We usually defined a planet as something that orbits a star but this lone ranger a.k.a. nomad planet, rogue planet, free-floating planet, or orphan planet is unique since they do not orbit a star. Instead, they orbit the galaxy directly and considered as homeless world where they have neither sunrises nor sunsets (starless planet).
What Are Rogue Planets by YouTube
Migration appears to be quite common for planetary systems like the Jovian-type planets that migrate inward in some planetary systems due to close gravitational encounters in which one object loses energy and moves inward while other object gains energy and flung outward. Hence, it is reasonable to expect many planets have been ejected from their planetary system into interstellar space.
These planets are so difficult to detect directly because they are so dim, but how on Earth could we find them?
The best method for now is by using technique called gravitational microlensing. This technique takes advantage of gravity’s ability to bend light. These occur when massive object like a rogue planet passes between a star and Earth, the “lone ranger” acts as a lens which make the star’s light curve as seen from Earth. The lone ranger’s gravity warps the light of the background star causing it to magnify the same way as the lens work. In general, the bigger the planet, the more affected the light causing brightening events that can last for weeks which is way longer than small planets only last for few days or less.
One observational search found that these lone ranger might be twice as numerous as the stars in our galaxy. Therefore, the studies of the “lone ranger” are still going on and perhaps in the future, one of these planets could be Earth 2.0 .