[LINK] "Alien Planets Outnumber Stars, Study Says"

[rfmcdonald]

I like National Geographic's coverage of the fact that, yes, rogue planets--planets unattached to stars--are quite common.

If you look to the stars tonight, consider this: No matter how innumerable they may seem, there are far more planets than stars lurking out there in the darkness, a new study suggests.

The study uncovered a whole new class of worlds: Jupiter-like gas giants that have escaped the gravitational bonds of their parent stars and are freely roaming space.

What's more, "our results indicate that such planets are quite common," said study team member David Bennett, an astronomer at Notre Dame University in Indiana.

"There's a good chance that the closest free-floating planet is closer to Earth than the closest star."

Ohio State University astronomer Scott Gaudi added, "It's not surprising that free-floating planets are out there"—they've been predicted by planet-formation theories for years—"it's just how many of them that they're finding."

The findings, detailed in this week's issue of the journal Nature, indicate there are about two free-floating planets per star in our galaxy—and perhaps in other galaxies, too.

Scientists estimate there are about 200 billion stars in the Milky Way, so that means there could be at least 400 billion drifting planets in space. And that's not even counting the planets that orbit stars, or smaller, rocky free-floaters that can't yet be detected.

"These are just the ones that we found," study co-author Bennett said. "If we could see lower-mass planets, then presumably the number would be even larger."

The team's use of gravitational lensing--briefly, the temporary warping of space by a passing large body that helps magnify a distant object in between greatly--is responsible for the confirmation of this. These rogue planets can be ejected from normal planetary systems by regular means, or--I myself suggest--might form by themselves via the same processes as stars.