How Astronomers Came to Think We Are Probably Not Alone

NASA has long suspected that life was possible, even likely, on other planets. The real importance of the Kepler news this week: more motivation to fund further exploration.
An artist's rendering of Kepler's planet candidates orbiting in front of their home stars (NASA)

To the average American, the news about NASA’s Kepler spacecraft discovering evidence of potentially “billions” of Earth-like planets in “habitable” solar orbits in the universe might feel like a paradigm-shifting moment. If there are billions of Earth-like planets out there, the possibility of life existing somewhere other than Earth suddenly goes from seeming like an odds-against to an odds-on notion.

But to NASA’s scientists, that paradigm had shifted long before the headlines hitindeed, before Kepler even launched.

While the majority of the public’s attention (and NASA’s funding) over the past decades was focused on the human spaceflight program, NASA’s astronomical science program slowly was chipping away at some of the biggest mysteries of the universe, including the origins of the elements necessary for life. By the time NASA was founded in 1958, astronomers had already figured out that all the heavier elements in the periodic table, which are necessary for life as we know it,not only could be produced, but actually were produced in the high-temperature supernova explosions of large stars. How those materials might be transported to potential planets in orbit around still-healthy stars, however, was still a mystery.

Ten years later, scientists began finding evidence of water and a variety of elements in interstellar space, which meant those elements could travel away from where they were formed. But that still didn’t account for getting enough of those elements onto a planet’s surface to spark life.

Enter the comets. By the late 1980s and early 1990s, research into the composition of comets had showed that comets contained—and released, at different points of their orbital trajectories—traces of all the elements necessary for not just life, but carbon-based life as we know it. One of the details of astronomy I find most fascinating is that every element in the periodic table produces its own unique “fingerprint” on the electromagnetic spectrum. So if you look at a cosmic object through a spectrographic instrument, you can tell, even from light years away, what elements it contains. (NASA’s Stardust mission, launched in 1999, confirmed the spectrographic notions about comets with actual material collected from the tail of the Wild 2 comet, returned to Earth in a parachute-equipped capsule.)

The existence of crucial elements in comets didn’t prove that comets provided the necessary link to delivering those materials to planets, but it made that theory more plausible. It became possible to envision a universe that not only created all the elements necessary for water, a survivable atmosphere, and carbon-based life forms, but also possessed a delivery system for getting those elements to a few perfectly-sized and composed planets, situated perfectly around perfectly-sized stars, and then occasionally combining in just the right timing and proportion to create a life-bearing planet like Earth.

But what were the chances of there being enough of those perfectly-situated, perfectly-suited planets to make life elsewhere not just possible, but plausible, or even probable?

In the fall of 1997, I interviewed a NASA astrophysicist by the name of John Mather for a book about the satellite-based scientific research conducted by NASA’s Goddard Space Flight Center. Mather had been the force behind the Cosmic Background Explorer (COBE) satellite that discovered scientific evidence supporting the Big Bang Theory of the universe’s origins. In 2006, Mather received a Nobel Prize for that research, but even in 1997 he was considered one of the most brilliant astrophysicists in the world. It’s not often you get access to a mind like that, so after I finished asking him about his research, I asked him what he thought about other big cosmic issues, including the possibility of life on other planets.

His eyes lit up. He answered that 10 years earlier, he and most of his colleagues felt that the chances of intelligent life existing elsewhere in the universe were remote. But two things, he said, had changed their views. Radically. He talked about the above-mentioned discoveries in terms of comets and the plausibility of critical elements being distributed to planets. And then, he said, came the Hubble Telescope’s first Deep Field image.

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Lane Wallace is a pilot and adventure writer. She is the author of Surviving Uncertainty: Taking a Hero's Journey.

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