There are at least 100 billion planets in our galaxy, according to astronomers at the California Institute of Technology.

Look up at the night sky and you'll see stars, sure. But the sky is also filled with planets - billions and billions of them at least.

That's the conclusion of a new study by astronomers at the California Institute of Technology (Caltech) in Pasadena, which provides yet more evidence that planetary systems are the cosmic norm.

Team members made their estimate while analyzing planets orbiting a star called Kepler-32 - planets that are representative, they say, of the vast majority of planets in our galaxy and thus serve as a perfect case study for understanding how most of these worlds form.

"There are at least 100 billion planets in the galaxy, just our galaxy," says John Johnson, assistant professor of planetary astronomy at Caltech and coauthor of the study, which was recently accepted for publication in the Astrophysical Journal. "That's mind-boggling."

For more on the study, see the NASA press release.