Miraculous Conception: Are Planets Forming Without Stars?
One of the most remarkable discoveries about exoplanetsâ€”planets that exist outside of our solar systemâ€”is that some of them appear to be flying through interstellar space on their own. Theyâ€™re not orbiting a star, nor are they tied to any other obvious companion.
The precise number of these planetsâ€”alternately called â€œfree-floating,â€ â€œSteppenwolf,â€ â€œunbound,â€ or â€œrogueâ€ worldsâ€”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.