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Episode 25: The Magnetic Pole Shift

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Recap: We've discussed the geographic pole shift on this podcast, now we address the other kind - could Earth's magnetic pole shift, flip, or have something bad happen to it in 2012?

Solution to Episode 23's Puzzler: The solution to the first part comes directly from Kepler's Third Law, which relates the semi-major axis and the period of a planet's orbit. Since I gave you the period, you can directly calculate the semi-major axis, which Chew did, at 234.9 Sun-Earth distances, known as an Astronomical Unit or A.U.. Chew actually used a 3643-year period ... not sure why ... but the number is very close as he got 236.8 AUs.

The solution to the second part can be figured out by just drawing a picture. Draw an ellipse, and put the sun at one focus. Just stick it off to the side along the long axis. The long, or major axis, is two times the semi-major, and since I just gave you that number, then you can get the major axis to be about 470 AU. I told you that the closest it gets to the sun is Earth's orbit, so the distance between the dot you drew for the sun and the edge of the ellipse on the major axis is 1. 470-1 = 469 AU.

The third part is a bit more complicated. Well, a lot more complicated. Much more complicated than I initially thought. It boils down to our good friend Kepler again who figured this all out over 300 years ago, but it still took me about an hour. You have to do things like using another one of Kepler's equations that isn't talked about very often solving for things like mean anomalies, eccentric anomalies, true anomalies, and other stuff. I'm not going to bore you with the math. The value that I found is that it would spend roughly 2.2 Earth years inside the orbit of Jupiter, meaning that right now it'd be well within Jupiter's orbit and would be about the brightest thing in the sky other than the sun or moon, possibly Venus.

Puzzler: Let's say you're an architect in a reasonable part of the world that is poleward of the Tropics. You're designing a patio for a client, and the client wants the sun on the patio from the autumnal equinox through the spring equinox, but because it's hot in, say, Florida, during the summer, they want the roof or awning to block the sun from the spring through autumnal equinoxes. A typical patio in this area is 4 meters on a side and the awning or roof is three meters from the floor. The question is, how far should the roof extend from the poleward side of the edge of the patio? Include latitude as a variable in your solution.

Q&A: Jay P., AKA Pscheptyck from the SGU message boards, asks: "Just finished listening to Episode 23 and I was wondering, hypothetically speaking, if Planet X were real and on a 3600 year cycle and roughly Earth sized and somehow didn't perturb the asteroid belt, wouldn't it have to have a close enough proximity, at some point, to Jupiter? And if so, shouldn't it have already been pulled into Jupiter's gravitational pull? Or do the Planet Xers have it on some sort of trajectory that brings it close to Earth, but then somehow miss the rest of solar system? Sorry for all the questions, but I do appreciate your time and the quality programming."

The short answer to Jay's question is "Yes and yes."

The longer answer to the first part is that a normal object that is roughly coplanar to the rest of the solar system - meaning that it orbits in the same plane as most everything else - would, at some point, swing by Jupiter unless on the VERY unlikely chance it was in some sort of resonance with Jupiter. What I mean by that is Pluto crosses Neptune's orbit twice during its year. But, because for every three times Neptune goes around the Sun, Pluto goes around twice, the two will never collide.

So, unless on the VERY unlikely chance that Planet X were in a resonance with Jupiter, the two would likely meet at some point over the last 4.5 billion years of history (since Planet X would have crossed Jupiter's path over 2 million times).

Now, I'm not sure if it's "to get around" this issue that they say this because I haven't ever really seen much realistic astronomy-based thinking from the Planet X people, but those who have proposed orbits generally have the Planet X coming from above or below the solar system. It would only come close to the plane of the solar system - conveniently - when it's near Earth.

This is very much a special pleading argument stamped on top of something that has zero evidence for its existence but has a lot of evidence that it doesn't exist, though.

Additional Materials:


Claim: Last month, I did a two-episode series on geographic pole shifts - where Earth's spin axis is significantly rotated somehow in some way that I showed couldn't actually happen. I mentioned in the intro for that episode that the basic idea of a pole shift is not as basic as one may think. Earth actually has two different kinds of poles - a spin axis or set of geographic poles, and a set of magnetic poles. Almost every time you hear people talk about a "pole shift" happening in 2012, they do not specify, so you have to ask for clarity or figure it out through context, but they are two very different things.

In this episode, I'm going to focus on "the other" kind of pole shift, the magnetic pole shift. This is usually less frequently talked about - if that "usually less frequently" phrase makes sense - than the geographic pole shift, but those who do talk about it generally have just as dire predictions.

Background on Earth's Magnetic Field

To talk about this, I need to give some background information on Earth's magnetic field, returning to the format that I started this whole podcast series with - the claim, the background, and the refutation.

Earth has a magnetic field. This is often represented as a bar magnet superimposed roughly along the spin axis with North up and South down. This kind of depiction is actually fairly inaccurate.

First, as discussed from the puzzler of Episode 9, the magnetic pole near Earth's geographic North is actually a magnetic south pole, hence why north compass needles are attracted to it. And vice-versa for the one near the geographic south pole. However, to make things hopefully clearer throughout this episode, this is going to be the only mention of that. When I say "north" from here on out, I mean the magnetic pole near the north geographic pole. It's just easier that way.

Second, field lines don't all connect at the magnetic north and south poles. They sort of dive into Earth's surface near the poles -- I'll post a diagram on this episode's website.

Third, Earth's magnetic poles are not 180° away from each other. The most recent positions that I found were from 2005 for the north pole which put it at 82.7°N 114.4°W, and the south pole was at 64.5°S 137.7°E in 2007. Those are not 180° apart.

But on top of that, the overall field strength varies across the globe, including something called the South Atlantic Anomaly where the field is particularly low which causes the van Allen radiation belts to dip closer to the planet.

The poles also move and the fields change with time. Back in 2009, the North magnetic pole was booking it towards Russia from Greenland at a rate of about 55-60 km per year. The south was moving northwest at a more leisurely 10-15 km/yr.

That's just a discussion of the poles. The overall field strength has been changing ever since we started measuring it over 100 years ago. The overall trend is that it's decreasing, having lost around 6% of its strength since 1900. Not that the change has been linear, the change has changed over time.

If we go back a few hundred years, some of this stuff was known. This is perhaps most evidenced by ship captains needing to update their maps every few years with new magnetic pointings due to the shifting poles. If they didn't, they could be off by several kilometers which is kinda important when you don't want to hit that reef.

The point of all this background of the present-day field is to paint a picture of a dynamic magnetic field. It's not static. We know it changes, we know it moves, we know that it is really complicated and we don't fully understand it. We also know that we MAY actually be approaching a magnetic pole reversal.

Magnetic Pole Flips

Yes, I did effectively say that Earth may be in the mood for a magnetic pole flip. From time-to-time, Earth's magnetic poles have effectively reversed position, where the pole that is near the present-day north geographic pole goes to the south, and vice versa.

This is a very poorly understood process, but the evidence that it's happened in the past is fairly clear when one looks at the alternating polarities of crust on either side of the mid-Atlantic ridge. What this means is that when rock gets heated above a certain temperature - called the Curie point - it will lose any magnetic field recorded in it. When it cools, it will take on the field that it cooled in. Since the Atlantic Ocean is spreading and we can date the rocks on the ocean floor as well as determine their magnetic direction, we can create a map of magnetic reversals over the last 150 million years or so. Going back further in time is a bit more complicated, but it can be done, and the picture that's been built up clearly shows many, many reversals throughout geologic time.

The actual rate at which the reversals happen has by all accounts been shown to be statistically random. There appears to be no pattern in the lengths of reversals, the polarity and lengths, nor the distribution of polarities.

What this means is that ANYONE who says that we are "due" for a reversal is wrong. The idea that we're "due" for one comes from the fact that the AVERAGE length of time that Earth has been at any particular polarity over the last few million years is shorter than the time since the last flip, around 780,000 years ago. So based on that average, we're "due," but since the length of time is statistically random, that average is somewhat meaningless.

The next logical question is probably what causes a flip, before we get into what happens during and how long they take.

The cause is fairly unknown, since the origin and mechanics of Earth's magnetic field are somewhat unknown. The best theory we have is the magnetic dynamo one. This is based on two laws of physics, the Biot-Savart Law and Faraday Induction Law. The first says that moving charges create a magnetic field. This is how electromagnets work. The second says that moving magnetic fields create a current in a conductor. This is how a car's alternator works. So put the two together and you have a perpetuating magnetic field where the moving charge creates a magnetic field and the magnetic field creates a moving charge. So long as we have a conductor, which we do because Earth's outer core is liquid nickel and iron and it moves around due to Earth's rotation, you're going to get a magnet.

Why the field actually flips seems to be inherent in the mechanism of the dynamo in an actual system. Meaning, that when people have tried to simulate the dynamo in a computer or during an actual experiment, the field will become chaotic at times, tangling up due to the chaotic nature of the fluid in the outer core. As it tangles and tries to sort itself out again, it will reverse. It just kinda "happens" in the models, though I'm sure there's something more specific that an expert in this could clue me in on.

My point at this stage, though, is that Earth's field DOES flip. This happens. We don't exactly know why, but the evidence that it does is about as conclusive as things get.

What Happens During a Flip

The next question gets into what happens during a flip and how long it takes. After all, 2012 people say it's going to happen this year. So far in this episode, the 2012 people have been batting 1000. Earth's field changes, it's changing now, the field strength is decreasing, and this may mean that we're leading up to a magnetic pole shift. The problem for 2012ers is that is where their grip on the reality of the situation stops.

Magnetic pole flips don't happen in the sense that you could go to bed one night and wake up in the morning and compass needles would all point the wrong way. Nor does it mean that in the middle of a pole flip our "magnetic shield goes down" and the sun would irradiate the planet. If that were the case, then we would see mass extinctions very well correlated with every pole flip in the past, and there are none.

To start with, almost all estimates are that it takes around 1000-10,000 years for a pole shift to complete from start to finish. So we MAY be in the beginning stages of one now. But we won't really know for another few hundred years.

And during a shift, it's not like the field turns off, rearranges itself for a millennium, and then turns back on in the other direction. During a flip, the field becomes very tangled, and you would have many north and south poles emanating all around the Earth. This would make compass navigation very complicated, and it would likely drop the overall field strength to some fraction like 30%. Note that this is actually the opposite of how magnetic reversals happen on the sun every 11ish years, where the field there increases during a reversal instead of decreases.

At this point in the episode, you're probably wondering where the crazy Coast to Coast clip is, or at least me reading a wacky claim. But that's it, we're at the end of the main segment. Like many things in science, this is a situation where we really don't know nearly as much as we'd like. I can pretty much unequivocally state that the idea that the magnetic pole will suddenly flip on December 21, 2012, is wrong, just as it's wrong that it'll flip any time this year or the next hundred years. The mechanisms proposed - which you really have to dig for and apply much more to the wrong ideas for a geographic pole shift - don't make sense. They include things like the sun's magnetic field flipping ours, it being another magical property of the cloaked Planet X and its tractor beam, getting whopped by an asteroid, and mystical powers.

But, the magnetic field is a complicated thing and we don't really know why it flips, we don't have a really good understanding of what happens during a flip, and we don't really know if we're in the beginning stages of one that will complete within the next 10,000 years.

Provide Your Comments:

Comments to date: 2. Page 1 of 1. Average Rating:

Stuart   Boulder, CO, USA

9:33pm on Wednesday, May 23rd, 2012

Graham - Not as far as I know is this remotely feasible. I would think you'd need to have an electromagnet comparable in strength to Earth's AT the region of Earth that the field is generated. So yeah, while things like MRIs are more powerful than Earth's field, that strength doesn't reach outside the room.

GrahamD   Australia

3:45am on Monday, May 21st, 2012 

I've just finished listening to the episode and found it a good and useful explaination of what is and is not known about the working of the Earths magnetic field.

Now a question. I can vaguely remember a story in which an attempt is made to stop the North Magnetic Pole from moving by using huge iron coils, is this even remotely feasable? And if it is, how much iron would be required?

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