Whose Galaxy Is It?

As astronomers discover a universe flush with potentially life-supporting planets, it seems more and more likely that we are not alone.

by Caleb Scharf Published Winter 2014-15
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Like many scientific revolutions, the one occurring now in this interdisciplinary field of astrobiology is fueled by technological innovation. Yet the next challenge we face puts us in a cosmic Catch-22. If we are to ascertain whether life exists on one of these distant planets, we need to build even more sensitive telescopes. And yet to design the right telescopes, we need to learn more about what we’re looking for. We need to figure out ahead of time what kinds of clues are indicative of an active biosphere.

To address this question, astrobiologists and astrophysicists are now collaborating with climate scientists, whose computer models of Earth are being adapted to create virtual alien worlds. Some of this work is being pioneered at Columbia, where researchers led by Anthony D. Del Genio, an adjunct professor of earth and environmental sciences and a member of the NASA Goddard Institute for Space Studies, are building simulations of hypothetical planets replete with pulsing atmospheres, oceans, and starlight to provide them with energy. To test their methods, they are creating simulacra of ancient Mars, ancient Earth, and ancient Venus. Millions of lines of computer code are being scrutinized and updated. Soon the scientists will build ice worlds, ocean planets, bigger Earths, smaller Earths, some spinning rapidly and others slowly, some frothing with biological activity and others barren. Hopefully these models will help teach us how to detect life’s fingerprints: atmospheric imbalances of compounds like oxygen or methane, or perhaps the infrared energy leaking from technological civilizations. As these virtual worlds are permitted to take their imaginary course, Del Genio and his colleagues will learn how to build tools to discriminate between habitable and uninhabitable worlds.

In searching for life outside our solar system, astrobiologists have until now focused mainly on observing planets that orbit stars similar to our sun in age and composition. But many of us believe that we could be limiting ourselves unnecessarily. To get a better idea of what star systems are worth investigating, we are now working with scientists who study the chemistry of both the ancient universe and the frigid interstellar regions where stars and planets form. Among these researchers is Columbia astrophysicist Daniel Wolf Savin ’85CC, who has built a sophisticated experiment at the University’s Nevis Laboratories in Irvington, New York, in which he re-creates the harsh conditions of interstellar space and then tries to coax delicate molecules like water and carbon compounds into being. By measuring the ease with which these reactions take place, he is giving us a better idea of what environments might sustain the full range of elements and organic materials necessary for life as we know it.

“Who is to say that life must consist of discrete, self-replicating organisms that move around independently, competing, cooperating, and mating with one another?”

What might extraterrestrial life be like, should we find it? The truth is that we have absolutely no idea. If the study of distant planets has taught us anything so far, it is that diversity rules. A rainbow of cosmic conditions exists: variations in chemistry, climate, and the vagaries of each planet’s unique history. Even if life here on Earth is built from a universal toolkit, it seems possible that life could turn up in altogether unfamiliar forms elsewhere. Who is to say, for instance, that life must consist of discrete, self-replicating organisms that move around independently, competing, cooperating, and mating with one another? Might it instead be a dispersed web of organic material that metabolizes energy, processes sensory information, and thinks as a unified entity — not unlike a biological version of our vast Internet? The ideas of science fiction could yet turn out to be reality. It is useful to remember that life on Earth is the result of a particular chain of evolutionary events that, in hindsight, seem miraculously serendipitous. If this story were written on another world, around another star, beginning at another moment in the universe’s history, the outcome might shock us.

Some surprises may come from environments right here in the solar system. Icy moons like Jupiter’s Europa and Saturn’s Enceladus erupt with geyser-like plumes of salty water, offering a taste of what must be immense interior oceans. There is now intense interest in whether the bases of these abyssal realms, where water meets rock hundreds of miles down, might create analogs to the hydrothermal systems we find on Earth. Are these places where cave-dwelling life can flourish? Some scientists have suggested that life on Earth could have originated in parts of the deep terrestrial biosphere, which calls into question whether the same could have happened in a moon like Europa. Meanwhile, some of us are wondering if life on Earth might have originated elsewhere, perhaps on Mars or some nearby icy moon, and migrated here — or alternately, if simple Earth organisms might have at some point colonized a neighboring planet or moon. We’re dreaming up experiments to test the ability of microbes to survive transfer between worlds on chunks of material chipped from planets by asteroid impacts, tests that could one day fly on the International Space Station.

It may also be the height of conceit to think that terrestrial life couldn’t originate multiple times from scratch, perhaps even rewiring the basics of biology each time. Some scientists today are searching Earth for evidence of what is commonly called “weird life,” or life forms that utilize alternative biochemistries and thus evade our normal tools for studying living things. A few years ago the possibility of arsenic-based life in a California lake made headlines, and although it turned out to be spurious, many astrobiologists continue to believe there is value in challenging the status quo.

Preparing for the unexpected in astrobiology isn’t just a psychological exercise; it’s a critical part of the scientific process. We’ve only had one history, one living planet, to work with so far. Change this and you change the rules of the game.


Caleb Scharf is the director of the Columbia Astrobiology Center and an adjunct associate professor of astronomy. He writes Scientific American’s Life, Unbounded blog and is the author of several popular books on astronomy, including, most recently, The Copernicus Complex.

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