Objects with masses (<0.08 solar masses) too small to sustain hydrogen fusion were theorized to exist five decades ago, and discovered 30 years later, due to their extreme faintness. Even less massive (<13 Jupiter or <0.01 solar masses) are the planetary mass objects (PMOs, so-called because they are not orbiting a star.
We have recently discovered large populations of such free-floating PMOs and brown dwarfs in the nearest star-forming regions to Earth, when they are at their brightest and most amenable to detection.
Do such objects outnumber the stars in the Galaxy? Do they have their own planetary or moon systems?
Could these sustain surface or subsurface liquid water for eons via tidal heating and thus provide environments conducive for the development of microbial life?