Hundreds of billions of planets the size of Jupiter are floating alone in space, or are so very far from their host stars that those stars aren't easily identifiable as associated with the planets. From the NY Times:
“It’s a bit of a surprise,” said David Bennett, a Notre Dame astronomer, who was part of the team. Before this research, it was thought that only about 10 or 20 percent of stars harbored Jupiter-mass planets. Now it seems as if the planets outnumber the stars…
Planetary astronomers said the results would allow them to tap into a whole new unsuspected realm of exoplanets – as planets outside our own solar system are called – causing scientists to re-evaluate how many there are, where they are and how they are created, even as astronomers immediately began to ponder whether the new planets in question are in fact floating free or just far from their stars, at distances comparable to those of Uranus and Neptune in our own solar system.
“Either there is a large population of Jupiter-mass planets far from their star, or, yes, there are a lot of lonely planets out there,” said Sara Seager, a planetary theorist at the Massachusetts Institute of Technology.
"Billions of Lonely Planets, Adrift in Space" (Thanks, Jody Radzik!)
