How many rogue planets wander through our galaxy without a star?

The answer

Rogue planets - worlds wandering through interstellar space without orbiting a star - may be extraordinarily numerous in the Milky Way. Gravitational microlensing surveys by the MOA and OGLE collaborations suggest there could be billions of free-floating planets in our galaxy, possibly outnumbering stars. In 2023, JWST discovered approximately 540 planetary-mass objects in the Orion Nebula, including 80 puzzling pairs called Jupiter Mass Binary Objects (JuMBOs) that challenge formation theories since they are too small for gravitational fragmentation of molecular clouds. Rogue planets form through ejection from planetary systems during gravitational interactions or direct collapse of small gas clouds. Despite having no starlight, some could retain subsurface oceans heated by radioactive decay or tidal forces from captured moons, making them theoretically habitable. NASA's upcoming Roman Space Telescope will conduct a comprehensive microlensing survey expected to detect thousands of rogue planets.