The search for extraterrestrial life has traditionally focused on planets orbiting stars, but a recent study challenges this conventional wisdom. The research, published in the paper 'Life in the dark: Potential urability of moons of rogue planets', suggests that moons orbiting rogue planets, ejected from their star systems during supernova explosions, could potentially harbor subsurface oceans for billions of years. This groundbreaking finding opens up new possibilities for understanding the conditions necessary for life beyond our solar system.
The study, conducted by Viktória Fröhlich and Zsolt Regály, focuses on planets ejected from their star systems due to the violent mass loss following a supernova. These rogue planets, without a gravitational bond to a star, can carry their moons into deep space. The key question addressed by the research is whether these moons can remain bound to their planets and whether they can maintain subsurface oceans despite the absence of sunlight.
The authors' simulations revealed that the moons remained bound to their planets even after the supernova. This is a crucial finding, as it suggests that the moons could potentially survive the extreme conditions of interstellar space. However, the moons would lack sunlight, and their surfaces would be frozen, making the subsurface oceans a critical source of warmth and potential habitability.
The study relies on tidal heating, a process already observed in our solar system. When a moon orbits a larger body on a slightly stretched orbit, gravity pulls on it unevenly, causing mechanical deformation and the dissipation of energy as heat. The researchers compared this process to Europa and Enceladus, moons of Jupiter and Saturn, respectively, known for their subsurface oceans.
The results indicated that in approximately 12 to 15 percent of the simulated cases, the tidal heating power fell within a range comparable to that of Europa or Enceladus. These successful cases were characterized by moons orbiting relatively close to their planets and maintaining sufficient orbital eccentricity for repeated flexing. This orbital irregularity becomes a crucial factor in sustaining tidal heating.
One of the most striking findings of the study is the timescale involved. Tidal heating diminishes as an orbit becomes too circular, and the internal heat source weakens. However, for moons at distances of at least about 10 planetary radii, the damping timescale for orbital eccentricity could exceed the age of the Solar System. This means that some of these moon systems could maintain the necessary orbital distortion for billions of years, potentially preserving subsurface oceans.
It's important to note that the study focuses on subsurface oceans beneath ice crusts, as a moon drifting through interstellar space would still be dark and externally cold. The term 'urability' is used to describe conditions that might allow life to begin, rather than simply conditions where existing life could persist. The research does not prove the existence of life, but it demonstrates the physical plausibility of sustaining subsurface oceans in certain scenarios.
However, there are significant challenges in detecting and confirming these hypothetical moons and their subsurface oceans. Rogue planets in interstellar space are difficult to find, and moons around them are even harder to detect. The study acknowledges that while rogue planets may be numerous, individual systems are not easy targets for observation. Indirect methods such as microlensing, thermal emission, and future techniques sensitive to planet-moon signatures may be required to detect these systems.
Furthermore, even if such moons exist, the oceans discussed in the study would be buried beneath ice crusts, making it challenging to infer their presence through telescopes. The study emphasizes that while it shifts the question from 'does life need a star?' to 'what kinds of worlds can keep energy flowing long enough for chemistry to continue?', it is still a long way from proving the existence of life on these hypothetical moons.
In conclusion, this study challenges the traditional view of habitability by expanding our understanding of where life might exist. It suggests that subsurface oceans on moons orbiting rogue planets could potentially sustain life for billions of years, even in the absence of a star. While the findings are theoretical and based on simulations, they open up exciting new avenues for exploration and research in the search for extraterrestrial life.
