Researchers affiliated with the Excellence Cluster ORIGINS at Ludwig Maximilian University of Munich (LMU) and the Max Planck Institute for Extraterrestrial Physics have put forth a novel location within the cosmos where life might potentially arise: the moons orbiting so-called rogue planets, those drifting through interstellar space without any nearby star.
What Are Rogue Planets?
Planetary architectures are born out of chaotic processes. When nascent planets aggregate in too close proximity, gravitational interactions can eject one of them completely from its system. Such celestial bodies, detached from a parent star, are termed rogue or free-floating planets. Earlier work by LMU physicist Julia Rocchetto demonstrated that gaseous giants flung from their systems might retain some of their attendant moons. Estimates suggest that such planets could be as numerous as stars within our Galaxy.
The Source of Heat
Once ejected, the orbits of these planets’ moons become highly elongated, resulting in a continuously fluctuating distance between the moon and its planet. This dynamic generates powerful tidal forces that repeatedly squeeze and stretch the moon’s interior. The resultant friction produces heat—sufficient warmth to maintain liquid water oceans even given the complete absence of starlight. Calculations by the scientists indicate this state could persist for up to 4.3 billion years, roughly mirroring the duration of life’s existence on Earth.
The Function of a Hydrogen Atmosphere
To prevent this warmth from dissipating into the vacuum of space, an atmosphere capable of trapping it is essential. While carbon dioxide serves this purpose on Earth, it would completely freeze out near rogue planets. The investigators explored an alternative: an atmosphere rich in molecular hydrogen. Under immense pressure, colliding hydrogen molecules can form transient structures that absorb and retain heat. Unlike carbon dioxide, hydrogen remains stable at extremely low temperatures, making it a reliable insulator.
Parallels with Early Earth
The study’s lead author, LMU doctoral candidate David Dahlbühdding, commented: “Our collaboration with Professor Dieter Braun’s team helped us realize that the cradle of life doesn’t absolutely necessitate the presence of a sun. We identified a clear link between these distant satellites and early Earth, where high hydrogen concentrations following asteroid impacts might have fostered conditions conducive to life’s genesis.” Additionally, the tidal forces could induce surface wetting and drying cycles, considered crucial prerequisites for the formation of complex molecules and the emergence of life.
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