Why does Venus still have an atmosphere?

jaydeehess said:
On another scale,,,,,,Took a lot of heavy lifting to create the great pyramids. Given a lot of time though....:D
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Yeah I am not sure Solar Wind was responsible for that - But I have been known to be wrong before :boxedin:
 
As far as I am aware, even the Earth's gravitation can't hold atoms by their mass alone right up to Oxygen - luckily for us and anything that breathes - most atoms are bound into molecules and free ones have electric charges making them "sticky."

It takes a very long time indeed for oxygen or lighter to bump its way to the upper atmosphere and float off. I'd reckon that as Venus's atmosphere is highly active there are many forces in play keeping it where it is!

The sun is similar in that a nuclear particule in the interior active zone doesn't have far to go before it bumps into another - this action of course maintains the chain - but as the angle of "bump" is very precise in nuclear reactions even after several million bumps, said particule has not gone very far - in fact it may take upwards of 500,000 years for one to reach the surface. Once there and relatively free - it can get here in 8 minutes.
 
foophil said:
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?
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EDIT: missed the point sorry.
 
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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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So, what is the thinking here? That Venus' atmosphere was once completely stripped away by solar wind over the 1st 4 billion years (due to its proximity to the sun and its lack of a strong magnetic feld), then 500 million years ago, the surface was completely glassed by a massive era or volcanism, and a new atmosphere of CO2 created? If so, that is simply astonishing!
 
smartcooky said:
So, what is the thinking here? That Venus' atmosphere was once completely stripped away by solar wind over the 1st 4 billion years (due to its proximity to the sun and its lack of a strong magnetic feld), then 500 million years ago, the surface was completely glassed by a massive era or volcanism, and a new atmosphere of CO2 created? If so, that is simply astonishing!
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Well it is definitely a work in progress. And there are a few competing theories about what things were like before all hell broke loose. I guess the joker in the pack is when did Venus lose its magnetic field?
 
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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Well for one thing the surface gravity of Mars is about 38% that of Earth so that a 100 kg person would weigh 38 kg on Mars. Venus in contrast the same person would weigh 91 kg. The surface gravity of Venus is about 2.4 that of the surface gravity of Mars. Further the escape velocity of Earth is 11.19 km/s, that of Venus is 10.36 km/s, and that of Mars is 5.03 km/s. Venus' escape velocity is 92% that of Earth's whereas Mars' is only 45% that of Earth's. Venus's escape velocity is more twice that of Mars.

Also it is my understanding the amount of energy required to get something to escape velocity does not go up arithmetically. So that double the escape velocity does not mean that you just double the energy required to get to escape velocity. It requires a greater than doubling the energy to accelerate to that velocity.

The above probably explains a lot about why Venus retains its dense atmosphere and Mars did not. retain most of its.
 
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Pacal said:
Well for one thing the surface gravity of Mars is about 38% that of Earth so that a 100 kg person would weigh 38 kg on Mars. Venus in contrast the same person would weigh 91 kg. The surface gravity of Venus is about 2.4 that of the surface gravity of Mars. That probably explains a lot about why Venus retains its dense atmosphere and Mars did not. retain most of its.
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If the atmosphere was retained purely due to gravity and distance from the sun then both would have a similar atmosphere. Mars is twice the distance from the sun as Venus is. So Mars would have only a quarter of the rays from the sun.
 
The Venusian atmosphere is the result of a runaway greenhouse effect, coupled with an absurdly slow rotational period. The planet is large enough to hold onto heavier molecules that don't get blown away by the solar wind. Combined with rampant volcanic activity, the atmosphere is pumped full of acidic compounds and gases that stick around. The entire surface is regularly "repaved" during periods of high volcanic activity. It's estimated that this occurs every 500,000,000 years or so, based on the evidence that the current surface is relatively free of impact craters. I often wonder what Venus would look like if it had a normal rotational period.

The Martian atmosphere is thin due to the lack of a protective magnetic field. The Earth's magnetic field helps protect the atmosphere from the effects of solar wind. Because Mars lacks a field (or at least lacks a strong one), any lighter molecules get stripped away quickly, and the subsequent UV radiation makes it hostile for any organic processes. If Mars had a larger iron core, it's possible that it could have remained viable for longer. As it is now, I believe the current accepted model is that Mars is geologically dead, or close to it.
 
MG1962 said:
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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Only if it's projected out at or above escape velocity, surely?
 
Vermonter said:
The Venusian atmosphere is the result of a runaway greenhouse effect, coupled with an absurdly slow rotational period.
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My opinion:

What is called greenhouse effect in the case of Venus is nothing more than atmospheric heat insulation over hundreds of millions of years. Gases are excellent insulators. (See)​

Cheers, Wolfgang
 
Damien Evans said:
Only if it's projected out at or above escape velocity, surely?
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A proportion of gas molecules would be at escape velocity. Especially for lighter molecules.


http://en.wikipedia.org/wiki/Maxwell–Boltzmann_statistics


An examle showing the general gist:
300px-Maxwell-Boltzmann_distribution_1.png


Maxwell–Boltzmann statistics can be used to derive the Maxwell–Boltzmann distribution of particle speeds in an ideal gas. Shown: distribution of particle speed for 106 oxygen particles at
−100, 20 and 600 degrees Celsius.
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jimbob said:
A proportion of gas molecules would be at escape velocity. Especially for lighter molecules.


http://en.wikipedia.org/wiki/Maxwell–Boltzmann_statistics


An examle showing the general gist:
[qimg]http://upload.wikimedia.org/wikipedia/commons/thumb/3/36/Maxwell-Boltzmann_distribution_1.png/300px-Maxwell-Boltzmann_distribution_1.png[/qimg]
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Does that imply they continue for some distance with the same velocity, or do they merely go a short way, collide with another molecule, and reset everything? In other words, does that graph mean they really get off the planet, or that they sometimes move really fast?
 
From what I remember, gas molecules have elastic collisions which would mean that the kinetic energy is conserved i.e. they don't slow down. With a lower pressure, the distance between collisions would be further.
 
wogoga said:
My opinion:

What is called greenhouse effect in the case of Venus is nothing more than atmospheric heat insulation over hundreds of millions of years. Gases are excellent insulators. (See)​

Cheers, Wolfgang
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And that is not a greenhouse effect why?
 
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