Wandering Planets Could Support Life

July 1 -- Take Earth, gently fling it out of the solar system into the voids of interstellar space…

… and we’d die.

Without warming sunlight, temperatures would cool to minus 400 degrees Fahrenheit.

“Not a good place for life,” observes David Stevenson, a planetary scientist at the California Institute of Technology. (A few microbes that live a few miles underground and get their energy from Earth’s still-hot core might survive, but pretty much every other critter would freeze to death.)

Not to worry. Earth won’t be going anywhere anytime soon.

A Galaxy of Rogue Planets

But elsewhere in our Milky Way galaxy, there could be hundreds of billions of Earth-size planets adrift in the dark reaches of space. Ruminating about the fates of these lonely, lost worlds, Stevenson has concluded some of them could actually be cozy, if pitch-black, homes of alien life.

“This is not a discovery,” Stevenson, says. “It’s just an idea. And it’s fun.”

Stevenson reports on his fun idea in today’s issue of the journal Nature.

Planets coalesce from the disk of dust and gas left over after the birth of a star. Small clumps clump into larger clumps. Larger clumps clump into asteroid-size mini-planets, which then clump into planets.

But the gravitational tugging between planets and mini-planets likely swung many of them straight out of the neighborhood, like pebbles flying out of a slingshot.

Warm Blanket of Hydrogen

The difference between Stevenson’s hypothetical exiled worlds and the frozen wasteland that Earth would be in interstellar space lies in the atmospheres. Moving through clouds of hydrogen gas, Stevenson surmises the wandering planets could accumulate a dense blanket of hydrogen on the way out.

Under high pressures — as much pressure as at the bottom of Earth’s oceans — hydrogen acts like a thermal blanket, trapping heat from volcanic activity, and the trapped heat would keep the surface above freezing temperatures. (Earth’s atmosphere of nitrogen and oxygen doesn’t share that insulating quality.)