|Artist's conception of the Kepler telescope. (NASA/Ames/JPL-Caltech/HO)
A new study out of the California Institute of Technology says there are more than 100 billion planets in the galaxy — an estimate the researchers call conservative.
"There's at least 100 billion planets in the galaxy — just our galaxy," co-author John Johnson said. "That's mind-boggling."
The researchers came up with the number by analyzing planets orbiting a star called Kepler-32.
Kepler-32, so named because it was discovered with the telescope Kepler, is an M dwarf — the type of star that makes up about three-quarters of all stars in the galaxy.
Scientists believe the planets orbiting Kepler-32 are representative of most planets in the Milky Way.
First, the scientists determined the probability that an M dwarf system would provide Kepler-32's planetary orientation. Then, they combined that probability with the number of planetary systems Kepler is able to detect, concluding there's one planet for every one of the approximately 100 billion stars in the galaxy.
"It's a staggering number, if you think about it," lead author Jonathan Swift said.
And that's a conservative estimate, they say, because it doesn't take into account the planets that orbit other kinds of stars, or even the ones in the outer orbits of M dwarfs.
"It's really fundamental from an origins standpoint," Swift said. "Kepler has enabled us to look up at the sky and know that there are more planets out there than stars we can see."