It’s hard to say what’s hidden out there, within the dark voids between stars .
Evidence, however, suggests the existence of a huge population of rogue exoplanets, set adrift and tethered to no star. Faraway from the live-giving warmth a star provides, these lonely exoplanets are unlikely to be habitable.
Their moons could be another story.
According to new mathematical modeling, a number of those moons – a minimum of , those with very specific conditions – could potentially harbor both atmospheres & liquid water, because of a combination of cosmic-radiation and therefore the tidal forces exerted on the moon by the gravity or gravitational interaction with its planet.
While it’s difficult to catalog exoplanets generally , never mind exoplanets unattached to a star, surveys have identified candidates by studying the gravitational effect these exoplanets should have on distant starlight.
Estimates from these surveys suggest there could also be a minimum of one rogue Jupiter-sized giant gas exoplanet for each star within the Milky Way .
If so, that’s a minimum of 100 billion rogue exoplanets – and former research found that a minimum of a number of these rogue exoplanets could are yeeted out of their home system along-with an exomoon. (We’ve not yet conclusively detected an exomoon, but given the preponderance of moons within the solar-system , the existence of exomoons is about certain.)
Here on Earth, most life relies upon a food cycle resting on a foundation of photosynthesis – that’s , it absolutely requires the light & warmth of the Sun. This heat is additionally what helps keep the water on Earth surface liquid – a prerequisite for all times as we all know it.
Yet, out beyond the Solar System’s frost line, where liquid water is predicted to freeze, there are places where it can still be found. These are the ice moons Ganymede and Europa, in orbit around Jupiter, and Enceladus, in Saturnian orbit.
Although encased in thick shells of ice, these moons harbor liquid oceans below their surfaces, thought to be kept from freezing by internal heat generated by the stretching & squeezing exerted by the planets’ field because the moons orbit.
Thus, it’s thought that Europa and Enceladus might harbor life. Although shielded from sunlight, there’s a kind of ecosystem here on Earth that does not believe the photosynthetic food cycle – the hydrothermal vents, where heat & chemicals escape from Earth’s interior, into lowest bottom of the ocean.
Around these vents, bacteria that harness energy from chemical reactions thrive; on those bacteria, other organisms can feed, building an entire new food cycle that does not involve sunlight in the least .
So, a team of scientists led by astronomer Patricio Javier Ávila of the University of Concepción in Chile sought to model the possibility of such exomoons existing around rogue giant gas exoplanets.
Specifically, an exoplanet the mass of Jupiter, hosting an exomoon the mass of Earth with an environment that’s 90% CO2 & 10% hydrogen, over the system’s evolutionary history.
Their findings suggest that a big amount of water are often formed within the exomoon’s atmosphere, and retained in liquid form.
Cosmic radiation would be the major driver of chemical kinematics to convert hydrogen and CO2 into water. this is able to produce 10,000 times less water than Earth’s oceans, but 100 times quite the atmosphere – that, the researchers said, would be sufficient for all times .
Tidal forces from the exoplanet’s gravity would then generate much of the warmth required to keep the water liquid. Even more heat might be contributed by CO2 within the exomoon’s atmosphere, which could create a greenhouse effect phenomenon to also help keep the planet temperate.
“The presence of water on the surface of the exomoon, effect by the capability of atmosphere to stay a temperature above the melting-point , might favor the growth of prebiotic chemistry,” the researchers wrote in their paper.
“Under these conditions, if the orbital parameters are stable to ensure a continuing tidal heating, once water is formed , it remains liquid over the whole system evolution, and thus providing favorable conditions for the emergence of life.”
The research has been published in the International Journal of Astrobiology.