Why does humanity live on a planet orbiting a rare G-type dwarf star (like our Sun) when M-type red dwarfs comprise 82% of stars and are 33 times more abundant?
Why do we live so early (1% into) the Stelliferous era, when long-lived M-dwarfs will dominate for trillions of years, far outlasting G-dwarfs’ 10-billion-year lifespans?
These form the Red Sky Paradox suggesting something suspicious about M-dwarfs despite their frequent rocky planets in habitable zones.
CoolWorlds uses Bayesian modeling and simulations of 1 million stars over cosmic history. He uses star formation rates which will peaked at cosmic noon ~10 billion years ago, stellar lifetimes, and the initial mass function (IMF).
We will look at the odds of
pure luck (low probability),
the desolate M-dwarf scenario (low-mass stars < ~0.5 solar masses inhospitable to observers due to factors like prolonged high-energy radiation stripping planetary atmospheres) and
a truncated window (finite ~10-billion-year habitability due to e.g., failing plate tectonics).
The Bayesian results favor the desolate M-dwarf hypothesis (Bayes factor ~1,600:1 against luck and ~1,000:1 over truncated window alone).
This yields a ~95% confidence cutoff at 0.34 solar masses—excluding ~67% of stars from hosting intelligent life. This aligns with geophysics (Earth's tectonics ~10 billion years) and JWST observations (barren Trappist-1 planets). It implies a solar-like sweet spot for complexity, resolves the Fermi paradox (fewer civilizations), and predicts quiet M-dwarf systems barring colonization. A radical "grabby aliens" idea fares worse.
Formulation & Resolutions of the Red Sky Paradox by David Kipping, 2021
There is work suggesting Planets only have active plate tectonics for 10 billion years.
There is evidence that going below 0.34 solar masses causes problems for allowing life.
The early billion years or so of red dwarfs have a lot of excess radiation that is problematic for life.
We need to increase observations support what Bayesian statistics is suggesting red dwarfs (low mass stars) make it difficult to support life.
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Lots of things can prevent technological life developing. No coal beds means no industrial revolution, for example.
One cannot deduce trends from just one data point.
We need more hi-res observations before any of these questions can be answered.
Interesting play with numbers though…
I think an important issue to consider is that while stars can have very different types of emission (from superhot blue stars to dim brown dwarfs one) not all the photon emissions are suitable to be converted into chemical energies through photosyntesis: infrared might warm you up or coock you, but generally has not enough energy to form new chemical bonds, while ultraviolet or even more eneergetic photons like x rays break up complex molecules.
Without photosynthesis, the chemical energy available for organic life is not renewed, and it all gets consumed into the food chain and ultimately converted into entropy. You need photosynthesis to have long-lasting life on a planet and photosynthesis works only woithin a certain photon energy range, therfore requires a certain tupe of stars
I used to think there were alien microbes out there, but now that I know what it takes to create even the simplest possible self-replicating cell, I don’t think so. I think we’re probably alone in the universe, at least in the physical plane.
The question and conclusion
“Why are we around a G-type star so early in the age of the universe? Must be because life is only possible within 1% of the Stelliferous age.”
sounds like
“Why are we alive right now and not in the future when the population will be in the quintillions in the solar system along once we build trillions of O’Neill colonies? Must be because humanity will go extinct in our lifetime.”
If Plato asked this question 2500 years ago, would have been right to conclude that his generation would be the last generation of humanity?!? The answer is obvious so why should we think the same about the odds that life would arise at this point in time and at this location? It has to start at some point in time at some place and that the question if asked at a different point in space-time would be indistinguishable from asking about it now.
It’s okay to ask if M-type stars could ever host habitable planets based on measurable properties. Would the violent flaring and intense solar winds that are often seen in M-type stars destroy the atmosphere of planets in the Goldilock zone? Would an atmosphere be protected if the planet was an Earth-size moon orbiting inside the magnetosphere of a gas giant like Jupiter? But thinking that there’s something special about the point of space-time you occupy when you could ask the same question about a different point in space-time and still come up with a similar conjecture.
Alternatively, we could also conclude that 1) someone would have to be born in this time so why not us and 2) the reason why we live during a time within 1% of the Stelliferous Age is because the universe has only existed for about 1% of the Stelliferous Age.
As an example, the universe just isn’t old enough for intelligent life to arise on a planet orbiting a particular star 50 billion years from now. Just wait another 50 billion years for the universe to be 63.8 billion years ago, and there should be an alien civilization there.
The possibility that there’s life on moons is very strong, maybe cumulatively as strong as there being life on planets, because there are so many more of them. Yet, it’s not in famous Drake equation, nor in most exobiologists’ calculations. Our solar system alone contains multiple possibilities for moon life in the outer planets, and having large outer planets is no longer considered especially “normal;” there are plenty of observed Jupiter sized worlds circling their stars in the Goldilocks zone – a measurement itself which should be challenged if a moon’s planet is large and close enough to provide tidal heating. This seems to be the presumption in the movie series Avatar (as well as in my newly remastered 40-year old illustrated book: Impland: An Alien Utopia, available on Amazon). Including the possibility of moon life then, might double the chances of life per star.
For an earlier take on this: https://www.amazon.com/Rare-Earth-Complex-Uncommon-Universe/dp/0387952896/
It’s worth noting that, just because a planet has a history that wasn’t suited for life arising and becoming complex in the first place, doesn’t mean that it wouldn’t be suitable for a technological species to terraform and colonize.
This, along with eukaryogenesis being rare, both suggests we are alone at least within our local cluster of galaxies. Aliens no doubt exist. But the nearest ones are likely a billion light years from here.
Eukaryogenesis (or its equivalents) isn’t necessarily rare, but it was tied to the singular Great Oxidation Event, which likely acted both as enabler and limiter, and can normally occur only once per planet. Once a successful eukaryote has developed, it would also have an overwhelming competitive advantage against any potential runner-ups.
Specifically the endosymbisos step occurred multiple times on Earth: with mitochondria, plant chloroplasts, amoebic chromatophores, and nitroplasts in at least two separate lines of algae. And the precursors to the nucleus and other eukaryotic cellular structures were already present in prokaryotes, as evidenced by cyanobacteria’s thylakoids and mitochondrial cristae. The genetic mechanisms for such structures were likely spread through horizontal gene transfer.
The key co-evolution factor and limiter was likely the GOE. Those early cellular structures likely predate the evolution of photosythesis in cyanobacteria, and were refined into thylakoids during the GOE. They would also be useful for the aerobic ancestors of mitochodria, later evolving into their cristae. Crucially, those aerobic ancestors couldn’t have evolved before there was oxygen available.
The oxidative stress from the GOE could push those early cellular structures to evolve into early nuclei precursors, to protect the DNA. Once mitochondial endosymbisos occurred, their byproducts would further push the oxidative stress, promoting more mature nuclei to evolve.
All of this likely occurred in multiple lines in parallel, but once a successful line emerged, it had an overwhelming advantage in its metabolism and cellular machinery.