NASA astrobiologist Stephen Freeland offered three “clues” to the possibility of extraterrestrial life at a June 19 discussion hosted by the AAAS Dialogue on Science, Ethics, & Religion.
Exponential growth in the discovery of extra-solar planets has raised “big questions” about our own cosmic significance, said Freeland, researcher with the NASA Astrobiology Institute and Director of Interdisciplinary Studies, University of Maryland Baltimore County.
“Are we alone? If we’re not alone, would other life look like us? These questions go way beyond science,” he said at the Exoplanets and Life Beyond Earth event. Even so, some researchers are pursuing answers to such questions, which relate to the mystery of the “n=1 challenge”—the fact that life has so far been identified only on Earth.
The first extrasolar planet, or exoplanet, was confirmed around a normal star in 1995, Freeland said. Less than 20 years later, nearly 1000 planetary systems have been confirmed and thousands more are under consideration as likely candidates, said Jennifer Wiseman, DoSER program director and NASA astrophysicist /senior project scientist for the Hubble Space Telescope.
“The question we’re now trying to [answer] is, what fraction of stars actually harbor potentially habitable planets?” said Wiseman. Currently, only about four exoplanets detected by NASA’s Kepler mission appear to be terrestrial-sized and in the habitable zones of their parent stars, she said, although that number is growing quickly as more data are analyzed. Of those, only one orbits a sun-like star, but even that doesn’t mean it is necessarily Earth-like. When comparing exoplanets to our own environment and considering the possibility of habitability, we also have to remember that we may be seeing the other stellar system at a very different stage than that of the current earth—either younger or older, and that can mean very different environmental properties, she said.
Drawing on his expertise as an evolutionary biologist, Freeland said failure to disambiguate between the idea that the universe “is teeming with life” and the idea that it is “teeming with sentient, intelligent life” can lead to confusion.
There is no scientific basis for thinking that human beings are the end point of evolution, Freeland said. “Every species in today’s world is the successful product of four billion years of evolution. There is no such thing as more highly or less highly evolved [species].”
Building upon this evolutionary foundation, Freeland offered three “clues” for the existence of extraterrestrial life.
- Timing: A consensus has emerged in the geoscientific community over the last few decades that life on Earth “got off to a very early start,” he said. “The problem is that rocky planets should be dry planets … The formation of liquid oceans, almost like watering a barren piece of garden, seems to have led to life’s sprouting up remarkably quickly afterwards.”
- Prevalence: “It boils down to one word: extremophiles,” Freeland said. These organisms can live at the extremes of temperature, pressure, acidity, alkalinity, and even radioactivity. “There are far more of them, they’re far more diverse than we ever thought, and … they are living in environments which previously … we would have written off as impossibly hostile to life.”
- Composition: A mere six ordinary elements account for 99.9% of life’s chemistry, he said. “If life was freakish, if life was unusual and not to be expected, one sign of that might be that it takes some special ingredients to make it ... We see quite the opposite. Life is made of the most abundant, common, obvious stuff.”
“By these standards, there are all sorts of places within our own solar system that are habitable in some sense,” Freeland said. “Perhaps the most interesting, mind-blowing path of this discovery of life’s coexistence with other planets is to discover that our concept of habitability is all kinds of wrong. We used to think that you needed the right kind of planet for life. We now think that life changes the planet and that our planet largely reflects the presence of life in key attributes.”
Nonetheless, he cautioned against believing that we can currently know with certainty how much life there is in the universe. “It is still a deeply polarizing topic to talk about the extent to which our universe, or even our galaxy, is life-friendly,” he said.
Steven J. Dick, former NASA chief historian and incoming Baruch S. Blumberg NASA Chair in Astrobiology at the Library of Congress, put the debate about extraterrestrial life into historical context, tracing it from the Greeks through Copernicus, Descartes, Galileo, Bruno, Newton and Thomas Paine.
Newtonian natural theology is consistent with the idea that God’s magnificence supports “a large number of inhabited worlds,” Dick said. But other thinkers, including Paine, believed extraterrestrial life is inconsistent with Christian doctrine. “That set off the debate between natural theology and Christian doctrine that still has not run its course,” he said. “Today opinion is divided into at least two camps: those internal to religions, Christian or otherwise, who hold that their religion will adapt to the idea … of extraterrestrial life and those external to religious traditions [who] often look forward to the destruction of those religions when extraterrestrial life, especially extraterrestrial intelligence, is found.”
Dick said he believes that most religious groups will, over the long term, accept the discovery of life on other planets.
He advanced three “bedrock principles” for possible human responses to extraterrestrial life:
- We cannot predict the future.
- Society is not monolithic and so there will be a variety of impacts “depending on religious, cultural, and worldview aspects of each society.”
- The impacts will be “scenario dependent.” In other words, “The impact of the discovery of fossilized life or living microbial life will presumably be quite different from the impact of the discovery of extraterrestrial intelligence. And the latter will be different again if we receive a message, different yet again if we decipher a message, and very, very different depending on what the message says.”
History offers instructive analogues for these potential responses, Dick said. For example, he cited media speculation and theological discussion around the possible discovery of fossilized life on Mars.
“I do believe that the discovery of even microbial life … will have considerable impact over the long term both in theology and in our more secular worldview, just as Copernican and Darwinian worldviews have,” Dick said. “The question now is whether or not we live in a physical universe dominated by dead galaxies and stars and planets or whether we live in … [a] biological universe … where life is constituting a kind of biophysical cosmology … that asserts the importance of both the physical and the biological components of the universe, and posits, perhaps, a deep relationship between the two.”
The exciting result, he said, is that we find ourselves in a situation not dissimilar to when Western civilization was deciding whether we lived in a geocentric or a heliocentric universe. “That’s the significance of astrobiology today.”
Wiseman closed the discussion by fielding questions from the audience and adding one of her own. She asked Freeland if there is enough information right now to predict whether extraterrestrial life should be common or rare? “I think we don’t know,” Freeland said. “Everything that we’ve learned teaches me that we need to be a lot more humble about our pronouncements.”