The concept of life beyond our solar system has long been a subject of fascination and scientific inquiry. Traditionally, the search for extraterrestrial life has been centered around stars and the habitable zones they provide. However, a recent study challenges this conventional view, suggesting that life might not necessarily require a star to thrive. The research, published in the paper 'Life in the dark: Potential urability of moons of rogue planets', explores the possibility of subsurface oceans on moons orbiting rogue planets, which are planets not gravitationally bound to any star.
The study, conducted by Viktória Fröhlich and Zsolt Regály, focuses on planets ejected from their star systems during supernova explosions. These rogue planets can be thrown into interstellar space due to gravitational encounters, stellar evolution, or the violent mass loss that follows a supernova. The key question addressed is whether any moons orbiting these rogue planets could survive the supernova event and remain bound to their planets.
Through simulations, the authors found that the moons indeed remained bound to their planets after the supernova. This is a crucial finding, as it opens up the possibility of these moons retaining subsurface oceans for billions of years, even without the presence of a star.
The study relies on tidal heating, a process already observed in our solar system. When a moon travels around a larger body on a slightly stretched orbit, gravity pulls on it unevenly, causing mechanical deformation and the dissipation of energy as heat. The authors compare this process to Europa and Enceladus, moons of Jupiter and Saturn, respectively, which are known to have subsurface oceans.
The results indicate that in approximately 12-15% of the simulated cases, the tidal heating power on these rogue-planet moons falls within a range comparable to that of Europa or Enceladus. This success is not random but rather depends on the moon's proximity to its planet and its orbital eccentricity, allowing for repeated flexing.
One of the most intriguing aspects of this study is the timescale involved. The orbital eccentricity of these moons can remain significant for billions of years, far exceeding the age of our solar system. This means that subsurface oceans on these moons could potentially exist for extended periods, even without a sunrise.
However, it's important to note that this study does not prove the existence of life on these moons. The term 'urability' is used to describe the conditions that might allow life to begin, rather than simply conditions where existing life could persist. The study's value lies in raising the question of whether these moons could support the necessary conditions for life to emerge.
The challenge of detecting these rogue planets and their moons is also discussed. Without starlight, these systems are difficult to observe directly. Indirect methods such as microlensing, thermal emission, or future techniques sensitive to planet-moon signatures may be required to detect them. Even if these moons exist, inferring the presence of subsurface oceans and, ultimately, life, would be a complex and challenging task.
In conclusion, this study expands our understanding of potential habitable environments beyond the traditional star-centered view. It suggests that deep space might not be as inhospitable as previously thought, and that subsurface oceans on moons orbiting rogue planets could provide pockets of liquid water for extended periods. This research opens up new avenues for exploration and highlights the importance of considering a wider range of celestial bodies in the search for extraterrestrial life.
