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Why does Venus still have an atmosphere?

foophil

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foophil
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I'm curious on this. Venus is roughly the same size as Earth. Our planet has a strong magnetic field helping to shield us. Venus has a very weak magnetic field, one that is caused by the solar winds itself. Mars has no magnetic field and has lost nearly all its atmosphere. Mars is smaller than Earth and Venus of course.

If Mars had an atmosphere and lost it due to the solar winds, why hasn't Venus? I am obviously missing something obvious, but my reading of the various Wiki articles and my Google-Fu hasn't found an answer I'm terribly happy with. I'm probably sorely misunderstanding something.

Anyone care to point me in the right direction? I know that Venus has a LOT of CO2 in the atmosphere, probably formed early on during its development, which lends it some extra protection from the solar winds. Maybe that is why it's atmosphere survived and Mars' didn't? I'd think that by now being as close as it is to the Sun that it would have had a lot blasted away by the solar radiation though.

Help a curious guy out please. :)
 
Venus' gravitational field is stronger at it's surface than that on the surface of Mars?
 
Red Baron Farms said:
Volcanism
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Could you elaborate? Lots of extra CO2 via volcanism released over a longer period of time, whereas Mars cooled off faster and slowed/stopped its release long ago?

How much longer until Venus loses its atmosphere? Will the Sun swallow it whole long before then?

Does that also mean Mars still has a lot of CO2 trapped inside since it cooled faster?
 
foophil said:
Help a curious guy out please. :)
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Whole bunch of great questions and the answer might surprise you. There is a growing body of information that suggests the planet was completely resurfaced about 500 million years ago in a massive bout of volcanism.

The planet seems to have settled down some, but going back through historical records there appears to still be some volcanic activity going on, and there could still be 3 or so major volcanoes erupting regularly in modern times. So far some 1600 major volcanoes have been identified on Venus. So the future is not promising for potential colonists
 
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MG1962 said:
Whole bunch of great questions and the answer might surprise you. There is a growing body of information that suggests the planet was completely resurfaced about 500 million years ago in a massive bout of volcanism.

The planet seems to have settled down some, but going back through historical records there appears to still be some volcanic activity going on, and there could still be 3 or so major volcanoes erupting regularly in modern times. So far some 1600 major volcanoes have been identified on Venus. So the future is not promising for potential colonists
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Oh wow, I hadn't realized it was that recent. That would certainly help explain it then. Thanks!
 
foophil said:
My apologies. I quickly read your first reply as magnetic field. :)
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I suspected so :D No problem.
As far as the volcanism is concerned, that could most likely answer the question why Venus' atmosphere is so dense.
The 'atmosphere' apparently got some heavy replenishment that might help make it so dense, but it's the gravity which keeps the atmosphere bound to the planet.
 
Reading a little deeper on Mars and I see that it too was volcanically active up until about 500 million years ago. I guess the gravitational field difference of ~90% of Earth's (for Venus) and ~60% of Earth's (for Mars) is a really big deal then.

I had thought the solar wind was more powerful than it really is I guess. I pictured it essentially stripping off Earth's atmosphere pretty quickly (cosmically speaking) if we ever lost our magnetic protection.
 
foophil said:
Reading a little deeper on Mars and I see that it too was volcanically active up until about 500 million years ago. I guess the gravitational field difference of ~90% of Earth's (for Venus) and ~60% of Earth's (for Mars) is a really big deal then.

I had thought the solar wind was more powerful than it really is I guess. I pictured it essentially stripping off Earth's atmosphere pretty quickly (cosmically speaking) if we ever lost our magnetic protection.
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It is not really gravity that causes the problem. Your original thought that it is linked to the magnetic field is closer to current thinking on the subject. With Earth the magnetic field blocks a lot of high energy particles interacting with the upper atmosphere. On Mars this did not happen, so as the high energy particles impact the various molecules in the upper atmosphere they impart energy allowing the molecules to escape
 
foophil said:
Reading a little deeper on Mars and I see that it too was volcanically active up until about 500 million years ago. I guess the gravitational field difference of ~90% of Earth's (for Venus) and ~60% of Earth's (for Mars) is a really big deal then.

I had thought the solar wind was more powerful than it really is I guess. I pictured it essentially stripping off Earth's atmosphere pretty quickly (cosmically speaking) if we ever lost our magnetic protection.
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I wonder if the solar wind would be able to strip such a dense atmosphere from a planet, a lot of heavy work it seems to me :)
 
MG1962 said:
It is not really gravity that causes the problem. Your original thought that it is linked to the magnetic field is closer to current thinking on the subject. With Earth the magnetic field blocks a lot of high energy particles interacting with the upper atmosphere. On Mars this did not happen, so as the high energy particles impact the various molecules in the upper atmosphere they impart energy allowing the molecules to escape
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Okay then. Mars had a magnetic field at one point and was thought to have lost it a few billion years ago right? Venus is thought to never have had one other than the weak one generated by the atmosphere's interaction with the solar winds. Both Mars and Venus had recent volcanic activity it would seem. So is the primary difference simply the gravitational field or not? Sorry for the confusion! :o
 
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Gravitational field is certainly a big difference between Mars and Venus. Also the atmosphere of Venus consists mostly of dense molecules.
 
RecoveringYuppy said:
Gravitational field is certainly a big difference between Mars and Venus. Also the atmosphere of Venus consists mostly of dense molecules.
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Did Mars not have dense molecules being put in the atmosphere by its volcanism? If it did, were they blasted away due to the smaller gravitational field? If so, I guess the differences really do mainly boil down simply to the mass of the planets.

Thanks everyone for keeping the 'E' in... um... ISF. (That doesn't work as well as when it was JREF).
 
foophil said:
Okay then. Mars had a magnetic field at one point and was thought to have lost it a few billion years ago right? Venus is thought to never have had one other than the weak one generated by the atmosphere's interaction with the solar winds. Both Mars and Venus had recent volcanic activity it would seem. So is the primary difference simply the gravitational field or not? Sorry for the confusion! :o
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I would suggest the scale of the volcanism is probably more to do with it. Mars basically only has volcanoes in one place, the Tharis bulge. Even then we are looking at about 5 major volcanoes.

I am sure on some level gravity does play a part, but to counteract that we are looking at stronger cosmic rays near Venus. So I think without events 500 million years ago, Venus would look much the same as Mars
 
foophil said:
Did Mars not have dense molecules being put in the atmosphere by its volcanism? If it did, were they blasted away due to the smaller gravitational field? If so, I guess the differences really do mainly boil down simply to the mass of the planets.

Thanks everyone for keeping the 'E' in... um... ISF. (That doesn't work as well as when it was JREF).
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Well the biggest, so we can assume the oldest and most active volcano on Mars actually projects outside the atmosphere, so everything spat out of Olympus Mons goes straight into space.
 
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