The Search for Life Elsewhere Begins with Defining Life
To search for life elsewhere in the solar system and the universe beyond, one must first define “life.” That was the message of a day-long celebration of 50 years of NASA research in exobiology and astrobiology on Thursday.
Molecular biologist Steve Benner explained to the audience that one can develop a “laundry list” of criteria that must be met for something to be described as life, but any such list necessarily rests on the biases of the person creating it — a carbon-based life form that needs water to survive. What about life forms that might be based on other elements, like silicon? Benner was a member of a National Research Council study committee that published a report entitled Limits of Organic Life in Planetary Systems, dubbed the “Weird Life” report, which ruminated scientifically on other types of life forms that might exist.
Such questions are not only for Star Trek fans, but for researchers who are actively engaged in searching for life on other planets and their moons in our solar system and beyond. In this case “life” is just that, life, not necessarily intelligent life, which is the focus of the Search for Extraterrestrial Intelligence (SETI), a more controversial undertaking. As recounted by former NASA Administrator Dan Goldin in a rare talk about the space program since he left NASA in 2001, NASA has not directly supported SETI since 1993 when the Senate led the effort to cancel NASA’s involvement in the program. Since then, SETI has relied on private sponsorship.
NASA, however, is fully engaged in the search for life in earlier stages. Since the life forms we know do require water for survival, “follow the water” became the theme for NASA’s planetary exploration program while Goldin was Administrator. Although Benner and others want a more expansive view of what life might be, the reality is that one can only search for what one knows.
James Lovelock of Oxford University, founder of the Gaia hypothesis, reminisced about joining NASA in the early 1960s and being given the task of designing a method to determine if there is life on Mars in four days, which he did — by studying the atmosphere. A decade later he published a book outlining a hypothesis he called Gaia, after the Greek goddess of Earth, that argues that life on Earth is part of a self-regulating system – essentially the planet and all the life on it function as a single organism. The somewhat controversial idea is that life on Earth developed and continues to exist not just because of luck, but because the physical, chemical and biological systems of Earth work together to regulate the planet to maintain that life. Some scientists refer to a “Goldilocks” zone around a star where temperatures are not too hot, not too cold, but just right for life to develop. Lovelock calls that “ridiculous,” insisting that Earth is not within what scientists would consider the Goldilocks zone for our Sun, yet it is teeming with life because of the interaction of the atmosphere and everything else on the planet.
Lynn Margulis of the University of Massachusetts, one of the primary proponents of the Gaia hypothesis — or theory, depending on one’s viewpoint — blamed neo-Darwinists for attacking it and explained that it takes time for people to accept a new way of thinking. Quoting Emily Dickinson, she told the audience that “The truth must dazzle gradually or every man be blind.”
The seminar was information- and intellectually-rich. Topics included historical accounts of NASA’s Viking program, the first designed specifically to find life on Mars, and of the ups and downs of astrobiology at NASA, which dipped when people misinterpreted Viking’s findings as proof that there was no life anywhere on Mars, but resurged after the 1996 “Martian meteorite” discovery.
Cultural perspectives on the implications of finding life elsewhere — or not finding it, which would be equally significant — were discussed in a panel that included journalist Marc Kaufman of the Washington Post. He is writing a book on astrobiology and said that in his travels around the world doing research for it he found that people everywhere were fascinated by the search for life. A story he wrote for the Post on the discovery of a planet in the habitable zone of another star was the most read and emailed story on the Post’s website for several days and shared on Facebook more than 7,500 times. Other members of that panel emphasized the need to consider religion and science together when communicating with the public since astrobiology is based on the theory of evolution. Connie Bertka of the Carnegie Institution pointed out that 42% of the U.S. population does not accept evolution and that number has been unchanged for 50 years.
But the question that kept returning throughout the day is “What is life?” Nobelist Baruch Bloomberg, who was the first director of NASA’s Astrobiology Institute, argued that it is not that we are searching for life, we are testing the hypothesis that there is life elsewhere and searching for the data to prove the hypothesis. “How do you know if something’s alive,” he mused. “We have characteristics and if enough of them are satisfied then people say ‘that’s life.’ It is hard to know how much data you need, but when it happens, you know it.”