Life Without Stars: Stanets and Ploons
The implications of an important 2023 paper have not been fully understood: it is possible most life in our universe is in the deep oceans of icy moons, orbiting planets that do not orbit stars
Note: I've been fiddling about with this post for a year. It started out short. I was young, and full of hope and dreams. Two false starts and fifteen drafts later, it is now long. I am no longer young and full of dreams. Yes, I need a more efficient writing system. Someone apparently posted a paper on a similar topic recently (which I can’t track down, aaargh, should have taken a note when I saw it mentioned, yes I also need a more efficient filing system), and so I've been jolted into finally finishing mine. Anyway, I think life without stars – and potentially lots of it –is a big deal. Hope you find this as interesting as I do.
Last year, the James Webb Space Telescope made a startling new discovery about how, and where, planets can form. In a nearby star-making region, it spotted a bunch of recently-formed, roughly-Jupiter-sized planets, still warm from their formation, that weren’t attached to – weren’t orbiting – stars. A surprisingly large number of those Jupiter-sized planets were in binaries, with two Jupiters orbiting each other – but, again, with no star involved. (See the fascinating paper, Jupiter Mass Binary Objects in the Trapezium Cluster, by Samuel G Pearson and Mark J McCaughrean.)
The discovery of so many standalone planets implies that most of the life in our universe may not be on planets orbiting stars. But the implication isn’t immediately obvious from the study, and so doesn’t seem to have been fully appreciated yet. (If I’m wrong, and someone has been making this point elsewhere, please send me a link and I’ll credit them.) So let me walk you through the logic here…
IS THERE LIFE ON MAAAAAAAAAARS?
Let's think about where we are most likely to find life in our universe. We may as well start with the only life we have direct knowledge of: our own.
We are alive. (Hurray!)
How come?
Well, we live on a rocky planet, with a liquid water ocean exposed on its surface.
All life on Earth came from that ocean. (Because liquid water facilitates all the chemistry of life.)
The ocean stays liquid, and life stays alive, thanks to a constant flow of highly energetic sunlight from the star our planet orbits.
Because those three things seem pretty fundamental to life on Earth, we have historically tended to assume that life elsewhere in the universe would also be found on planets very similar to Earth.
But, if you look around our solar system, it contains several other rocky planets, also orbiting our sun, and none of them have been able to hang onto a liquid water ocean – or, as far as we can tell, develop complex life. Let’s take a quick look at all four rocky planets, in order of distance from the sun, and see how they are doing after 5 billion years.
Mercury (between 46 and 70 million kilometers from the sun – yeah, that’s a pretty eccentric orbit): Too darn hot. Everything just boiled away into space. It doesn't even have an atmosphere anymore. It’s hot enough to melt metals like tin and lead, great. And it’s so close to the sun that its rotation has been slowed, so that a single day (sunrise to sunrise) now lasts for roughly a hundred and seventy-six Earth days – and the daytime temperature reaches 430°C (or 800°F, or 703 K). But don’t worry, you can cool down during the six-month-long nights, when it drops to minus 180°C (or -290°F, or 93 K). Yuk.
Venus (roughly 108 million kilometers from the sun): Too hot. Seems to have generated way too much carbon dioxide (96% of its, extremely thick, atmosphere). It therefore cooked itself, through a runaway greenhouse effect (all that CO2 trapping the sun’s heat), which boiled any water it might have had. It now rains sulphuric acid instead. But hey, you’re in luck! It’s even hotter than Mercury, reaching 465°C (or 869°F, or 738 K) – so the sulphuric acid raindrops evaporate before they reach the ground!
Earth (roughly 150 million kilometers from the sun): Neither too hot, not too cold! Like baby bear’s porridge! We’re doing great! Liquid water oceans, and so life is partying hard pretty much everywhere. (Some big deserts, and frozen at the poles, but you can’t have everything.)
Mars (between roughly 207 and 249 million kilometers from the sun –yeah, eccentric orbit): Too darn cold. Used to have liquid water oceans, but they dried out over a billion years ago, and most of its atmosphere has since blown away, along with much of the evaporated water. Now it’s cold and desolate, with an occasional thin layer of white carbon-dioxide frost at the poles, in a sad parody of a planet with a real water cycle. Maybe Mars has some microbes living in the remaining water, deep under its radiation-blasted surface, but that’s it.
So, from an evolved-universe point of view, it doesn't really look as though the basic parameters of matter have been optimised by evolution to create the conditions for life on the exposed surfaces of rocky planets. Rocky planets have to be in quite a tight Goldilocks zone – not too hot, not too cold – and they have to get lucky. (Even lucky old Earth has had several mass extinction events, when asteroids hit its exposed surface ocean. The dinosaurs, most famously, were taken out globally, 65 million years ago, by a single rock the size of Mount Everest hitting the Gulf of Mexico.)
But our theory argues that intelligent, technology-wielding life in a universe helps that universe reproduce. (See this for more details, if you’re new here.) So, if biological life is evolutionarily beneficial to universes (if it helps the universe itself to reproduce), then over many generations of universe, evolution should have optimised universes for the production of life. The conditions for life should therefore be common and stable, not rare and unstable, as they seem to be on the surfaces of rocky planets.
So… Is there somewhere else in our solar system (and, by extension, our universe) where the conditions for life are common, and stable? Let's think about that.
(TAKE A QUICK ZOOM-INTO-THE-MOONS BREAK)
(Substack, very sensibly, compresses monster images like the one above – most people most of the time do not want to look at a 15 megabyte image on their phone – so unfortunately you can’t zoom in, and see the full glory here. I recommend you instead click on this link to the fabulous 15 megabyte original, zoom into that, and explore for a while. It will give you a terrific crash course in the moons of our solar system.)
BACK TO BASICS
Another way to think about where we might find life, then, is to think about the absolute basics that would be required. Not the specifics, the basics.
They seem to be:
A liquid water ocean
A source of heat
A source of nutrients
When we look around our own solar system with those three things in mind, the most likely places to find life turn out not to be small rocky planets with surface water oceans heated by the sun.
Instead we come up with the icy moons of Saturn and Jupiter (and of Neptune and Uranus, but we have sent a single, less sophisticated probe to them – Voyager 2 – less recently – it launched 1977 – so we have less data). There are a lot of icy moons in our solar system, and a large number seem to have substantial liquid water oceans. (Jupiter’s moon Europa is only the size of our own moon, yet it has a liquid water ocean twice the volume of all the water on Earth.)
How can all this liquid water be? After all, these moons are much further away from the sun than the earth is (or Mercury; or Venus; or Mars), and these lunar surfaces are therefore frozen. Not just frozen, but deep frozen: Europa is minus 150°C (or -238°F, or 123 K) in the daytime (and colder again at night).
WHO LOVES THE SUN? NOT JUST ANYONE…
And, indeed, as it turns out, the sun has basically nothing to do with it.
These liquid water oceans lie deep beneath the frozen surface of the icy moons. They are kept liquid by heat from their molten rocky cores. Those cores are kept molten, in turn, by gravitational friction, as the moons orbit Saturn or Jupiter (or Uranus or Neptune) in slightly eccentric orbits.
A TIDE INSIDE THE MOON: GRAVITATIONAL FRICTION
How does that work? Well, as the moon moves closer to, then further from, the planet with every orbit, the centre of the icy moon is tugged on harder, then softer, by the planet’s enormous gravity. It generates tides inside the moon.
This gravitational back-and-forth friction steadily transmits gravitational energy from the enormous planet to the far smaller moon. And friction means heat. That heat melts the rocky core of the moon (a core which is already being heated by the pressure of all the weight above it). And it melts the lighter ice above the core. As this process is going on constantly – as heat is being generated in the core by gravitational friction with every orbit – the ocean stays liquid, all around the moon, in a zone that can be hundreds of miles deep. (The deepest the oceans get on earth is only seven miles.)
EFFICIENCY: ELECTRIC KETTLE VERSUS DISTANT BURNING WAREHOUSE
This is an extremely efficient way to keep water liquid, compared to the extremely inefficient method for keeping Earth’s oceans liquid. Earth has to have an entire star pump crazy amounts of energy out in all directions – covering the entire sphere of mostly empty space around it, and cooking the planets nearest it – in order to have 0.000000045% of that light (so, less than a billionth) fall on the Earth, keeping our oceans from freezing. (And, as these oceans are exposed on the surface, with just a few kilograms of air per square inch insulating them from the chill of space, they would freeze pretty fast without that heat from the sun). Indeed, the oceans at the poles do, in fact, freeze once a year, in the depths of their respective winters.
Put another way, icy moons are like electric kettles: all the energy is used to heat the water.
The exposed surfaces of rocky planets heated by a star, however… Well, it's like using a blazing warehouse a mile away to make a cup of tea.
You can see why the evolution of universes might favour the gravitational friction/electric kettle model, once it's emerged.
So that’s number 1, liquid water oceans, and number 2, heat. Icy moons beat rocky planets on both counts. Much more water, much more efficiently heated.
What about number 3, nutrients?
NUTRIENTS
Well, we recently discovered that the liquid water oceans on the icy moons of Jupiter and Saturn seem to contain all the nutrients necessary for life, too. (I wrote about it here.) As on earth, hot vents on the ocean floor pump carbon, sulphur, phosphorus, etc., up from the molten core and into the ocean. The bottleneck nutrient was phosphorus: it tends to get trapped in rocks, and not be available for life. But we've managed to sample the water that emerges from the ice-volcanos of Enceladus (an icy moon of Saturn), and discovered it is far richer in available phosphorus than even the oceans of Earth. (See the original excellent paper from last year, Detection of phosphates originating from Enceladus’s ocean, by Frank Postberg, Yasuhito Sekine, Fabian Klenner, et al.)
So the molten rocky cores provide both heat and nutrients.
It therefore looks as though the basic parameters of matter in our universe have been optimised by evolution to generate the conditions for life in the liquid water oceans of icy moons, rather than on rocky planets.
NO GOLDILOCKS ZONE REQUIRED
Most moons in the outer (colder) reaches of any solar system are going to be icy (just as most comets are icy) because H2O is the main raw material floating around out there (other than primordial hydrogen), as such moons form. And, crucially, for icy moons, there's no particular Goldilocks zone. Any icy moon orbiting any large gas giant planet will have a liquid water ocean if its orbit is even slightly eccentric – and they usually are pretty eccentric, because that's what the chaos of the formation of a solar system gives you. And, even better, moons tend to slip into resonance with each other, which preserves and keeps stable the eccentricity of their orbits. Ganymede, Europa, and Io, for example, are in 1:2:4 resonance with each other: that is, for every single orbit of Jupiter that Ganymede makes, Europa makes two, and Io makes four. That keeps all three orbits stable, longterm: if one were to drift slightly, the others would gravitationally nudge it back into resonance.
So what we are seeing here is a strong, simple, robust, self-stabilising system that should automatically build out large numbers of potentially habitable worlds in every solar system. Order automatically emerges from randomness, and is automatically maintained. There’s no delicate single-point-of-failure to worry about. No precise, narrow Goldilocks zone you have to stay in.
PROTECTION
And if life does develop on an icy moon, it’s far better protected than on the surface of a rocky planet like Earth. The frozen surface of an icy moon is usually many kilometres thick, and at a temperature so cold that the ice is stronger than ceramic. (Ice gets more brittle, but also harder, the colder it gets.) Thus the oceans beneath are protected from solar flares, cosmic rays, radiation from nearby supernova explosions, and the kind of asteroid event that caused the mass extinction of the dinosaurs.
Oceans under miles of ice are also protected from evaporation into space, which is a big problem on small rocky worlds with low gravity, where the solar wind steadily strips away atmosphere, including evaporated water. That's what fucked Mars. (And of course – even closer, even hotter – Mercury.) But that can’t happen to THESE oceans.
As a result of all this, some great scientists, like Kevin Hand, Carolyn Porco, Chris McKay, Steve Vance, Jonathan Lunine, and Robert Pappalardo, have been arguing for years for a complete rethink on where we should be looking for life. Alan Stern is one of them.
“Oceans are ubiquitous. Most of them are in the outer solar system. And they could be abodes for life. This is a fundamental sea change in the way we view the solar system.”
– Sol Alan Stern, a guy who has done everything, working as an astrophysicist, an engineer, a planetary scientist, and the principal investigator of the New Horizons mission to Pluto.
LIFE WITHOUT STARS
That’s all great. But the situation may be even more extreme than Alan Stern and the others argue. As I mentioned up front, a recent discovery indicates that evolution may have selected very hard indeed for life in the liquid water oceans of icy moons. So hard that we may not need stars at all for life to evolve there.
Now, obviously, we still need stars to make all the elements (by fusion, in their core) and distribute them (by supernova explosion), so there can be planets in the first place.
But, once that is done, the model we are so familiar with – a star orbited by a planet, and that planet orbited by a moon – may not be the dominant model in our universe.
Here’s the abstract from Jupiter Mass Binary Objects in the Trapezium Cluster, by Samuel G Pearson and Mark J McCaughrean. (I’ll expand on its implications below)…
ABSTRACT
“A key outstanding question in star and planet formation is how far the initial mass function of stars and sub-stellar objects extends, and whether or not there is a cutoff at the very lowest masses. Isolated objects in the planetary-mass domain below 13 Jupiter masses, where not even deuterium can fuse, are very challenging to observe as these objects are inherently faint. Nearby star-forming regions provide the best opportunity to search for them though: while they are young, they are still relatively warm and luminous at infrared wavelengths. Previous surveys have discovered a handful of such sources down to 3–5 Jupiter masses, around the minimum mass limit established for formation via the fragmentation of molecular clouds, but does the mass function extend further? In a new James Webb Space Telescope near-infrared survey of the inner Orion Nebula and Trapezium Cluster, we have discovered and characterised a sample of 540 planetary-mass candidates with masses down to 0.6 Jupiter masses, demonstrating that there is indeed no sharp cut-off in the mass function. Furthermore, we find that 9% of the planetary mass objects are in wide binaries, a result that is highly unexpected and which challenges current theories of both star and planet formation.”
–Abstract, Jupiter Mass Binary Objects in the Trapezium Cluster, by Samuel G Pearson and Mark J McCaughrean
This paper has huge implications for where we will find life in the universe, so let me explore them.
WHY THIS IMPLIES LIFE WITHOUT STARS
The traditional assumption was that there were only two ways a planet could form: core accretion, and disk instability. Crucially, both of these were assumed to take place only in the swirling protoplanetary disk of gas and dust around a newly forming star.
Core accretion is the most popular model, with the most observational support. It proposes that an initial small, solid seed of dust and ice slowly grows by collecting (accreting) more material – including, eventually, a thick gas atmosphere, once the core is massive enough to gravitationally attract the gas.
With the disk instability model, a fairly large area of gas and dust in the protoplanetary disk grows unstable, and collapses, to directly form the entire planet in one go. The heavier elements (the dust) quickly settle to form the core, while the gas forms the atmosphere. (This model has less observational support, and, though it may well happen, is currently believed to be roughly an order of magnitude rarer. See PLANETARY FORMATION SCENARIOS REVISITED: CORE-ACCRETION VERSUS DISK INSTABILITY, by Matsuo, T., Shibai, H., Ootsubo, T, and Tamura, M.)
So this new paper goes on to outline how they saw a lot of star formation, as they expected to, and planetary disk formation around those stars, as they expected, and planets condensing out of those planetary disks, as they expected.
But they also saw large numbers of Jupiter-sized planets forming without any star. That is, condensing out of the gas were freestanding Jupiters not orbiting any star, not forming from a planetary disk around a star, just forming in open space. Given the traditional assumptions about planet formation, this was not expected. In fact, that's a severe understatement. This was a huge shock to the astronomers.
They had generally assumed there was a mass cut-off, below which such objects couldn't form, or could only form with difficulty, under unusual conditions (and thus rarely).
What they were now seeing simply didn't fit their model of planetary formation. And these independent, free-standing Jupiters-with-no-star were numerous. This wasn't just an isolated one-off, they found hundreds of them, in a relatively modest region of space. Plus, many of these starless Jupiters formed binaries: that is, two Jupiter-sized planets in orbit about each other. This shouldn’t happen!
“This has not been predicted at all. There are no existing theories where we would have expected these wide, free-floating planetary objects in these numbers.”
–Matthew Bate, head of the Astrophysics Group at the University of Exeter, quoted in Wired
Well, we know that stars often form in binaries (in pairs that orbit each other): so why are astronomers so surprised to find two Jupiters orbiting each other?
Because, yes, sure, massive stars commonly form binaries: but as stars grow smaller, binaries grow less and less common. For really massive stars (some of them 100 times more massive than our sun, and therefore 100,000 times more massive than Jupiter), the vast majority – between 70 and 90% – are in binary or multiple systems.
At the bottom of the scale, the smallest stars are brown dwarves – barely stars at all, as they can’t fuse hydrogen, only small amounts of super-easy-to-fuse deuterium. Thousands of times smaller than the most massive stars, brown dwarves are between just 0.075 times and 0.015 times the mass of our sun (but still between 15 and 75 times more massive than Jupiter) – and only 5 or 10% of the smallest of them form binaries. Also, the two stars in those binaries are usually really close together. So these Jupiter-sized planets, being far smaller than even the smallest stars, should be forming almost no binaries at all. Yet 9% of them are in binaries! And the two are really widely separated! So a rule that applies over four or five orders of magnitude breaks down once we get to this particular size.
The astronomers call these weird little Jupiter-sized guys by the current standard term, planetary-mass objects, or PMOs (and they christened the ones in binaries JuMBOs – Jupiter-mass binary objects). And they found hundreds of the little feckers, both single and binary, in just a small patch of the very first stellar nursery we've looked at through the new James Webb Space Telescope (the first telescope able to see them). Remember, we can only see the largest and most recently-formed ones, still glowing hot in the infrared, before they cool down. Many, many more such freestanding planets (or, if you are being picky, planetary-mass objects – we will return to this terminology problem later) are presumably also in that region – they've just cooled down too much for us to see, or they are really small.
It's therefore possible that freestanding planets might greatly outnumber planets formed around stars. If that generalizes across all stellar nurseries, and there's no reason to believe it won't, then the vast majority of large planets in our universe (and maybe small planets, too, though that’s less relevant to my argument) exist without stars.
MOST LIFE IN THE UNIVERSE DOES NOT REQUIRE A STAR
If they go on to form icy moons… Well, if life is to be found chiefly in liquid water oceans beneath the surface of these icy moons, and if these icy moons are mostly orbiting planets that are not orbiting stars – then most life in the universe does not require a star. (I haven't seen anyone else point out this implication. But I can't be the first to have seen it, so please tell me if you know of an earlier mention, and I'll credit them here.)
And the bias against star-based life might be even more extreme than the raw number of planets-without-stars suggests.
HILL SPHERE BLUES
That's because the Hill sphere is the area around a planet where moons can be found – because within that sphere, the gravity of the planet is more powerful than that of the star the planet (and its moons) orbit. For Neptune’s Hill sphere, for example, we're talking a radius of one hundred and fifteen million kilometers. (That’s 0.77AU, or 0.77 times the average distance between the Sun and the Earth.) Any moon outside that limit will eventually be pulled free of Neptune by the sun.
But for free-floating planets with no nearby star, the Hill sphere would be much, MUCH larger. Moons could be waaaaay out from the planet, and still be in a stable orbit. Such planets could therefore support more moons, in their larger Hill sphere. (See my BRILLIANT illustration, above. While noting it is extremely simplified and not to scale.)
If this is the case – if most of the life in the universe does not require stars, but is instead in these starless planet-and-moon systems, each with an extra-large helping of moons – then we clearly need new terminology. A freestanding planet that is not orbiting a star, but is instead the gravitational centre of its own system, needs a different descriptive term than a planet orbiting a star. And “planetary-mass object” is
A) Too long
B) Pug-ugly, and
C) Not precise enough (as it can refer to planets, dwarf planets, planetary-mass satellites, free-floating planets ejected from a system, and sub-brown dwarfs).
THESE AREN’T ROGUE PLANETS
The traditional term for a planet that’s not orbiting a star is “rogue planet”; but this assumes the natural condition of a planet is orbiting a star, and to leave it is to “go rogue”: to become a rare outlier. And so “rogue planet” is still a useful term; it works for a planet that formed around a star, but has since been ripped away from it, and hurled into interstellar space – perhaps gravitationally sling-shotted out of its solar system by a larger planet. But “rogue planet” is totally inappropriate for worlds formed with no star to orbit in the first place. (Indeed, if most worlds are formed independent of any star, then it’s places like Earth, Mars, Jupiter, and Saturn that are the oddities, the outliers.) So we need new terms.
STANETS
I suggest we call these planets, formed independently of any star, “Stanets” – short for star-like planets. Star-like planets in that they are at the centre of a system, not orbiting it. If our sun is the centre of our solar system, and a star is the centre of a stellar system, and a planet is the centre of a planetary system (with the star which that system orbits offstage, but implied) – then stanets are the centre of a stanetary system.
PLOONS
And of course we also need another term for the moons (many of them icy) that orbit these star-like planets.
I suggest “ploons”; planet-like moons, because these moons essentially are the planets orbiting the central Jupiter-sized object.
So, much of life in our universe may exist without stars! It is found on “ploons” orbiting “stanets” – on planet-like moons orbiting star-like planets – in the dark spaces between the larger, less numerous, luminous stars.
BACK TO AN EVOLUTIONARY THEORY OF UNIVERSES
Let’s ground all this in the evolutionary theory of universes we are exploring here on The Egg and the Rock, where universes reproduce through black holes.
The three-stage model of cosmological natural selection argues that our universe has three stages of reproduction:
First, through an initial wave of direct-collapse supermassive black holes. Those supermassive black holes then dynamically generate galaxies of stars, as I’ve outlined here.
Those stars generate a second stage of reproductive success, by forming black holes at the end of their lives.
But the third wave of reproductive success is the largest, and it comes when intelligent lifeforms wield technologies to manufacture artificially small black holes (for maximally efficient energy production). More life = more black holes = more reproductive success for that universe.
Maximizing the production and distribution of life in our universe is therefore maximizing the reproductive success of the universe as a whole.
It is quite possible that exposed surface water oceans on rocky planets were once – in the evolutionary past, many generations of universe ago – the original way in which life was generated. The intelligent life which developed on those rocky planets ultimately optimised its energy production by building small technological black holes, which meant reproductive success for the universe as a whole.
But you can only get a tiny number of planets to generate life that way per star – that's a very, very small number of life-bearing worlds for a given mass. This is because most of the mass is caught up in the star, which can only produce (eventually, at the end of its life), a single (wastefully large) black hole.
Multiple icy moons would be more successful around planets orbiting stars – you're getting a lot more life and thus a lot more small black holes for the same amount of matter. But you’ve still got most of the mass of the system locked up in a star.
But once you're able to make large numbers of Jupiter-sized planets, efficiently delivering gravitational energy to large numbers of icy moons forming liquid water oceans – and those planets are no longer limited to roughly two or three per star – you get runaway reproductive success, a huge evolutionary breakthrough which would be conserved. A star’s worth of gas can instead make hundreds of free-standing Jupiters. Rather than one star, you get hundreds of stanets, and thousands of life-bearing ploons.
So our universe may be part of a slow evolutionary transition from universes where life was commonly produced on the surface of rocky worlds, to universes where life is more commonly produced in the liquid water oceans of icy moons, orbiting planets that may not even be orbiting stars.
You can see this as simply the latest stage in the long evolutionary history of universes, where, at each step, simple Darwinian evolution selects for those universes which produce the largest number of black holes (and thus offspring) per unit mass.
Remember, smaller black holes don't mean smaller offspring: in our universe, the positive mass energy and the negative gravitational energy net out to zero. You could build our universe out of, essentially, nothing. So a black hole, no matter how small, can generate a full-size universe.
THE LOGIC OF EVOLUTION MOVES UNIVERSES TOWARDS STANETS AND PLOONS
At stage one, the universe is maxing out on simple direct-collapse supermassive black holes.
But once you have the breakthrough to stage two (universes capable of making both direct-collapse supermassive black holes, AND smaller stellar-collapse black holes), it makes evolutionary sense to use less mass making the supermassive black holes, and reserve more mass for making stars, and thus (smaller, and far more numerous) stellar-mass black holes. Overall, you are making way more black holes per unit of mass, and thus are more reproductively successful.
And once you have the breakthrough into stage three (universes capable of making direct-collapse supermassive black holes, AND smaller stellar-collapse black holes, AND much smaller technologically-produced black holes), it makes evolutionary sense to use less mass making stars, and reserve more mass for making free-standing planets and their icy moons – stanets and ploons. You get less stellar mass black holes, but WAY more technologically-produced small black holes.
In other words, at stage three, you are no longer maximising stars, or even solar systems with planets; you are maximising the number of environments in which intelligent technology-wielding life can evolve. And that’s stanets and their life-friendly ploons.
So my prediction is that stanets and ploons will turn out to vastly outnumber – by at least an order of magnitude, and probably much more – the normal planets-and-their-moons orbiting stars.
Exciting times!
SOME FINAL THOUGHTS
An evolved universe, with the basic parameters of matter fine-tuned by that evolution to generate conditions suitable for life, doesn't mean you will find life in all these liquid water oceans on all these icy moons, and ploons. Evolution is a messy business, as my grumpy friend the biologist Yogi Jaeger constantly reminds me. And evolved life is exuberant, excessive, wasteful. Most seeds do not become plants; most plants do not make it to their maximum size. Most liquid water oceans will not generate intelligent life. But enough of them will.
Our evolved universe will never resemble a row of perfectly tended plants. It will be more like an unkempt grove of trees and bushes and weeds. Some plants will thrive, some wither. Some will have enough heat, and shade, and water, and nutrients, some too much, or too little. But overall, even though at any given moment half of the trees, the bushes, the weeds are dead or dying, the grove as a whole will thrive; life will thrive.
CIVILIZATIONS THAT CANNOT LOOK UP AT THE STARS
Icy moons may also provide a partial answer to the Fermi paradox (“If there are aliens… where are they?”) They are under the ice, evolving away far more slowly than us, at far lower temperatures, but in far greater safety. But their sheltered development raises an interesting possibility.
Humans have been tormented by the idea of a larger universe from day one. Just look straight up, and you will see either the sun, or the moon, stars and planets. More than that: Shooting stars! Comets! Supernovas! (OK, supernovae!) We may not have had any idea what they were, or how far away, but we knew there was a lot going on, and we have always dreamed of going out there: exploring.
An advanced civilisation that developed in a single, vast, subsurface ocean, beneath a crust of ice twenty or fifty or a hundred miles thick, may never even conceptualise a larger universe – an elsewhere – let alone explore it.
But that’s moving into the realm of speculative philosophy. Another post, for another day.
WATER, WATER, EVERYWHERE
I can't end this without shifting focus one more level. Everything we've talked about here is dependent on one strange fact that we are so used to, we have stopped seeing it as odd: water expands when it freezes. This is true of very, very few substances in nature. Plus, those few are (apart from silicon) usually rare (germanium, antimony), and usually don’t expand by much, maybe 3%. Water expands a LOT, by 9%, when it turns to ice. Ice is therefore much lighter than water; ice floats. Liquid water thus freezes from the top down – yeah, even though warm water rises. It’s very, very, very odd behaviour for a liquid, and it makes life possible here on Earth, but also on those icy moons.
Instead, when things get cold – too cold for water-based life – a layer moves into place, on the surface of the water, to protect the life deep within it from that cold. To protect the water itself from the loss of more heat. If it didn't expand – if it contracted on freezing, like the vast majority of substances – ponds, lakes, oceans, and icy moons would all freeze from the bottom up, and everything would die.
The liquid oceans on the moons of Saturn and Jupiter (and an incalculable number of ploons orbiting stanets), are only possible because the basic parameters of matter are fine-tuned such that the two hydrogens and an oxygen that form liquid water take up more space, not less, when they stop randomly wandering about, and lock into the stable lattice of ice.
Mainstream science can describe what happens extremely well – but it can't explain why it happens, because the question is meaningless in a one-shot universe with random, arbitrary qualities. Even though that fact is so immensely consequential. Even though that single unlikely fact unlocks all the possibilities of life.
It's worth pondering why chemistry does that. Why water does that. Why our universe does that.
Which leads to my last thought:
HOW DID I GET HERE?
Think about which is more likely: that all this shit just happened once, out of nowhere, 13.8 billion years ago, by mistake – and everything just happened to arbitrarily and accidentally interlock in such a way that stars, galaxies, planets, life, intelligence, and technology all emerged one after the other, wow, what a surprise, what are the odds, hey? Or that our specific universe, bound inside its little bubble of expanding spacetime, came about, step-by-step, generation by generation, through the only mechanism we know of that can lead from an initial membrane-bound system of utter simplicity to a later, different, membrane-bound system of unfathomable complexity (given enough time and enough iterations, enough generations). That mechanism is (Darwinian) evolution.
OK, feel free to share this post with anyone you think would enjoy it. That really helps spread these fascinating, underappreciated ideas.
If you want to read more about the theory of cosmological natural selection, here’s a link to a good history of the idea, and here's a link to my take on it.
If you want to read about my recent extension of the theory so that it makes predictions, here’s another link.
If you're interested in icy moons, and the recent discovery of phosphorus on Enceladus, here is a link.
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Oh, and have a great 2025.
Comments welcome…
Powerful stuff, Julian!
I suggest that there is a further line of thought indicated here: what are the necessary and sufficient conditions for the kind of life that can expand beyond its world of origin?
It seems to me that this requires the (probably rare) star-and-open-ocean origin (needs a catchy phrase for a name).
Life confined to water without a gaseous atmosphere won't develop mastery of fire or of electricity, at least in any scenario *I* can imagine. Without those, it won't develop mining, metallurgy, advanced tools, or spacecraft.
Also, how does such life further the evolution of the universe?
I am sure that many of us would welcome a future essay exploring this!
Best,
Jonathan
PS--If of interest, you might want to also explore the emergent DMT-verse; a domain in which PhD level researchers are now expressing confidence that there are repeatedly accessible dimensions with specific attributes. If correct, this would be yet another aspect of the evolving universe.
Awesome post, Julian! Two thoughts/ questions about the Hill sphere and tidal forces...
1. The hill sphere for free planets is much larger than for captive planets, but are there other limits on how far out a moon can be and still experiencel forces from eccentricity enough to create oceans? I guess it depends on the eccentricity more than the distance... My thinking is just that the hill sphere isn't quite the whole story re how many ocean bearing ploons you'd expect to find. (I guess the gravity of the ploons themselves could also help hear each other up? But not much, I'd have thought)
2. If you have a ploon orbiting a binary stannet, presumably the double-tidal forces there are even more effective at generating heat than around a single stannet? On the other hand, forming stable ploon orbits seems likely to be much harder around double stannets. I guess it doesn't matter for the theory as a whole but I wonder if you think that binary stannets would be over represented or under represented as hosts of ocean bearing ploons.
(Written on my phone, sorry for phone artifacts)