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Magnetic field and atmosphere


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#1    Razer

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Posted 10 December 2012 - 12:20 AM

I've read that the reason Mars has little to nothing of an atmosphere is because it has no magnetic field to shield it from the solar wind.  While  I don't disagree with that, what I don't understand is how Venus with basically no magnetic field either has such a dense atmoshpere. What's going on there? Two planets with no magnetic field to speak of and one with nearly no atmosphere and the other with an atmosphere that would crush you.


#2    Professor T

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Posted 10 December 2012 - 01:11 AM

I think that's because Mars has only about 1/9th earth gravity, and venus 91% Earth gravity.


#3    Waspie_Dwarf

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Posted 10 December 2012 - 01:19 AM

View PostProfessor T, on 10 December 2012 - 01:11 AM, said:

I think that's because Mars has only about 1/9th earth gravity
Actually Mars has about 1/3 of Earth's gravity at the surface (38% to be more precise).

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#4    Professor T

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Posted 10 December 2012 - 01:59 AM

View PostWaspie_Dwarf, on 10 December 2012 - 01:19 AM, said:

Actually Mars has about 1/3 of Earth's gravity at the surface (38% to be more precise).

damn, your right...
Trust me to check my facts and then get it wrong..


So, that theory doesn't cut the mustard.......

Theory #2..
Atmospheric replenishment..
With all the volcanic activity on Venus the Atmosphere is in a constant state of replenishment, whereas Mars has (as far as we can tell) no replenishment, except maybe rover fumes.. which is next to negligible.

Edited by Professor T, 10 December 2012 - 02:11 AM.


#5    A rather obscure Bassoon

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Posted 10 December 2012 - 04:18 AM

View PostProfessor T, on 10 December 2012 - 01:59 AM, said:

damn, your right...
Trust me to check my facts and then get it wrong..


So, that theory doesn't cut the mustard.......

Theory #2..
Atmospheric replenishment..
With all the volcanic activity on Venus the Atmosphere is in a constant state of replenishment, whereas Mars has (as far as we can tell) no replenishment, except maybe rover fumes.. which is next to negligible.
Venus is indeed the victim of the runaway Greenhouse effect ,being closer to the sun and an atmosphere that is 95% C02.Originally it may have had water but being closer to the sun it never liquified and remained in the atmosphere starting the Green house process.I'm sure that if i am incorrect then someone will correct me.

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#6    Razer

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Posted 10 December 2012 - 09:07 PM

View PostProfessor T, on 10 December 2012 - 01:59 AM, said:

damn, your right...
Trust me to check my facts and then get it wrong..


So, that theory doesn't cut the mustard.......

Theory #2..
Atmospheric replenishment..
With all the volcanic activity on Venus the Atmosphere is in a constant state of replenishment, whereas Mars has (as far as we can tell) no replenishment, except maybe rover fumes.. which is next to negligible.

Good point, also I didn't consider the difference in gravity.  Cheers.


#7    Professor Buzzkill

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Posted 10 December 2012 - 09:19 PM

View Postshaddow134, on 10 December 2012 - 04:18 AM, said:

Venus is indeed the victim of the runaway Greenhouse effect ,being closer to the sun and an atmosphere that is 95% C02.Originally it may have had water but being closer to the sun it never liquified and remained in the atmosphere starting the Green house process.I'm sure that if i am incorrect then someone will correct me.

Saying that venus is hot because of a runaway greenhouse effect (i.e. as a warning for earth) is incorrect. Venus' day is longer than its year meaning the sun has enough time to evaporate all liquids on the planet. Another factor is that Venus doesnt have plate movements like on earth. On Venus, large sections of the crust break open and slide into the mantle causing huge amounts of poisonous gases to vent into the atmosphere.

If either of these factors occured on earth then we would be in serious trouble.


#8    A rather obscure Bassoon

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Posted 10 December 2012 - 09:22 PM

View PostProfessor Buzzkill, on 10 December 2012 - 09:19 PM, said:

Saying that venus is hot because of a runaway greenhouse effect (i.e. as a warning for earth) is incorrect. Venus' day is longer than its year meaning the sun has enough time to evaporate all liquids on the planet. Another factor is that Venus doesnt have plate movements like on earth. On Venus, large sections of the crust break open and slide into the mantle causing huge amounts of poisonous gases to vent into the atmosphere.

If either of these factors occured on earth then we would be in serious trouble.

I think we may be ok for a couple of billion years or so,but i believe as the Sun gets older and hotter and lighter as it's Hydrogen fuel gets used up,then Earth will go the same way as venus.

Of course we all know the end result,the Sun goes Red Giant and swells eventually consuming all the inner planets.

Edited by shaddow134, 10 December 2012 - 09:30 PM.

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#9    sepulchrave

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Posted 11 December 2012 - 05:28 AM

View PostProfessor Buzzkill, on 10 December 2012 - 09:19 PM, said:

Saying that venus is hot because of a runaway greenhouse effect (i.e. as a warning for earth) is incorrect. Venus' day is longer than its year meaning the sun has enough time to evaporate all liquids on the planet. Another factor is that Venus doesnt have plate movements like on earth. On Venus, large sections of the crust break open and slide into the mantle causing huge amounts of poisonous gases to vent into the atmosphere.

If either of these factors occured on earth then we would be in serious trouble.
I agree that the length of the solar day has an impact on the temperature of Venus, but I think the greenhouse effect has a significant role as well. (Your second point simply provides the mechanism for the abundance of greenhouse gases in the atmosphere.)

The big point in favour of a dramatic greenhouse effect is the difference in surface temperature between Venus and Mercury, in my opinion. Mercury also has no plate movements, a solar day that is actually longer than Venus', and a maximum surface temperature of 700 K.

On the other hand, Venus is further from the Sun than Mercury but has an average atmospheric temperature of about 737 K.

Apart from a ``runaway greenhouse effect'' I don't see why Venus should be hotter than Mercury.

------

As to the OP, there is a wiki on the subject of the Martian atmosphere, lack of a magnetic field is only one of the possible reasons for not having a significant atmosphere.

Perhaps chemistry and geological activity might play a significant role as well; the atmospheres of both Mars and Venus are primarily carbon dioxide, but the surface of Mars is also red from iron oxide powder. Iron oxidizes more readily than carbon; without volcanic activity to separate the iron and the oxygen there may not have been enough oxygen on Mars to form carbon dioxide. Perhaps there are significant carbon deposits in the crust of Mars. (This is just idle speculation on my part.)





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