume organic carbon and release carbon dioxide as waste, but Viking found no trace of this metabolism either. One last experiment remained, a final court of appeals. Viking scooped up soil, heated it up to liberate molecules, and then fired them down a tube, where they could be measured. The probe could detect no organic carbon in the Martian soil whatsoever. This result was devastating, because life has created huge amounts of organic carbon on Earth, not just in the bodies of living things but in the waste they leave behind.
“That’s the ball game,” said Gerald Soffen, the