A new study by astronomers working with the Kepler Space Telescope suggests that our galaxy contains at least 100 billion alien planets.
“It’s a staggering number, if you think about it,” says lead author Jonathan Swift of California Institute of Technology in Pasadena, California. “Basically there’s one of these planets per star.”
Swift’s team has been observing a five-planet system dubbed Kepler-32 that lies about 915 light-years from Earth. NASA’s Kepler Telescope detected the alien exoplanets by flagging tiny reductions in brightness when the bodies crossed their system’s star.
The star at the center of the Kepler-32 system is an M dwarf, the most common type in the Milky Way galaxy. These dwarfs, smaller and cooler than our sun, account for an estimated 75 percent of the 100 billion stars filling the near-cosmos, according to researchers.
The five worlds recorded in Kepler-32 are of comparable size to Earth, but orbit relatively close to their parent star. This makes them representative of most systems involving M dwarfs, according to numerous observations made over Kepler’s nearly 4-year lifespan.
“I usually try not to call things ‘Rosetta stones,’ but this is as close to a Rosetta stone as anything I’ve seen,” remarked the study’s co-author John Johnson, also of Caltech. “It’s like unlocking a language that we’re trying to understand—the language of planet formation.”
The estimate of 100 billion planets is actually a conservative figure. The team’s analysis didn’t include outer worlds in M-dwarf systems, or planets circling other types of stars. According to Swift, the Milky Way may in fact be home to 200 billion planets or more, or about two per star.
Kepler can only detect planets with orbits around their stars that happen to align with the telescope. To account for this, the team calculated the odds that an M dwarf planetary system would be oriented edge-wise to Kepler’s lens, and combined that with the number of planets detected in such systems thus far. The resulting figure was roughly 100 billion.
All of Kepler-32’s planets orbit within 10 million miles of their star, compared with Earth’s average distance of 93 million miles from the sun. The five planets are not as super-heated as that difference might imply, however, due to the dwarf’s smaller size and lesser radiation output.
In fact, the system’s outermost planet may lie within the ‘just right’ habitable zone, where liquid water could theoretically exist on the surface without freezing or instantly evaporating.
The study’s prediction of 100 billion planets is admittedly a rough estimate, representing the first attempt to translate Kepler’s observations into an actual figure. Most of the 3,000 exoplanets identified by the telescope have yet to be confirmed, though the team estimates that at least 80 percent will prove to be the real deal.
The actual number could fall below, or well above, 100 billion. With those kinds of odds, many scientists are hopeful that at least one such world could support indigenous alien or future human life.
“The Earth isn’t unique, nor the center of the universe,” said University of California, Berkeley professor and veteran planet-hunter Geoff Marcy, in a recent interview with Space.com. “The diversity of other worlds is greater than depicted in all the science fiction novels and movies. Aristotle would be proud of us for answering some of the most profound philosophical questions about our place in the universe.”
Since launching in March 2009, the $600 million Kepler mission has observed more than 150,000 stars in its tireless search for transiting exoplanets.
Having recently completed its primary mission, NASA has granted funding for an extended mission to 2016, and possibly beyond. Whereas prior data was held as proprietary by the Kepler team for a period of several months, all data received and processed from now on will immediately be made public.
The new study was published January 2 in The Astrophysical Journal.