Dude, Where's My Planet?

It may sound strange, but it seems some planets are ejected from the solar system where they were born, while still in an early development stage, and set to wander the interstellar space. That's kind of a scary thought, even though actual pictures of such planets may look good.

Remember the sci-fi series of the 70s called Space: 1999, depicting the journey of the occupants of a Moon base after the Moon is knocked out of orbit by a nuclear explosion? It seems this could happen to planets, and by natural causes.

Theoretical astrophysicists Mario Juriæ and Scott Tremaine of the Institute for Advanced Study in Princeton, New Jersey wrote a paper about the drifting planets and they say that the number of homeless planets drifting through interstellar space may actually exceed the number of planets orbiting stars.

Nobody really knows why most giant planets have elliptical orbits, unlike the almost circular ones of Jupiter and Saturn, so the two scientists tried to explain this mystery.

By performing computer simulations of the evolution of young planetary systems containing a few dozen massive planets, they found out that gravitational attraction between neighboring planets further distorts the elliptical orbits and eventually flings the objects away.

So, it seems that over tens of millions of years, systems in which the giants have a random and chaotic collection of orbits lose most of these planets, and only two or three giants remain, each having an elongated elliptical orbit.

"Our model predicts that systems with a giant planet in an elongated orbit are unlikely to harbor more than one or two additional giant planets," said Juriæ.

Finding such planets is extremely hard since they don't orbit a star, thus the usual detection methods, relying on the light they block when passing in front of the star, don't really work. They are just cold and dark space objects that are almost impossible to spot without a light source illuminating them.