# What would the atmosphere do if the Earth were to vanish

1. Jul 21, 2015

### bland

If the Earth were to vanish.

Like the thought experiment that posits the sun suddenly disappearing to explain the 8 minute delay in the effect on the Earth, so I posit the Earth from the surface down vanishing in equally metaphysical and mysterious circumstances in order to help me to see what the atmosphere would do.

So we'd suddenly have a spherical ball of gas with an Earth sized hold in the middle. I understand that the air at ground level has a fair bit of mass about 1.2kg per sq metre, so there's going to be a fair bit of mass in the atmosphere.

What would happen and how long might it take. Would it collapse into a solid ball of air, or burst into flame, due to the temperature and the oxygen the collapse, if there was one, would generate, or would it sort of hang there for a very long time doing nothing much at all?

Would there be a separation of the layers where the denser lower layer would fall inwards, while the outer lay would float away into space, or would all the layer collapse at the same time seeing as everything falls at the same rate.

I think it would collapse but what I'd like to find out, is how dense it would get. But I'm curious to know if it would support itself seeing as it would have a perfect spherical but hollow size like I guess a solid mass would due to there being no difference in pressure on the inside and outside.

2. Jul 21, 2015

### A.T.

Sounds like a perfect question for:
https://what-if.xkcd.com/

I guess initially the air shell would expand in both directions (get thicker) due to pressure. I don't know if there could be some equilibrium like for the gas giants, or if it would just dissolve in the long term. Maybe the Moon would steal some of it?

3. Jul 21, 2015

### willem2

All the air would certainly spread out rather quicky.

The mass of the atmosphere is only 5.148*10^18 kg. This is less than a millionth of the mass of the earth (5.972 * 10^24 kg).
The energy needed for an air molecule to escape will be less than a millionth of what it is now and the escape velocity will be around 10 m/s (at 1 earth radius)
The atmosphere is also rotating, with a speed of 450 m/s at the equator and a speed bigger than 10 m/s almost everywhere except very close to the poles.

If the earth wasn't rotating, maybe a substantial part could end up at the center, but it would still dissipate rather quickly, unless you could keep it very cold.

4. Jul 21, 2015

### gsal

And, yes, without the gravitational force of the earth, the atmosphere will not have to be so compressed and it would tend to expand possibly in both directions (radially in and radially out), but I don't know, I am rather thinking it just "expand" radially out to the point of flying away the way a boleadora flies away when you let go of (or cut) the string (earth gravity).

I don't think the moon will stick around to steal atmosphere gases...it will also be long gone (boleadora, too)

I don't know much about this, but with the earth gone, so will be the magnetic field that protects us from so many solar things like certain particles and other winds...I wonder if those will simply blow the atmosphere away, whether together or dispersing it.

5. Jul 21, 2015

### A.T.

The Moon will go into an orbit around the Sun, and so will the spreading gas cloud. How close they get after which time depends on the timing of the Earth's disappearance.

6. Jul 21, 2015

### rootone

You would presumably have a vacuum where the Earth used to be.
Immediately outside of the vacuum would be the highest density of air, (previously the ground level air), so one thing I expect would happen initially is that this inner layer of air would collapse filling the vacuum until things were more or less in equilibrium.
Outer layers of the atmosphere would spread outwards as gravity is longer stopping it, so fairly quickly all there is left would be a thin cloud of gas.
It is possible that some of the heavier gases could be retained by the moon for a while, but probably not for very long

7. Jul 22, 2015

### 256bits

It would be a free expansion so the temperature should remain the same, along with the average kinetic velocity of the molecules.
I don't see any way for the gas to become cool.

8. Jul 22, 2015

### jbriggs444

If the gas were still confined within a container of finite size then I would agree that temperature would remain constant. But we are talking about an assembly of gas molecules that, once the Earth is removed, are not confined at all. If you restrict your attention to any finite parcel of gas, that parcel will have a bulk motion in a particular direction. The temperature of such a parcel computed based on the random kinetic energy that remains after the bulk motion is subtracted out will be lower than the starting temperature of the Earth's ambient air.

9. Jul 24, 2015

### Gaz

Well this one seems pretty easy to me. Without Earth's Magnetic field to protect it it would be swept away by solar winds.