Researchers from LMU's Excellence Cluster ORIGINS and the Max Planck Institute for Extraterrestrial Physics have identified a new pathway for habitability in the cosmos. Their study reveals that exomoons orbiting free-floating planets—worlds ejected from their original star systems—could maintain liquid water oceans without any stellar energy source.
The key to this remarkable longevity lies in two mechanisms: dense hydrogen atmospheres that provide insulation and tidal heating generated by gravitational interactions between the moon and its host planet. These forces work together to keep subsurface oceans in liquid form despite the absence of stellar radiation.
According to the research team's calculations, these conditions could persist for up to 4.3 billion years. This timespan is nearly equivalent to Earth's entire geological history and represents sufficient time for complex life forms to potentially evolve and develop.
The findings expand the traditional concept of habitable zones, which typically focus on planets orbiting within the "Goldilocks zone" of stars. By demonstrating that moons around rogue planets could sustain life-supporting conditions, the research suggests that habitable worlds might be far more common throughout the galaxy than previously thought.
This discovery could fundamentally reshape how astronomers search for life beyond our solar system, potentially directing attention toward the countless rogue planetary systems drifting through interstellar space.