Nearly 10,000 light years away, a planet the size of Saturn is floating all on its own through empty space. In a stroke of luck, researchers were able to spot this strange, dark world using both ground-based telescopes and the Gaia space telescope, allowing them to measure the mass of a free-floating, or rogue, exoplanet for the first time.
Most rogue worlds that have been found are either more massive than Jupiter or lighter than Neptune, leaving in the middle a gap in size that researchers refer to as the “Einstein desert”. This has generally been attributed to the idea that lighter-than-Neptune worlds are relatively easy to eject from pre-existing orbits around stars, whereas planets more massive than Jupiter don’t have to form inside traditional planetary systems, but can sometimes form similarly to stars in free space