Miraculous Conception: Are Planets Forming Without Stars?
One of the most remarkable discoveries about exoplanets—planets that exist outside of our solar system—is that some of them appear to be flying through interstellar space on their own. They’re not orbiting a star, nor are they tied to any other obvious companion.
The precise number of these planets—alternately called “free-floating,” “Steppenwolf,” “unbound,” or “rogue” worlds—is debatable, but it could be enormous. Some data gathered from gravitational-microlensing surveys suggests that there could be one to two times as many of these interstellar voyagers as there are stars in the Milky Way, which would be a number in the hundreds of billions.