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Magnetic field on Venus



 
 
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  #1  
Old June 8th 11, 02:31 AM posted to sci.space.policy
Dbdblocker
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Default Magnetic field on Venus

No magnetic field, why hasn't the sun blown away it's atmosphere?
  #2  
Old June 8th 11, 03:50 AM posted to sci.space.policy
Alan Erskine[_3_]
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Default Magnetic field on Venus

On 8/06/2011 11:31 AM, Dbdblocker wrote:
No magnetic field, why hasn't the sun blown away it's atmosphere?


Why would it do that? A magnetic field prevents/reduces radiation from
getting onto the planet, not the solar wind. That just goes sailing
right through.

The gravity of Venus, as well as the density of the atmosphere and the
distance from the Sun are what hold the atmosphere in place.
  #3  
Old June 8th 11, 05:37 AM posted to sci.space.policy
Brad Guth[_3_]
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Default Magnetic field on Venus

On Jun 7, 6:31*pm, Dbdblocker wrote:
No magnetic field, why hasn't the sun blown away it's atmosphere?


It's doing the best that it can, perhaps losing at most a few tonnes/
sec. The mainstream status-quo would suggest the loss at only a few
kg/sec, so there's a rather big discrepancy.

However, the solar wind itself tends to generate a sort of bow
shockwave kind of an electron induced magnetosphere, so there is some
limited protection to that robust (99% of which isn't going anywhere
unless Venus gets slammed by mega halo CMEs). Meanwhile the
considerable outflux or disassociation of elements from within Venus
(including water, hydrogen, oxygen and helium) are being continually
replenished from thousands of geothermal vents and more than a few
volcanoes.

It's thermal imbalance has been estimated as near 21 w/m2, which means
there's still a lot of planet innards getting loose. The much higher
metallicity that includes thorium and uranium is another interesting
consideration that's kinda out of step with our moderate metallicity
and perhaps even more like our lunar metallicity.

Venus just doesn't seem to add up to being one of the original
planets, unless our Earth is the oddball. Just a weird thought, but
could Venus or Earth have been in orbit of some other star?

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  #4  
Old June 8th 11, 05:49 AM posted to sci.space.policy
Brad Guth[_3_]
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Default Magnetic field on Venus

On Jun 7, 7:50*pm, Alan Erskine wrote:
On 8/06/2011 11:31 AM, Dbdblocker wrote:

No magnetic field, why hasn't the sun blown away it's atmosphere?


Why would it do that? *A magnetic field prevents/reduces radiation from
getting onto the planet, not the solar wind. *That just goes sailing
right through.

The gravity of Venus, as well as the density of the atmosphere and the
distance from the Sun are what hold the atmosphere in place.


What's the maximum and/or typical particle density/cm3 within our
magnetosphere?
  #5  
Old June 8th 11, 06:05 AM posted to sci.space.policy
Brad Guth[_3_]
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Default Magnetic field on Venus

On Jun 7, 6:31*pm, Dbdblocker wrote:
No magnetic field, why hasn't the sun blown away it's atmosphere?


http://cat.inist.fr/?aModele=afficheN&cpsidt=2768629
Résumé / Abstract
The potential of ISEE 1 spacecraft has been used to derive the plasma
density in the magnetosphere and its environment. First, we show that
using the equilibrium of currents flowing in and out of a spacecraft,
we could numerically derive a relation between the spacecraft
potential and the density of the surrounding plasma. After verifying
that this relation was in good agreement with the measurement of the
density made by other instruments during selected periods of time, we
apply this relation to the spacecraft potential measured continuously
from 1977 to 1984 on ISEE 1. An image of the plasma density in the
magnetosphere and its environment is obtained as a result. All
principal magnetospheric regions are clearly identified: the solar
wind with a density around 5 cm-3, the magnetosheath with a density
around 50 cm-3, the magnetosphere with a density around 1 cm-3, the
plasma sheet with a density around 0.5 cm-3, and finally, the more
tenuous tail lobes with a density below 0.1 cm-3. The plasma density
was observed slightly higher on the dawnside than on the duskside of
the magnetosphere. In addition, the magnetosheath was closer to the
Earth on the dawnside than on the duskside. When the magnetic activity
increased (recorded by the AE index), the dayside magnetosphere was
compressed/eroded by about 1 to 2 RE, while the plasmasphere/inner
magnetosphere became quite irregular and expanded in the dawn-midnight
and in the dusk-noon sectors. In addition, during high magnetic
activity, the plasma sheet at YGSM = 0 was thicker and slightly denser
than at low-activity. On the other hand, the flanks of the plasma
sheet were thinner and slightly less dense during high-activity than
during low-activity.

-

No specific data on what the solar wind generates for Venus, but it
could be nearly similar to the 50 particles/cm3 density.

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  #6  
Old June 8th 11, 06:15 AM posted to sci.space.policy
Alan Erskine[_3_]
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Default Magnetic field on Venus

On 8/06/2011 2:49 PM, Brad Guth wrote:
On Jun 7, 7:50 pm, Alan wrote:
On 8/06/2011 11:31 AM, Dbdblocker wrote:

No magnetic field, why hasn't the sun blown away it's atmosphere?


Why would it do that? A magnetic field prevents/reduces radiation from
getting onto the planet, not the solar wind. That just goes sailing
right through.

The gravity of Venus, as well as the density of the atmosphere and the
distance from the Sun are what hold the atmosphere in place.


What's the maximum and/or typical particle density/cm3 within our
magnetosphere?


Why? This thread is about why Venus's atmosphere doesn't simply blow
off - I've explained that.
  #7  
Old June 8th 11, 03:25 PM posted to sci.space.policy
Brad Guth[_3_]
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Default Magnetic field on Venus

On Jun 7, 10:15*pm, Alan Erskine wrote:
On 8/06/2011 2:49 PM, Brad Guth wrote:

On Jun 7, 7:50 pm, Alan *wrote:
On 8/06/2011 11:31 AM, Dbdblocker wrote:


No magnetic field, why hasn't the sun blown away it's atmosphere?


Why would it do that? *A magnetic field prevents/reduces radiation from
getting onto the planet, not the solar wind. *That just goes sailing
right through.


The gravity of Venus, as well as the density of the atmosphere and the
distance from the Sun are what hold the atmosphere in place.


What's the maximum and/or typical particle density/cm3 within our
magnetosphere?


Why? *This thread is about why Venus's atmosphere doesn't simply blow
off - I've explained that.


You stated a personal subjective interpretation that it doesn't blow
off. Others do not agree with that, especially of the helium blow-off
that's likely worse than Earth because of the active venting and
higher metallicity of Venus creates more atmospheric helium, the 10%
less gravity that doesn't hold onto helium as well and the heat plus
65 kg/m3 buoyancy insures helium goes directly to the top (well above
the clouds and begins to disassociate well above the O2 layer) at
roughly 140+ km where solar wind has direct unimpeded access.

Venus helium at .0012% = 5.8e15 kg, and that's not an element staying
put.
  #8  
Old June 8th 11, 04:01 PM posted to sci.space.policy
John Park
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Default Magnetic field on Venus

Alan Erskine ) writes:
On 8/06/2011 11:31 AM, Dbdblocker wrote:
No magnetic field, why hasn't the sun blown away it's atmosphere?


Why would it do that? A magnetic field prevents/reduces radiation from
getting onto the planet, not the solar wind. That just goes sailing
right through.


Don't think so. The solar wind consists of charged particles (mainly
protons) as far as I know--it will be deflected by a magnetic field. On the
other hand, the solar wind carries orders of magnitude less momentum than
ordinary sunlight, so a magnetic field probably won't make much difference
to a planetary atmosphere.

--John Park


The gravity of Venus, as well as the density of the atmosphere and the
distance from the Sun are what hold the atmosphere in place.



  #9  
Old June 8th 11, 05:31 PM posted to sci.space.policy
Doug Freyburger
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Default Magnetic field on Venus

Alan Erskine wrote:
Dbdblocker wrote:

No magnetic field, why hasn't the sun blown away it's atmosphere?


Why would it do that? A magnetic field prevents/reduces radiation from
getting onto the planet, not the solar wind. That just goes sailing
right through.


A magnetic field also keeps low energy charged particles in. Solar
ultraviolet radiation ionizes atoms in the upper atmosphere. Lacking a
magnetic field those atoms near the limb stream away with the rest of
the solar wind. With a magnetic field those atoms loop back towards the
planet and get combined back into molecules. On Earth this is a part of
how we get our ozone shield.

How much would be lost is a function of how volatile the atmosphere is.
You will note that Venus is notably lacking in water and other hydrogen
bearing molecules in its atmosphere. Perhaps the lack of magnetic field
was a large part in why the water went away and why Earth has managed to
keep hers.

The gravity of Venus, as well as the density of the atmosphere and the
distance from the Sun are what hold the atmosphere in place.


Also volcano gases give a new supply. As long as the new supply exceeds
the old amount, atmospheric pressure will build. It looks like that
happened a lot on Venus before a stable pressure was reached.
  #10  
Old June 8th 11, 11:19 PM posted to sci.space.policy
Dbdblocker
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Default Magnetic field on Venus

On Wed, 08 Jun 2011 12:50:31 +1000, Alan Erskine wrote:

On 8/06/2011 11:31 AM, Dbdblocker wrote:
No magnetic field, why hasn't the sun blown away it's atmosphere?


Why would it do that? A magnetic field prevents/reduces radiation from
getting onto the planet, not the solar wind. That just goes sailing
right through.

The gravity of Venus, as well as the density of the atmosphere and the
distance from the Sun are what hold the atmosphere in place.


Well, that's the reason they give for Mars thin to non-existent
atmosphere. No mag field, no protection.
Venus is closer than mars to the sun.
 




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