Life in the dark

Context. Free-floating (rogue) planets are thought to be numerous in the Galaxy and may retain their moons after ejection from their natal systems. If those satellites acquire or preserve orbital eccentricity, tidal dissipation can provide a long-lasting internal heat source, potentially creating urable environments (capable of enabling abiogenesis) in the absence of stellar radiation. Aims. We explore (i) whether moons remain dynamically bound to planets expelled by a core-collapse (Type II) supernova, (ii) how the explosion reshapes their orbits, and (iii) under which circumstances tidal heating can sustain urable subsurface oceans that meet the minimal conditions for life to originate. Methods. We carried out 4412 three-dimensional N-body simulations with an 8th-order Runge–Kutta scheme, modelling homologous stellar mass loss for progenitors of 10 M⊙. Post-explosion orbital elements of single moons and resonant moon systems were analysed, and tidal heating power was estimated with a constant phase-lag prescription for several tidal dissipation functions and moon densities. Results. All simulated moons survive the supernova and remain bound to their planets. The explosion excites moon eccentricities up to ≃7 × 10−4 and ≃3 × 10−3 for single moons of planets with circular and eccentric orbits, respectively. For resonant pairs, an eccentricity of ≲2 × 10−2 is preserved. The semi-major axis of the moons changes by ≲0.2%. For 12–15% of cases – preferentially moons at a ≤ 15 Rp and with e ≥ 10−3 – the specific tidal heating power lies between 0.1 and 10 times what is estimated on Europa or Enceladus, sufficient to maintain liquid oceans beneath an ice crust. Eccentricity damping timescales exceed the age of the Solar System for a ≥ 10 Rp, implying billions of years of continuous heating on the moons. Conclusions. Moons of rogue planets ejected via Type II supernova explosions are both dynamically stable and, in a significant minority of configurations, tidally active enough to host long-lived subsurface oceans. Such worlds represent promising targets for future searches for extraterrestrial life.