Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chris on 16/03/2013 22:36:45
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I was asked this interesting question on the radio the other day:
"Is a magnetic field a pre-requisite for hanging onto an atmosphere?"
In the case of Earth, we regard the answer as yes. We also use the loss of a magnetic field on Mars as the reason for the planet's subsequent drying and (we believe) lifelessness. The reason being that the presence of a magnetic field deflects the solar wind around the planet, reducing its ability to interact with, and carry off, the atmosphere.
Having said this, another listener then quite astutely asked "what about Venus?" which has a very dense atmosphere but only a tiny residual magnetic field, its own field having decayed long ago, presumably also following a similar cessation of its geodynamo.
I deferred to higher authorities at this point and said I would do some homework.
Can anyone help me?
Chris
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Try this Chris
Principles of Planetary Climate. (http://books.google.se/books?id=bO_U8f5pVR8C&pg=PA576&lpg=PA576&dq=do+planets+need+EM+field+to+keep+a+atmosphere+venus&source=bl&ots=olRnKiOZ48&sig=mJg4gOaDfbrHaYlTJ59nXBWJu0Q&hl=en&sa=X&ei=PfVEUZP6Oar44QTl84BA&ved=0CEIQ6AEwCA)
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Thank you; so they are arguing that accumulation of ionised species in the outer atmosphere has a shielding effect. But, they do say that this applies to heavier atmospheric species. So, presumably, if you don't have a magnetic field then you can't have an atmosphere much like Earth's?
Chris
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There is this too.
"Venus has a mantle which is much thicker and hotter than ours. This makes the planet extremely volcanically active, spewing great clouds of carbon dioxide and other greenhouse gases into the air. Additionally, it is believed that the heat of the mantle builds up until (about once every 700,000 years or so) it bursts through the crust of the planet all at once - which would not only produce a glut of greenhouse gases, but would boil off any water vapor into the upper atmosphere, where it would eventually be lost into space.
As a result, Venus is the victim of the greenhouse effect gone wild. At an average of 92 times Earth's atmospheric pressure at the surface, and temperatures exceeding 860 °F (460 °C), it is far too hot and dense for water vapor (or oxygen) to remain anywhere near the Venusian surface, and possibly reverse the effects."
And the mass of course, that must create a pressure due to gravity as you say. So where can one expect a planet to create a atmosphere without having a EM field? I don't know :) seem to be a lot of factors to it.
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And better add that this is a educated guess, about the mantle I mean. Don't expect anyone to get down there to drill a hole and see.
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Hmm, I'll stay here I think.
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This one seem like a compressed presentation of the reasons why there normally is expected to be a magnetic field? Magnetic Fields. (http://www.astronomynotes.com/solarsys/s7.htm)
(Also I have some weak memory of the solar winds actually, at times, can connect us to the sun, via some plasma? I'm not sure there, been some years ago since I read that one. And it doesn't matter for this one I guess? :) And this one I found interesting too partially transmitted signals form the Venus orbiter transmitter. (http://www-ssc.igpp.ucla.edu/personnel/russell/papers/partTrans_orbiter.pdf)
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Ahh, this should be the final nail in the coffin :) Venus behaves like comet during reduced solar wind pressure. (http://www.sott.net/article/257308-Venus-behaves-like-comet-during-reduced-solar-wind-pressure)
Please ignore the comments under though :)
Or you will start a new controversy with established theories.
the electrical plasma universe indeed.