The planet is a tramp

Image: © Jan Skowron / Astronomical
 Observatory, University of Warsaw.

An Earth-size planet is careening untethered through the galaxy, but nobody has ever seen one here — yet.

We know very well earth orbits the sun like a ship sailing in circles around its anchor.   But least one star flyes helplessly and heedlessly through interstellar space ans a planet goes rogue.

Either we were very lucky, or such objects are very common in the Milky Way. They may be as common as stars, 

wrote Live Science.

Earth orbits the sun like a ship sailing in circles around its anchor. But what if someone — or something — cut that ship loose? Unbound from any star or solar system, what would become of a tiny world flying helplessly and heedlessly through interstellar space? What happens when a planet goes rogue?

This discovery demonstrates that terrestrial-mass free-floating planets can be detected and characterized using microlensing.

Some low-mass planets are expected to be ejected from their parent planetary systems during early stages of planetary system formation. 

Although in practice such objects do not emit any light, they may be detected using gravitational microlensing via their light-bending gravity.