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team-tree-syndicate t1_j27zrp4 wrote

Reply to comment by [deleted] in How much does the liquid magma of the Earth affect it's surface temperature? by tripperfunster

I got a question, I'm assuming that by an active core making an atmosphere possible, you mean by the magnetic field, correct? If so, I wonder how a magnetic field helps keep an atmosphere in place. I thought that gravity was the contributing factor for that?

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dwkeith t1_j280owa wrote

Deflects solar winds which would otherwise strip the atmosphere.

Wikipedia has a good overview of how it works https://en.wikipedia.org/wiki/Magnetosphere

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CrustalTrudger t1_j28zd88 wrote

This is not correct though. Good counterpoints are Venus, which has no intrinsic magnetic field, only a relatively weak induced one, and yet still has a thick atmosphere or Mercury, which has an intrinsic magnetic field and effectively no atmosphere. This comes up a lot on AskScience and there are numerous threads considering the relative role of gravity, active volcanism, and magnetospheres for keeping planetary atmospheres, e.g., this thread where various posters lay out the details and highlight that gravity / escape velocity is the dominant factor in whether a planetary atmosphere is maintained, this specific comment by one of our panelists addresses this misconception directly.

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pmalleable t1_j2b4g17 wrote

So is the relatively small atmosphere on Mars entirely or mostly due to the lower mass of the planet?

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Gohanthebarbarian t1_j2bbu3v wrote

Yeah it makes intuitive sense that the higher mass rock balls would be more likely to hold onto their atmospheres.

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CrustalTrudger t1_j28zuu0 wrote

You are correct, gravity / escape velocity is the primary control and the replies indicating that the presence or absence of a magnetosphere are the primary control reflect a common misconception (e.g., see this post).

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Eternal-brah t1_j280oh6 wrote

That's actually an interesting question, About how magnetic fields really traps "anything". Tonight I will be going down a rabbit hole.

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team-tree-syndicate t1_j280sst wrote

After some thinking, my best guess would be the prevention of radiation from the sun. Without a magnetosphere, cosmic wind would "blow" away the atmosphere.

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cismo2010 t1_j28bgwe wrote

Just to bei more specific, the radiation from the sun which get's blocked/deflected by earths magnetic field are charged particles (e.g. alpha/beta-radiation).

The radiation which "heats" earth ist gamma-radiation in form of photons. A good portion of those photons get reflected by clouds and ice (due to the reflectiveness of white surfaces), another part afterwards get's radiated as infrared-radiation. The Difference between the incoming and (reflected + radiated) photons are the energy earth get's from the sun.

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