First Measurement of Magnetic Field In Earth's Core

An anonymous reader writes "A University of California, Berkeley, geophysicist has made the first-ever measurement of the strength of the magnetic field inside Earth's core, 1,800 miles underground. The magnetic field strength is 25 Gauss, or 50 times stronger than the magnetic field at the surface that makes compass needles align north-south. Though this number is in the middle of the range geophysicists predict, it puts constraints on the identity of the heat sources in the core that keep the internal dynamo running to maintain this magnetic field."

Comments

The final sentence

[Amorymeltzer]

"I still find it remarkable that we can look to distant quasars to get insights into the deep interior of our planet," Buffett said.

I don't think we need more reasons to study space, but here's one anyway. Studying quasars billions of light years away helps us understand the Earth's magnetic field - what more support do we need for the value and interrelatedness of any and all scientific research?

Re:The final sentence

[MoonBuggy]

Wait, we need support now?

Re:The final sentence

[$RANDOMLUSER]

They were simply using the quasars as fixed points of reference, the way a sextant uses the horizon.

Re:The final sentence

[davester666]

Of course, now that we've measured it, the field strength has changed...

Re:The final sentence

[PPH]

Thank goodness we have organizations like the National Science Foundation to support this kind of work.

Re:The final sentence

[DriedClexler]

"Scientists use quasars like a drunk uses a lamppost: for support rather than illumination."

Neato

[wizardforce]

He used the precession effect on Earth's core caused by the moon to calculate how much the magnetic induction deviated the calculated value of precession from the measured value. Basically, the field imparts a force that counteracts the precession of the inner core that is measurable. It's pretty clever how he was able to calculate the strength of the magnetic field the way he did:

He realized, however, that the tug of the moon on the tilt of the earth's spin axis could provide information about the magnetic field inside. This tug would make the inner core precess – that is, make the spin axis slowly rotate in the opposite direction – which would produce magnetic changes in the outer core that damp the precession. Radio observations of distant quasars – extremely bright, active galaxies – provide very precise measurements of the changes in the earth's rotation axis needed to calculate this damping.

"The moon is continually forcing the rotation axis of the core to precess, and we're looking at the response of the fluid outer core to the precession of the inner core," he said.

By calculating the effect of the moon on the spinning inner core, Buffett discovered that the precession makes the slightly out-of-round inner core generate shear waves in the liquid outer core. These waves of molten iron and nickel move within a tight cone only 30 to 40 meters thick, interacting with the magnetic field to produce an electric current that heats the liquid. This serves to damp the precession of the rotation axis. The damping causes the precession to lag behind the moon as it orbits the earth. A measurement of the lag allowed Buffett to calculate the magnitude of the damping and thus of the magnetic field inside the outer core.

Re:Neato

[crumley]

Nope, the precession of equinoxes is related to bulging of the Earth's equator.

So, is our goose cooked?

[Tablizer]

Did they find out when the magnetic dynamo will cool down, running out of steam, leaving the Earth naked to the overly-spicy energy of space; baking our DNA into wispy little snippets of death-inducing mutations; sending all us land-dwelling mammals into a deep, eternal nap; with our limbs and genitals joining a new journey as worm nutrients?

Or, are they still working on that question?

Re:So, is our goose cooked?

[MichaelSmith]

In a thousand years or so, fossil fuels will be gone. In a hundred thousand years the biosphere will be totally run down by human exploitation, unless we manage it end to end as a farm. In a billion years (or so) the suns output will have changed to move the habitable zone away from the Earth. In five billion years the sun will become a red giant and we will all be toast.

I don't know when we will lose the magnetic field but if it happens anywhere after a thousand years from now we should be able to build our own. If we can't then we are not much of an intelligent species and we will be heading for extinction anyway.

Re:So, is our goose cooked?

[PPH]

and we will all be toast.

Toast, pâté de foie gras. You're making me hungry.

Re:So, is our goose cooked?

[gman003]

The dynamo has been running for about 3.5 billion years. Thus, from simple math and statistics (and the fact that we are not currently observing the beginning or end of the dynamo), I can state with 99.999% accuracy that the field will remain for at least thirty-five thousand years (and no more than 35 trillion years). Thus, we don't need to worry about that right now.

Re:So, is our goose cooked?

[Tablizer]

That's the kind of thinking the dinosaurs used.

Re:So, is our goose cooked?

[Waccoon]

No worries. By then, I doubt we'll be the species, anyway.

Re:So, is our goose cooked?

[ikeman32]

In a thousand years or so, fossil fuels will be gone. In a hundred thousand years the biosphere will be totally run down by human exploitation, unless we manage it end to end as a farm. In a billion years (or so) the suns output will have changed to move the habitable zone away from the Earth. In five billion years the sun will become a red giant and we will all be toast.

I don't know when we will lose the magnetic field but if it happens anywhere after a thousand years from now we should be able to build our own. If we can't then we are not much of an intelligent species and we will be heading for extinction anyway.

If the human race manages to survive another thousand years without vaporizing ourselves or pissing off some extraterrestrial race first.

Re:Measurement? What measurement?

[wizardforce]

Can you name any measurement that isn't indirect in some way? To measure a magnetic field, you're actually observing something that the field affects such as a Hall effect magnetometer which measures the voltage potential induced by a magnetic field in a conductor or a SQUID magnetometer which measures a current accross a josephson junction

Re:Fucking Magnets

[Enokcc]

Does it explain how they work?

No, but Richard Feynman does.

Re:Measurement? What measurement?

[adavies42]

and worse than that, you're doing it with your eyes! when's the last time you had your vision checked? seen any good optical illusions recently? eyes are terribly unreliable things....

Re:The uncited Nature paper

[maxwell demon]

The way the submitted stories seem to overwhelmingly favor paywalls, and when I see that a thoughtful person usually finds and posts a relevant link with no such restrictions, I can't help but wonder if Slashdot has some kind of "kickback" arrangement with several paywall sites.

For scientific journals, almost all of them are behind paywalls, especially the high-profile ones. So unless the scientists put the articles on arXiv (which not all do; also some journals may not allow that) or choose one of the few open-access journals (but as I said, the high-profile journals aren't, and for your career it's important to get publications in those), those articles will always be behind paywalls.

Re:The uncited Nature paper

[Chris Burke]

The way the submitted stories seem to overwhelmingly favor paywalls, and when I see that a thoughtful person usually finds and posts a relevant link with no such restrictions, I can't help but wonder if Slashdot has some kind of "kickback" arrangement with several paywall sites.

I love how this theory popped up in a story where the opposite happened: The submitted story's link is to a free news article, while a thoughtful user provided the paywall-blocked original paper. /. stories usually, though not always, mention when a link is behind a paywall or even a free-registration-wall. And I've noticed no bias towards paywall blocked sites. /.ers don't RTFA to begin with, how much are they expecting to make off people going to the paywall-protected site then signing up for a subscription (which in the hypothetical kickback situation would surely be the requirement for earning the kickback)?

But hey, maybe it's true, I don't know. I just think it's funny that you didn't bring it up in a story that's the opposite.

Reporters attempted to contact David Innes

[Chris Mattern]

...for comment, but he was unavailable.

Re:Measurement? What measurement?

[Urkki]

Can you name any measurement that isn't indirect in some way?

"Indirect" can be thought to mean "by observing other natural phenomena", opposed by "direct" meaning "observing only phenomena happening with specifically built measurement device".

Directness starts at the point where everything is specifically constructed for the measurement, and wouldn't be happening without the measurement device or measurement operation.

Like, measuring amount of light by using an artificial sensor that gives out well defined signal would be a direct measurement. The signal from the sensor exists and is valid only when sensor is set up to receive light and send the signal. Also the correlation between amount of light and signal value can be adjusted by the design of the measuring device.

On the other hand, measuring amount of light by measuring sugar content and flow in a tree's sap would be an indirect measurement of amount of light. The amount of sugar in the sap isn't affected by it being measured, it's a "natural" occurrence. Also correlation between signal value (amount of sugar) and amount of light can't be adjusted by adjusting the measuring device. it's But it could well be a direct measurement of amount of sugar in the sap.

Above distinction is meaningful, so I'd say it's at least better than what you apparently propose (that all measurement is indirect, there's no direct measurement of anything).