Just one generation ago, the thought of finding a planet that might support life was the stuff of science fiction. Last week, NASA scientists announced they’d discovered a whopping 1,235 potential planets orbiting faraway stars, using the Kepler space telescope. If confirmed, this would almost triple the number of known planets outside of our solar system (called “exoplanets”), which currently stands at just over 500. “What we’re anxious to learn is whether there’s other life in our galaxy,” says Kepler co-investigator Natalie Batalha. She and other members of the team are trying to learn whether planets like our own are abundant or rare. “The answer will drive all future missions,” she says.
Among Kepler’s haul were 54 possible planets in the habitable zone, where temperatures could allow for liquid water at the surface, which is necessary to support all life as we know it. Five are close in size to Earth, and orbit in the habitable zone of stars that are smaller and cooler than our sun. The rest range in size from so-called “super-Earths” (up to twice the size of our planet) to ones bigger than our solar system’s kingpin, Jupiter. Most of Kepler’s findings still need to be confirmed as actual planets, but it’s almost certain the vast majority of them will be.
The mission’s goal is to find other planets like Earth, but along the way, we’re finding all sorts of things we didn’t expect: like a system of six confirmed planets orbiting a sun-like star called Kepler-11, packed so tightly together that, according to Jack Lissauer of NASA Ames Research Center, who led the work on Kepler-11, “we didn’t know such systems could even exist.” It’s becoming clear that the universe is much more diverse, and more prolific, than we ever imagined.
Launched in March 2009, the Kepler space telescope orbits our sun and stares unblinkingly at some 156,000 stars—which range from a few hundred to a few thousand light years away—searching for the telltale winking of light that might signal a planet passing in front, like a moth flying by a porch light. It’s taking a sample from one neck of the Milky Way galaxy, from which planet hunters hope to discover whether Earth twins are statistically common or not. “We ultimately want to look for life,” says Kepler co-investigator Dimitar Sasselov, who leads Harvard University’s Origins of Life Initiative. “This is how we get to that point.”
Kepler is only looking at one-400th of the sky, a small sliver of the Milky Way—which, in turn, is one of countless galaxies in the universe. All these possible planets were found in that one area within just the first six months of its mission (from May to September 2009), which is slated to last 3½ years at least. With so many planets being found so fast, and with 54 of these possibilities in the habitable zone, it looks almost certain that there are more planets like our own out there. And we’ve only just begun to look. One can’t help but feel that our view of the universe—and whether or not we’re alone—is different today than it was just one week ago, before NASA announced Kepler’s findings.
“It’s a golden age for astronomers,” says Jaymie Matthews, a professor of astronomy and astrophysics at the University of British Columbia. “I’m personally convinced that 400 years from now, people will look back at this era—even this past decade—in the same way we look back at the times of Copernicus, Kepler and Galileo. We’re the first generation in the history of our species capable of searching for another Earth. And we’ve only had that capability for a few years.”
Imagine looking out at the Empire State building at night, with all its window shades open and the windows lit up from the inside. Now, imagine the dip in brightness that would occur if one person stood at one of those windows, and pulled down one window shade by just seven centimetres. “Kepler was designed to measure light variations to that level in a bright star,” Matthews says, “and even smaller.”