# Q: What would Earth be like if it didn’t turn?

Physicist: The side of the Earth facing the sun would quickly become hotter than boiling water, and the side facing away would be cold enough for the atmosphere to freeze solid (condense into nitrogen and oxygen ice).  So all of the air and water would form glaciers of ice and what-was-once-air on the night side of the planet, and the day side of the planet would become an airless desert.  Without air to scatter sunlight, the sky would always be black, and the stars always visible.

Here I’m assuming that the Earth, rather than not rotating at all (which would result in one-year-long days), is in “phase lock” with the Sun the same way the Moon is in phase lock with the Earth.  So one side would always face the Sun and the other would always face away.

Air and water on the dark side of the earth would freeze. The Earth would be half desert, half water/air glaciers, and all atmosphere free.

We can estimate how hot and cold things would get by considering the Moon.  It’s the same distance from the Sun as the Earth is, so it’s a good test case.  Very quickly (within a few minutes) after the Sun rises at the beginning of the Moon’s 709 hour day the surface gets about as hot as it’s going to get: a balmy 110°C/230°F (give or take).

Some craters on the moon are never exposed to sunlight at all, which is exactly the situation the dark side of the Earth would be in, writ small.  They get as cold as -240°C/-400°F (that 30°C above absolute zero!).  That’s cold enough to freeze oxygen and nitrogen solid, even without air pressure.  So on the day side everything would get roasted, the oceans would evaporate out of their basins, and then drift to the dark side where they would form and condense onto massive glaciers.

For water at least, this is an effect already at work on our Earth (“spin Earth”?, “Rotopolis”?), it just doesn’t get very far.  That’s why (for example) the Antarctic ice cap is on average about as thick as the ocean is deep!

The non-rotating planet is a staple of sci-fi, and generally it’s declared that life could survive in the “twilight ring” between the day and night sides.  In fact, in the twilight ring the temperature would be colder than our poles are today (which are kinda like “twilight points”).  You find the “comfortable zone” about 20° into the day side from the ring.

Not that it matters.  What with the atmosphere being in such a state that you’d need a hammer and chisel to breathe, it wouldn’t be possible for life to exist anywhere.  The set up we have now is pretty good by comparison!

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### 15 Responses to Q: What would Earth be like if it didn’t turn?

1. So, a related question: suppose Earth was in the above state: phase lock with the Sun, no life at all, a desert hemisphere and another full of frozen air. Then an advanced alien species finds it and decides it’s a perfect candidate for terraforming, what with all the available water and such, with the added benefit that it’d “just” require making it spin once every 24 hours or so for things to settle into a nice pattern after a while.

What would be energy requirements of something like this? How could it be done (I’m guessing that gluing rockets to the ground and to the top of mountains wouldn’t work)? How much time would it take? And once the Earth was spinning, how long would our hypothetical aliens have to wait to be able to start colonizing it (think the frozen air and ice melting into an atmosphere and ocean, plus a climate regime, similar to ours)?

I’d love to have these questions analyzed in a future article.

2. The Physicist says:

The Earth has about $2.5\times 10^{29}$ Joules of energy tied up in its rotation right now (about $6\times 10^{19}$ tons of TNT), which is just stupid-alot. It’s hard to say how long it would take. Suppose it depends on how motivated the aliens are?
I couldn’t even give a ball park guess for how long it would take for all the ice that’s supposed to melt, to melt. I once made a really big snowman that didn’t melt completely until July. So… tens of thousands of years? We really need to get some kind of resident climatologist.

3. Jean-Paul says:

Because the earth is not spherical, wouldn’t air and water rush to the poles to achieve a more spherical shape? (Before it freezes, of course)

4. The Physicist says:

The Earth itself would probably settle into a more spherical shape on its own. But you’re probably right, the poles would get slightly thicker caps.

5. sergey melnik says:

why would you “need a hammer and chisel to breathe”?
how would no rotation affect the atmosphere?

6. sergey melnik says:

Oh! i see! the joke is that the atmosphere would freeze up and be stranded on the other side. so you would need a hammer and chisel to extract it. HA HA!! (am i right?)

7. The Physicist says:

Yes!
Definitely the best joke yet.

8. Alistair says:

I was just wondering what would happen if the moon were to suddenly just disappear what would happen to the earth?

9. shioru says:

Can the 2.5 x 10^29th power Joules of energy be generated with something like the theoretical moon forming event? You know, a huge asteroid slamming into the earth?

Which also brings up my next batch of questions:
i) Does the moon’s existence or non-existence affect the resultant rotation? Would having a moon help with starting the rotation, or as the current situation, slowly slowing the earth’s rotation?
ii) What are the chances of the planet-slamming event creating a moon/second moon? Other possible outcomes? (like a ring around the earth, for example)

10. The Physicist says:

The thing that hit the Earth and formed the moon (according to the most recent simulations) was about the size of Mars (it’s been posthumously named “Theia“), and that should be enough to get the Earth spinning again. However, it would also liquify the surface. But, if that’s not a problem, then slamming the Earth with something gargantuan should do the trick.
The moon’s orbit is related to the rotation of the Earth. Since the moon’s formation it’s been slowly leaching away angular momentum from the Earth, making our days longer and the moon’s orbit higher (it started out about 15 times closer).
If the Earth were not spinning, the moon would very, very slowly start Earth’s rotation back up again, until the Earth and moon were both in phase lock (same sides always facing each other).
I don’t know what fraction of the simulations end with a new moon being created, however I’d wildly guess that the presence of our present moon might actually screw up the formation of a new moon. Small ring system; for a while, probably.

11. Alexander Cooke says:

Wouldn’t the atmosphere transfer heat from one side to the other. Cooling the sun side and warming the night side up enough for there to be an atmosphere.

12. The Physicist says:

Maybe!
But it shouldn’t take too many areas on the dark side where the air is liquifying for the atmosphere to disappear.

13. Alexander says:

The atmosphere would stop this from happening.
Example EARTH.
The poles have MONTHS of constant night at a time and this scenario doesn’t happen! The record cold is -89c/194k
If the planet was very watery, then the parts with constant strong sunlight would have large amounts of water evaporating, the water would then be replaced by water currents from colder places, this woauld keep the maximum temperature at something where evaporation is quite rapid, 70c-90c maybe? The evaporating water would travel to darker areas and then rain down, so there would be a lot of cloud cover. This would likely help spread the heat. Overall the bigger the atmosphere the better it would be.