https://www.scientificamerican.com/article/rogue-rocky-planet-found-adrift-in-the-milky-way/

Not all planets orbit stars. Some are instead “free-floating” rogues adrift in interstellar space after being ejected from their home systems. For decades astronomers have sought to study such elusive outcasts, hoping to find patterns in their size and number that could reveal otherwise hidden details of how planetary systems emerge and evolve.

Of the handful known so far, most free floaters have been massive gas giants, but now researchers may have found one small enough to be rocky—smaller even than Earth. If its rogue status is confirmed, the roughly Mars-to-Earth-mass object would be the most diminutive free-floating planet ever seen. Yet finding such small worlds could soon become routine, thanks to NASA’s upcoming Nancy Grace Roman Space Telescope, set to launch in the mid-2020s.