I was listening to a talk by astrophysicist Dr. Moiya McTier in which she stated that a rouge planet with a moon could harbor life – even create life.
Far be it from me, a lowly pobe, to question someone of her caliber but it did spawn some questions in my mind. Like, if a planet like Jupiter somehow got flung out of the solar system into the empty space and became a rouge planet, would its moons still continue to orbit it?
And, in empty space away from any star, could those moons generate enough heat through tidal heating (for example) to allow life to form? Or would interstellar radiation outside of the heliosphere prevent that?
If Jupiter became a rogue planet, its moons would still orbit it, although it’s questionable if they would stay in their same orbits during whatever process yanked Jupiter out of its current orbit.
Depending on how it got “flung out of the solar system”, yes; the moons—particularly the inner Galilean moons as well as the Amalthea group moons orbiting most closely—are pretty tightly bound, and it would take an extraordinary event to eject them from Jupiter’s sphere of influence (SOI). How rogue planets are ejected from the systems they developed in is not well understood since we’ve never observed this happening, but certainly with large Jovian-sized planets it is assumed to be a gradual process where the planet (and its associated moon system) migrates outward and then gets into some kind of positive resonance where it ends up decoupling from the system, or else is in a tug of war between two or more members of a multi-stellar system where the planet ends up being drawn out into a long ellipse that converts into a parabola and escapes.
Sure, and in fact in the view of an increasing number of astrobiologists the liquid environment under the protective ice ‘crust’ might be more amenable to the development of life than the unprotected environment of an ‘Earth-like’ planet. Ice (water or otherwise) could provide protection from excessive cosmic and stellar charged particle radiation, and tidal heating and/or interior radioactive decay could provide the energy gradient for life-like systems to evolve and develop, albeit in a way that would be nothing like the evolution of modern life on Earth.
And of course, rogue planets might not be flung out of systems at all. They might have just formed in isolation, the same way that stars do but on a smaller scale.
I’ll suggest that Jupiter’s moon Europa provides a rough analogy with the rogue planet posited in the OP. While Europa is still under the sun’s thermal influence, at its vast distance the sun does essentially nothing to support the necessities of viable life – the warmest temperature at the equator is about -160°C, and -210°C at the poles. Yet due to heat from tidal flexing, it’s believed to have a liquid water ocean under a thick ice surface just as hypothesized for a rogue planet, which might harbour life. Interestingly, both oxygen and CO2 have been detected in Europa’s thin atmosphere. Another point is that besides tidal flexing, a rogue planet might have subsurface heat from residual heat in its core and from radioactive decay and maybe even fusion processes.
That might be true for super-Jovian planets up to brown dwarfs (which are essentially ‘failed’ stars that could not sustain conditions for p-p fusion in their cores) but not for the smaller ‘icy giants’ like Uranus or Neptune, and almost certainly not rocky worlds on their own. Of course, planets like these could form around a brown dwarf or protostar, but then they aren’t really ‘rogue’ planets so much as they are just planets in a system in which the central mass can’t or hasn’t yet achieved fusion conditions.
Just to be clear, oxygen is produced on Europa by dissociation due to charged particles being produced in Jupiter’s ionosphere. It’s not an indication of life itself, although the oxygen that migrates through the ice might provide an oxidizer to power a native metabolism.
The residual heat from formation and contraction isn’t going to sustain heating on a rocky planet for more than a few million years; radioactive decay (which occurs within Earth’s mantle) could provide heating through vents or to subsurface life but would be rapidly lost to the ambient cosmic background once it reached the surface. There is no possibility of any significant yield from nuclear fusion from a roccky planet or anything smaller than a brown dwarf, and even that cannot produce enough fusion to radiate a significant amount of energy to its gaseous surface.
A rogue planet would have to acquire water (or whatever liquid comprises the oceans) and then produce enough internal heating to keep them liquid over spans of hundreds of millions of years for life to develop. Without a source of tidal heating this is unlikely to say the least.
Life, to originate or be sustained, requires not just energy but an energy gradient. Would tidal heating provide a gradient that organic molecules could access? It seems to me that tidal flexing would heat the moon rather diffusely throughout its bulk.
No, but liquid oceans can only be sustained in that state with some significant amount heat input that equals or exceeds that radiated out to space, and there is no way for radioactive decay to produce enough interior heat flux to maintain surface oceans over hundreds of millions of years.
Tidal heating keeps the ocean’s of Jupiter’s moons Europa and Ganymede liquid, and the same is almost certainly true for Saturn’s moon Enceladus (thanks to its resonance with Dione). The tidal heating also drives the volcanism of Jupiter’s moon Io, so it is clearly capable of creating a substantial amount of internal ‘frictional’ energy that then migrates outward, creating a gradient and driving geochemical and transport processes. Whether there are natural chemotrophs on any of those moons that can utilize those gradients to drive non-equilibrium thermodynamic processes is still unknown but there are definitely energy gradients and active geochemical interactions which could offer the potential for life-like systems.
Here’s a brief lecture from one of my favorite geochemist communicators:
I understand that the geothermal vents would not be sufficient to keep the global oceans liquid but I think they could manage several hundred meters around where they exist and, if you look at something like the mid-Atlantic ridge, that’d still be a pretty big area.
Not picking on you, but several folks including you have sorta blurred the distinction between the rogue planet itself and its various moons.
Something similar to a rogue Jupiter could certainly create enough tidal heating amongst its satellite(s) to support such under-ice oceans on the satellite(s).
But not on the primary rogue itself.
Which is interesting in that the rogue primary operates as a “sun” to its seconadaries, but provides its energy input to its satellites in the form of gravitation, not photons.
It’s unclear to me how that would work on something more like the Earth-Moon system where compared to most other systems, the secondary is an appreciable fraction of the primary’s mass, and orbits close for that mass.
For sure both bodies are “kneading” the other, but is it enough? Absent Sol’s input, Earth might still have black smokers driven by residual heat of formation + radioactive decay + tidal kneading. But it would also have an ocean of solid ice except for comparatively teeny upside-down puddles of liquid surrounding each smoker.
A binary planet (imagine a closely coupled Venus + Earth system) would have even stronger mutual kneading if close enough together. Not sure about the longevity of that situation. Kneading isn’t free; it’s paid from reductions in orbital momentum. Leading to slower orbits farther out. Could an aggressively kneading close binary last long enough to form life? Not my area of expertise, but fun to think about.
Yes, this is the most likely scenario. A rogue Jupiter-like planet could support life on several of its moons thanks to tidal heating, assuming that life can start on such worlds in the first place. But the Jupiter-like planet itself would probably not support life, unless microbiota were transferred from the moons to the planet via cryovolcanism.
I suspect that’s the problem. Although we don’t yet know all the factors required for abiogenesis, it may be the case that underwater hydrothermal vents are non-starters, literally. Even on Earth, do those extremophiles not still rely on the deposition of organic matter from the surrounding ocean for sustenance?
The world’s best experts cannot agree on where they think the best place for life to have originated - vents or ponds. To a (well read) layperson like myself, underwater hydrothermal vents are popular because they are the theory de jour. There are many strikes against them, saltwater being one of the main ones. I’m always amused when I hear experts talking about vents and the Miller-Urey experiment in essentially one breath.
I think extremophiles need to be left out the equation. They have had billions of years to evolve into those conditions. Just because an organism can live in an extreme environment now doesn’t mean they could have originated in those environments.
