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Who cares about Earth's magnetic field and ozone layer?

by Jon Richfield
Tags: aurora
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billiards
#37
Aug18-10, 01:32 PM
P: 747
Quote Quote by Jon Richfield View Post
There was a reply from Billiards in my notifications, but I seem unable to find it on line. I trust that he will forgive me for working from the notification instead of the forum entry.

1. My apologies for calling you Bill. It was not intended to represent your name, but as an abbreviation for Billiards. I am sorry if the abbreviation gave offence. In future I shall spell it out to avoid unnecessary bile or bickering.
2. "The magnetosphere does in fact deflect high energy particles from equatorial regions."
This is a very interesting assertion and deserves some amplification. I hope you (or anyone else in forum) will be willing to expand on it, even if we only consider charged particles. Trivially, any charged particle not travelling parallel to the "lines of force" (an equally trivial concept that we might as well neglect in practice) will be deflected by a magnetic field in the sense that its path will be altered. However, it does not follow that it will be deflected in a mode and to a degree that will protect whatever lies below. For example, a TeV or PeV particle would hardly notice our magnetosphere, whereas the typical solar wind particle is hardly "high energy"; if it were deflected it would in due course wind up either in a van Allen belt or at a pole, or perhaps in the atmosphere, where it would rapidly thermalise. Now, suppose that some charged particle does escape the clutches of the magnetosphere, or that the magnetosphere vanishes; how far might we expect it to penetrate the atmosphere with any significant energy excess at all? It might be instructive to consider as an illustrative example, the altitude to which the aurorae descend before they peter out. So far Billiards, this does not seem to suggest much increase in hazard to equatorial inhabitants, beyond what the atmosphere can handle very comfortably. But the whole reason for this thread, please remember, was to find out what I had overlooked or misunderstood. Please contribute! Mugaliens wasn't much help; expects me to do all the worrying myself! <mttr mttr!>

Meanwhile, all the best!

Jon
Yes there was a reply from me but I deleted it. The reason it was deleted is because it did not add any value to the thread and I felt it was better to get rid of it before it became entangled. I was in merry spirits when I made that post, and it was a rather crude, egregious, satirical dig at you posting style, which I later regretted when I started to sobre up. Anyhow, it looks like you read it, and I apologise, but I am glad that it does not seem to have caused you offense.

I do prefer Billiards to Bill, but that was not the thing that caused offense.

Now that I read more of your posts I think I "get them" more. When I first read them they read like snide personal attacks delivered in an arrogant condescending way, but actually on second anlaysis I find them to be the ramblings of a curious, sharp mind with a slightly odd sense of humour, and little concern for charm (that's just my personal interpretation -- and it means nothing more, or less, than that -- no doubt I am completely wong!). As you can probably tell, I am not an obsequious person, and I have little concern for charm (unless you're my girlfriend's parents!) I am also lazier than the average poster here in that I refuse to trawl through the net to find evidence which will make/refute someone else's point -- unless it happens to overlap with my own personal interests and I happen to be in a good mood.

Anyway, enough of that, I am ready to move on..
billiards
#38
Aug18-10, 02:03 PM
P: 747
Jon,

I agree that the atmosphere will protect us from the solar wind, with or without a magnetic field.

There is the issue of atmospheric stripping, but my reading around has not shown this to be hugely significant.

Without a either a magnetic field or an atmosphere the solar wind would be damaging to us. Low energy electrons can damage DNA. http://iopscience.iop.org/1402-4896/...707D2EB86D8.c2

The magnetic field would protect us if there were no atmosphere (ignoring the absurtity of living on a planet without an atmosphere).

I said earlier that I am not obsequious -- but this has been interesting, and I am glad you gave me reason to do a little reading -- for that I am grateful. Next time a lecturer warns of the dangers of losing the magnetic field, I will make sure to raise a few questions, and hopefully learn a little more.

I will share thi website which I found to be quite informative: http://www.phy6.org/Education/index.html
Jon Richfield
#39
Aug18-10, 02:35 PM
P: 258
Quote Quote by Ophiolite View Post
you suggested somewhere above that the loss of the magnetosphere may not cause any problems. There is one that immediately springs to mind: atmospheric erosion by the solar wind. This is a very real phenomenon. It is probably the primary cause for the low atmospheric pressure on Mars. I suspect there would be other deleterious effects though I share with you the belief that the doomsayers are greatly exagerating these.

One point no one seems to have brought out is that during a pole switch there is no point at which the field disappears entirely, it simply weakens and becomes more complex.
Thanks Ophiolite.
I agree that the ablation of the atmosphere is (to my eye at least) the most substantial concern in the event of loss of the magnetosphere. I am however, still a little sceptical of that as well.
See, (in the light of recent castigation of my tendency to neglect citation at the refereed publication level, I am hesitant to make hard assertions) it seems to me that in the absence of a magnetosphere there should be solar wind particles of three kinds from this point of view: Those that miss us completely, those that hit us (our atmosphere anyway) directly, and those that skim the atmosphere and knock atmospheric particles into escape trajectories. So far, so mundane, right? So let us ignore the first class, as being essentially irrelevant.
Next, consider the particles that "hit us directly". These are particles of whatever energy, that do not strike the atmosphere tangentially. They will generally, whatever transient ionic states they may assume, end up as components of atmospheric molecules, whether hydrogen, water, ammonia or the like. All right, some metals also might arrive, eventually becoming part of the Earth's crust or the biosphere, but they would be in the vanishing minority. In general, refer to all these particles as accreting.
In short nearly all such particles would contribute either to the atmosphere or the hydrosphere.
Finally let us consider those that I might call tangential impactors. By this I mean that they are not quenched in the atmosphere, but remain in space and each takes at least one atmospheric particle with them.
For current purposes, I propose that any molecules of water be regarded as part of the atmosphere (unless you think of serious logical objections).
Now, obviously this reduces the problem to a comparison between the rates of ablation and accretion. That sounds very simple, but as you will recognise (probably well ahead of me) there is no way to tell from first principles which of the two is greater, and by how much. If I were to guess, I should expect accretion to reign, but I could not defend the idea with any confidence. What is more, I could not even argue very strongly for the net rate of ablation to be very low. The fact that Mars and Mercury are nearly without atmosphere hardly figures, because Venus, with its negligible magnetosphere, has a very nice atmosphere, thank you, and it is between the two in its orbit round the sun.
Frankly, I would hate to bet whether a billion years without magnetosphere would cause us to run much short of air, but I am perfectly aware that I am in no position to defend the position very strongly, only that the area of interception of accretion material exceeds the area of ablation, and the conditions for accretion of a particle are far less demanding than for ablation.

You are right of course, about the state of the magnetosphere during the switch, but I have no idea whether the effect will differ significantly from a negligible magnetosphere.

Comments welcome, as always!

Cheers,

Jon
Jon Richfield
#40
Aug18-10, 03:04 PM
P: 258
Quote Quote by billiards View Post
There is the issue of atmospheric stripping, but my reading around has not shown this to be hugely significant.
Thanks. This is consistent with my impressions, but as I said to Ophiolite, I am hugely uncertain.

Without a either a magnetic field or an atmosphere the solar wind would be damaging to us. Low energy electrons can damage DNA.
Fairly low, anyway! I must say I was slightly surprised by the 3 eV figure!
But my rejection of that risk was rather because I reckoned that the tissue penetration of free, thermalised electrons would be trivial.

The magnetic field would protect us if there were no atmosphere (ignoring the absurtity of living on a planet without an atmosphere).


I said earlier that I am not obsequious -- but this has been interesting, and I am glad you gave me reason to do a little reading -- for that I am grateful. Next time a lecturer warns of the dangers of losing the magnetic field, I will make sure to raise a few questions, and hopefully learn a little more.
Billiards, I can hardly say how much I appreciate your generosity and courtesy in reacting in this way to a difficult situation. No one knows better than I that it is far harder to mend a bad atmosphere than to establish a good one. I admire your positive attitude and envy the lecturer, should your anticipated warnings and questions materialise. I always have appreciated class members who have gone intelligently beyond the prescribed work. A word to the wise though: if the lecturer loses his cool, let it go! Hell hath many furies like unto the Politically Correct when their views are called, however reasonably and sweetly, in question. But even those furies are not kept in Hell for nothing!

I will share thi website which I found to be quite informative: http://www.phy6.org/Education/index.html
Thanks; looks like a nice site. I'll fossick around a bit.

All the best,

Jon
Ophiolite
#41
Aug19-10, 04:37 AM
P: 274
Jon,
you are trying to assess the impact of the solar wind on our atmosphere through logic. I prefer to look at the facts.

You mention that Venus has retained a thick atmosphere despite having no magnetic field. However consider this research. I have emboldened the central point.

Zhang,T.L. et al Little or no solar wind enters Venus' atmosphere at solar minimum, Nature, Volume 450, Issue 7170, pp. 654-656 (2007).
Abstract

Venus has no significant internal magnetic field, which allows the solar wind to interact directly with its atmosphere2,3. A field is induced in this interaction, which partially shields the atmosphere, but we have no knowledge of how effective that shield is at solar minimum. (Our current knowledge of the solar wind interaction with Venus is derived from measurements at solar maximum.) The bow shock is close to the planet, meaning that it is possible that some solar wind could be absorbed by the atmosphere and contribute to the evolution of the atmosphere. Here we report magnetic field measurements from the Venus Express spacecraft in the plasma environment surrounding Venus. The bow shock under low solar activity conditions seems to be in the position that would be expected from a complete deflection by a magnetized ionosphere. Therefore little solar wind enters the Venus ionosphere even at solar minimum.


The strength of this interaction (induced field) I understand to be due to the thickness of the Venusian atmosphere, so one would not expect the same reaction were the Earth to lose its field.
Jon Richfield
#42
Aug19-10, 06:53 AM
P: 258
Quote Quote by Ophiolite View Post
Jon,
you are trying to assess the impact of the solar wind on our atmosphere through logic. I prefer to look at the facts.

You mention that Venus has retained a thick atmosphere despite having no magnetic field. However consider this research. I have emboldened the central point.

Zhang,T.L. et al Little or no solar wind enters Venus' atmosphere at solar minimum, Nature, Volume 450, Issue 7170, pp. 654-656 (2007).
Abstract

Venus has no significant internal magnetic field, which allows the solar wind to interact directly with its atmosphere2,3. A field is induced in this interaction, which partially shields the atmosphere, but we have no knowledge of how effective that shield is at solar minimum. (Our current knowledge of the solar wind interaction with Venus is derived from measurements at solar maximum.) The bow shock is close to the planet, meaning that it is possible that some solar wind could be absorbed by the atmosphere and contribute to the evolution of the atmosphere. Here we report magnetic field measurements from the Venus Express spacecraft in the plasma environment surrounding Venus. The bow shock under low solar activity conditions seems to be in the position that would be expected from a complete deflection by a magnetized ionosphere. Therefore little solar wind enters the Venus ionosphere even at solar minimum.


The strength of this interaction (induced field) I understand to be due to the thickness of the Venusian atmosphere, so one would not expect the same reaction were the Earth to lose its field.
Thanks Ophiolite, there is some interesting material there. I did some following up and came away with deeper reservations than ever. Consider the following quote from:
www.lpi.usra.edu/meetings/lpsc2009/pdf/1408.pdf.
"The magnetic field of the solar wind can both act as a shield and as a facilitator for removal of the atmosphere. The magnetic field piles up on the forward side of Venus and creates an obstacle to the flow."
If nothing else, the hits I found supported your preference for empirical evidence, which was in various ways very ambiguous. (Let's leave the concept of "facts" to the metaphysicians shall we!)

I do take your point about the difference between the thickness of the atmospheres of Earth and Venus, but I think you would agree that the nature of its influence is not unambiguous, magnetic field or not.
Now, one of the sources I found estimated the rate of loss of Venusian atmosphere under the influence of the solar wind at roughly 1e25 ions/sec. That seems to me to approximate 1 kg/s or thereabouts, which amounts to about 1e4.5 tonnes/Y. Given the Earths atmosphere at about 1e15.5 tonnes, and that of Venus being about 100 times more, it seems that Venus could stand that rate of leakage for some 1e13 years. Whether to extrapolate that to Earth at 1e11Y, I do not know, but let's assume that we could afford to lose 10% of our atmosphere if our magnetosphere vanished. That would should take us something like 1e10Y, which is roughly twice the current age of the planet, and over two thirds the estimated time since the big bang.
Please check my figures for reasonability and accuracy, assuming that my sources are at least reasonably sound. I am of course assuming a spherical herd of spherical cows, but if you know where to find square cows in this particular pasture, do tell!
Of course, neither logic nor empirical data are adequate at this stage of play, so not a word I say is to be taken very seriously. In fact, it is by no means clear to me why at present we should be terribly sure whether the magnetosphere isn't increasing our net rate of leakage. In the case of Venus for example, it seems that most of the losses are via the magnetotail, with extremely low penetration of the bulk of the atmosphere at solar minimum. If there were no magnetic shielding as a result of the interaction with the solar wind, Venus might be gaining atmospheric material from the solar wind.
I do not urge that as a prospect of course, but it seems no less reasonable than some other proposals.
Be all that as it may, if the back of my envelope isn't in desperate need of a new battery, I think I'll shunt my concerns over the rate of atmospheric ablation in the event of total loss of magnetosphere, firmly to the back burner!
Thanks for that material. Very illuminating. Billiards dropped a hint that the losses might not be very impressive, and I feel better and better about having raised the question in general. I am grateful to all you chaps for your contributions (even Mugalien's failure to worry me!)
Now all we need is a totally new contribution to turn up a totally new aspect to the topic.
Any bets anyone?
Cheers,

Jon
billiards
#43
Oct31-10, 05:43 PM
P: 747
Atmospheric stripping by the solar wind on Venus preferentially strips helium, hydrogen, and oxygen.

This may be the critical observation in understanding why Venus is so dry today. Perhaps the solar wind has gradually stripped the planet of water.
http://www.esa.int/esaMI/Venus_Expre...G373R8F_0.html

(The findings appear in the 29 November issue of the scientific journal Nature, in the paper: 'Venus loses its water through the plasma wake', by S.Barabash et al..)

The point is, perhaps the magnetosphere is important to us (and all life) here on Earth, as it has stopped our planet from drying up....?
Andre
#44
Nov1-10, 05:50 AM
PF Gold
Andre's Avatar
P: 5,458
Considering this interaction of the Venus atmosphere and losing water, the pre-supposition here is that the current condition is steady state for (most of) the existance of the planet, i.g. many billiards years.

However, if the genesis of the planet resembled that or Earth, having roughly comparable distributions of the elements, one would observe that the amount of carbon in the Venus atmosphere is close to the same order of magnitude of the total estimate amount of carbon on earth. But how did all that carbon get in the atmosphere?

So how about the total amount oxygen? We could not dismiss the amount of oxygen in the CO2 of the Venus atmosphere compared to the total amount of oxygen of the planet, could we? So is it far fetched to presume that the some oxygen in the atmosphere has been in the water of Venus previously?

So again, why that dense CO2 atmosphere? Given the geological past of the planet, with the assumed catastrophical overturning of the surface 0.5 GA ago, the very active volcanism in the past, the extreme surface temperatures of the past, could it be that this dense atmosphere is the result of those processes, i.g. outgassing and burning most of the carbon that used to be in the lithosphere?

Also if Venus was an eartlike rotating planet in the past ( Correia et al 2004) could it be that it had a magnetic field at that time?

But the point is that Venus was likely completely different in the past, so you can't draw conclusions from present states, assuming that it was equal in the past.
Jon Richfield
#45
Nov1-10, 02:48 PM
P: 258
Quote Quote by billiards View Post
Atmospheric stripping by the solar wind on Venus preferentially strips helium, hydrogen, and oxygen....

The point is, perhaps the magnetosphere is important to us (and all life) here on Earth, as it has stopped our planet from drying up....?
Fair enough billiards, but even if this were the start of our permanent loss of any terrestrial magnetic field (which is of course possible, though no one has been seriously arguing it afaik) it seems as though we are talking about GY orders of magnitude before things were likely to get really tight.

Now, as some of you might well know, I am inclined to take a long view about worrying about things, but so far this does not look like something to worry about yet. If the actual period of negligible magnetic field is to be mere millennia every MY or so, then we had better worry about our sun going red giant first.

Gee... yeah...

Jon


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