Scientists have found planets with masses similar to Jupiter's so far from any stars, they believe the planets are roaming on their own.
How Do They Know That?
They used a technique called gravitational microlensing to track planets. When a foreground planet passes in front of a distant, background star, it acts like a lens and magnifies the star, displaying a specific light curve.
The height of the light curve's magnification and the length of time it takes to pass in front of the star, indicate the size of the planet.
Reach For The Stars...
Doesn't the planet have to pass in front of a lot of stars before they know if it's orbiting a sun or roaming?
Yes, that's why scientists came up with the MOA, the Microlensing Observations in Astrophysics study. The team monitored fifty million Milky Way stars for about two years, checking each star about once an hour for changes.
Then they added their data to OGLE, the Optical Gravitational Lensing Experiment to detect roaming planets. After all their analysis was done, they found almost five hundred short duration microlensing events that indicated planets. They also concluded that many of the planets were rogues.
So Long Pluto
So, if the planet doesn't orbit a sun, can it still be called a planet? I mean, look what happened to Pluto. Maybe they'll just be called rogues and not planets after all. Either way, I think it's cool to be a rogue.