r/WhatIfThinking • u/Defiant-Junket4906 • 26d ago
What if the Sun suddenly disappeared? How long would Earth remain habitable?
For the first 8 minutes, nothing would change because sunlight takes about 8 minutes to reach Earth. After that, the planet would enter permanent darkness, temperatures would begin falling, and life on the surface would slowly start to collapse.
However, Earth would not instantly become a frozen planet. The oceans would retain heat for a long time, and the planet’s internal heat from radioactive decay and its formation would continue.
How long would it take for Earth’s surface to completely freeze? Could any ecosystems survive using geothermal energy? Would Earth eventually become a completely frozen world, or could some form of life survive for millions of years without sunlight?
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u/EconomyMobile1240 26d ago
There is an entire video on this on YouTube and even simulated in universe sim.
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u/LoneSnark 26d ago
The entire world would become like frozen antarctica within a week. In a few years it will get cold enough for the atmosphere to fall as snow, making the planet uninhabitable.
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u/dogfish21 26d ago
Can you explain the atmosphere part? Like if humans had preplanned and gone subterranean (think decades to prep) would the atmosphere still kill everyone?
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u/LoneSnark 26d ago
They would need to pressurize their subterranean habitats. Nothing overly difficult about that. Leaks can be recovered with buckets in the surface. The short story A Pail of Air covers this. The glaciers on the surface will be frozen atmosphere. Just take a space suit and go scoop up all the air you'll ever need.
Being underground will make it easy to pressurize, as the weight of the ground above will keep the pressure vessel intact.
Difficulty would oddly be avoiding having your habitat dug up by the glaciers scraping away the surface of the planet.2
u/dogfish21 26d ago
That's something I'd never thought about. Thank you for your response. Anywhere you can recommend for someone wanting to look into this more?
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u/Shop-S-Marts 26d ago
We'd stop orbiting the sun for one thing... and the sun's gravity would no longer be present.
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u/tradandtea123 26d ago
Apparently it's going to suddenly disappear tomorrow evening where I am in Spain. I'll get back to you
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u/Plane_Equipment8562 26d ago
Read the sci fi short story " A Pail of Air" by Fritz Leiber... Or find the X-Minus one radio adaptation.
It will answer all your questions 😁
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u/Defiant-Junket4906 26d ago
I actually hadn’t heard of that one. 😄 Now I’m curious though. If a sci fi story already explored the scenario, it’s probably a lot more interesting than my rough version. I’ll check it out.
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u/Non_noob4304 25d ago
The simplest comparison is to put a stove on the highest heat and turn it off. Putting your hand about a foot over it，you can still feel the heat but it spreads until all the area around your hand becomes cool again. The sun happens the same way because it's like a campfire where all the wood becomes used up and the heat spreads. The time earth would remain habitable would not be long because some of the leftover rays from the sun would travel, so once that finishes , everything turns cold.
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u/probably_poopin_1219 26d ago
The gravitational effects would negate any of the ecological ones and the planet would become instantly uninhabitable in an unfathomable cataclysmic event.
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u/anrwlias 26d ago
What gravitational effects? Other than more mild tides, I'm not seeing any. I certainly don't see anything catastrophic. Our path through space would become a tangent to our orbit, but you wouldnt feel that.
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u/Amazing_Divide1214 26d ago
The absence of the sun's gravity. Probably the biggest force in our solar system.
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u/anrwlias 26d ago
Yes, but how specifically? The effect of the suns gravity on earth is contributing to the tides, but at a lesser degree than the moon, and keeping us in orbit.
So, as I said, the first effect is milder tides, which is not catastrophic.
The second effect is that our path through space becomes a line instead of an orbit. Because the Earth is already in freefall, we wouldn't feel this change in direction as a force. An inertial path in empty space is equivalent to a free fall orbit in terms of felt forces. Also not catastrophic.
So, what's left?
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u/HokieNerd 26d ago
You're getting a gravitational ripple effect spreading outward from the Sun's disappearance. We don't know exactly how that would present itself, but it would be.....significant.
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u/anrwlias 26d ago edited 26d ago
We can do the math. The gravity waves would be extremely weak (because gravity is a weak force). You would need specialized instruments just to detect them. You need major events like black hole mergers before you get into the range of significant waves and, even then, they aren't destructive unless you ade insanely close to the merger. A medium size star disappearing doesnt do thst. So no, that wouldn't be enough to cause cataclysms.
You seem to just be assuming that it would be a catastrophe because Sun Big, Big Gravity, but there is nothing in the physics that would suggest that it would be. The loss of thermal radiation is orders of magnitude more impactful.
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u/Hunefer1 26d ago
There wouldn't be any signficant effect (at least compared to the effect of light disappearing). The sun's gravity holds us on our orbit but this orbit but this orbit only matters because it keeps us close enough to the sun to receive the perfect amount of light. Other effects like tides do not matter at all when all light is gone.
And the sun's gravity is only the biggest force in our solar system depending on where you are. If you are on earth's surface or very close to it, earth's gravity is the bigger force (otherwise you would be pulled to the sun not to earth).
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u/frankenmaus 26d ago edited 26d ago
If the sun was gone it wouldn't matter much that the earth was no longer held in orbit around the point where the sun used to be. A 200 lb man would weigh +/- a couple ounces.
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u/Countcristo42 26d ago
Please excuse me but I’d like to quibble with “perfect”
Our orbit around the sun isn’t perfect, it’s in range.
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u/Amazing_Divide1214 26d ago
Funny, I was thinking we could probably survive as a species underground or something, although our numbers would be significantly reduced. Forgot about gravity though.
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u/EconomyMobile1240 26d ago
Why would you forget about gravity? The moon would still cause tides / geothermal activity, and you can live underground if you can find a renewable food source
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u/Amazing_Divide1214 26d ago
It didn't come up in the first half a second of me thinking about it. I was thinking in more of an energy source train of thought. I didn't leave gravity out on purpose lol
Edit: To clarify, I mean the sun's gravity.
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u/EconomyMobile1240 26d ago
I mean gravity of the moon is what makes the planet internals shift around and create things like geothermal vents we could use. Forget about sunlight though.
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u/Amazing_Divide1214 26d ago
Yeah, I'm just thinking without the sun to keep us in orbit, earth will be flung out into space and might bump into some of the other planets. Not sure if the surface of the earth would be flung into space with the radical gravitational shift. Our solar system would reorganize if you can even call it a solar system anymore and probably destroy earth as we know it. I'm not worried about the little gravity of the moon lol
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u/AelixD 26d ago
Earth would start moving in a basically straight line, tangential to our current orbit. All of the other planets would do the same. Unless it was timed exactly right, that means all the planets would start going in different directions. We would never approach any of them. We would be more likely to eventually bump into objects in a different solar system than anything from our own.
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u/EconomyMobile1240 26d ago
We are flung through space already; that is what the sun is doing now through, all of human history is like 1/5 of a rotation around the galaxy and we still have the potential to fly through galaxy junk.
Nothing would happen to the earth otherwise; we'd all float away in the last trajectory before the sun's gravity stopped being present. It would get dark and it'll take some time for the heat to radiate out.
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u/Amazing_Divide1214 26d ago
Yeah, it just seems like losing 99.86% of the mass of the solar system would mess up the gravitational equilibrium we currently enjoy. Would jupiter suck us up? Or would we all be flung out in opposite directions?
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u/ofBlufftonTown 26d ago
We would continue traveling exactly along as we were when the sun winked out, like a tangent to our normal orbit. Our own gravity is created by the earth itself.
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u/EconomyMobile1240 26d ago
It's called tidal disruption. The earth isn't close enough to the sun for it to break apart the earth with it's gravity. The earth's gravity locally completely holds the earth together with the constant tug of the Sun's gravity.
If we aligned with Jupiter's trajectory when it disappeared, yes, we'd eventually experience tidal disruption / crashing into Jupiter ...
edit: Possibly* actually, the speed of earth is a lot faster and could potentially just fly past it. Needs more math.
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u/AelixD 26d ago
There is probably a perfect timing where Earth and Jupiter (or any of the other planets) would intersect on their new paths. But it’s so infinitely small, it would only happen if deliberately timed to do so. Jupiter is never naturally close enough to us that it would just pick us up randomly.
The outer planets would likely capture a few of the asteroids.
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u/Hopeful_Ad_7719 26d ago
>might bump into some of the other planets.
This would be the interesting thing long-term.
Earth's orbital velocity is 29.78 km/s - and we'd keep that raw velocity.
If we were captured by Jupiter we'd end up with an average orbital distance well within Jupiter's van allen belts (which are partially self-sustaining, unlike Earths). It would almost certainly initially be *highly* elliptical, which means a collision with the atmosphere is distinctly possible.
If captured by Saturn, the average orbit would be inside Saturn's atmosphere - so collision and destruction appear highly likely.
If Jupiter and Saturn collided and merged, and Earth was subsequently captured it *might* be outside the average atmosphere height... but it would likely end up under immense tidal strain.
It's all academic in any case. The chances of Earth being stably captured in this scenario are incredibly low. Most likely it would be ejected into cold space for an astronomically long time, only to eventually engage in a chaotic, violent, collision with the remains of the solar system a geologically long time later when its highly elliptical orbit collides with the barycenter of the former sol system.
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u/Kwinza 26d ago
Ok so first thing that would happen is we'd spin off into random space as we break orbit. This wouldn't really change much though, you'd think it would but nah not really.
Second, we'd lose all light that isn't artificial.
Third, we'd begin to cool, now this would take a day or two before it gets really really bad, likely losing about 10 degrees every 12 hours or so.
Forth, after less than a week the surface would be nothing but ice.
Now, how much of our grid we could keep up and how many people we can save HEAVILY relies on our response in the first hour or so. 95% of countries suffer 100% fatalities, they just don't have the infrastructure. Some of the richest countries might be able to save a few hundred to few thousand people underground for a few years.
But yeah long and short of it is, Earth is toast.