Magnetic Field of Earth

Earth’s Inconstant Magnetic Field Our planet’s magnetic field is in a constant state of change, say researchers who are beginning to understand how it behaves and why.

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December 29, 2003: Every few years, scientist Larry Newitt of the Geological Survey of Canada goes hunting. He grabs his gloves, parka, a fancy compass, hops on a plane and flies out over the Canadian arctic. Not much stirs among the scattered islands and sea ice, but Newitt’s prey is there–always moving, shifting, elusive.

His quarry is Earth’s north magnetic pole.

At the moment it’s located in northern Canada, about 600 km from the nearest town: Resolute Bay, population 300, where a popular T-shirt reads “Resolute Bay isn’t the end of the world, but you can see it from here.” Newitt stops there for snacks and supplies–and refuge when the weather gets bad. “Which is often,” he says.

Right: The movement of Earth’s north magnetic pole across the Canadian arctic, 1831–2001. Credit: Geological Survey of Canada. [more]

Scientists have long known that the magnetic pole moves. James Ross located the pole for the first time in 1831 after an exhausting arctic journey during which his ship got stuck in the ice for four years. No one returned until the next century. In 1904, Roald Amundsen found the pole again and discovered that it had moved–at least 50 km since the days of Ross.

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The pole kept going during the 20th century, north at an average speed of 10 km per year, lately accelerating “to 40 km per year,” says Newitt. At this rate it will exit North America and reach Siberia in a few decades.

Keeping track of the north magnetic pole is Newitt’s job. “We usually go out and check its location once every few years,” he says. “We’ll have to make more trips now that it is moving so quickly.”

Earth’s magnetic field is changing in other ways, too: Compass needles in Africa, for instance, are drifting about 1 degree per decade. And globally the magnetic field has weakened 10% since the 19th century. When this was mentioned by researchers at a recent meeting of the American Geophysical Union, many newspapers carried the story. A typical headline: “Is Earth’s magnetic field collapsing?”

Probably not. As remarkable as these changes sound, “they’re mild compared to what Earth’s magnetic field has done in the past,” says University of California professor Gary Glatzmaier.

Sometimes the field completely flips. The north and the south poles swap places. Such reversals, recorded in the magnetism of ancient rocks, are unpredictable. They come at irregular intervals averaging about 300,000 years; the last one was 780,000 years ago. Are we overdue for another? No one knows.

Left: Magnetic stripes around mid-ocean ridges reveal the history of Earth’s magnetic field for millions of years. The study of Earth’s past magnetism is called paleomagnetism. Image credit: USGS. [more]

According to Glatzmaier, the ongoing 10% decline doesn’t mean that a reversal is imminent. “The field is increasing or decreasing all the time,” he says. “We know this from studies of the paleomagnetic record.” Earth’s present-day magnetic field is, in fact, much stronger than normal. The dipole moment, a measure of the intensity of the magnetic field, is now 8 × 10²² amps × m². That’s twice the million-year average of 4× 10²² amps × m².

To understand what’s happening, says Glatzmaier, we have to take a trip … to the center of the Earth where the magnetic field is produced.

At the heart of our planet lies a solid iron ball, about as hot as the surface of the sun. Researchers call it “the inner core.” It’s really a world within a world. The inner core is 70% as wide as the moon. It spins at its own rate, as much as 0.2° of longitude per year faster than the Earth above it, and it has its own ocean: a very deep layer of liquid iron known as “the outer core.”

Right: a schematic diagram of Earth’s interior. The outer core is the source of the geomagnetic field.

Earth’s magnetic field comes from this ocean of iron, which is an electrically conducting fluid in constant motion. Sitting atop the hot inner core, the liquid outer core seethes and roils like water in a pan on a hot stove. The outer core also has “hurricanes”–whirlpools powered by the Coriolis forces of Earth’s rotation. These complex motions generate our planet’s magnetism through a process called the dynamo effect.

Using the equations of magnetohydrodynamics, a branch of physics dealing with conducting fluids and magnetic fields, Glatzmaier and colleague Paul Roberts have created a supercomputer model of Earth’s interior. Their software heats the inner core, stirs the metallic ocean above it, then calculates the resulting magnetic field. They run their code for hundreds of thousands of simulated years and watch what happens.

What they see mimics the real Earth: The magnetic field waxes and wanes, poles drift and, occasionally, flip. Change is normal, they’ve learned. And no wonder. The source of the field, the outer core, is itself seething, swirling, turbulent. “It’s chaotic down there,” notes Glatzmaier. The changes we detect on our planet’s surface are a sign of that inner chaos.

They’ve also learned what happens during a magnetic flip. Reversals take a few thousand years to complete, and during that time–contrary to popular belief–the magnetic field does not vanish. “It just gets more complicated,” says Glatzmaier. Magnetic lines of force near Earth’s surface become twisted and tangled, and magnetic poles pop up in unaccustomed places. A south magnetic pole might emerge over Africa, for instance, or a north pole over Tahiti. Weird. But it’s still a planetary magnetic field, and it still protects us from space radiation and solar storms.

Above: Supercomputer models of Earth’s magnetic field. On the left is a normal dipolar magnetic field, typical of the long years between polarity reversals. On the right is the sort of complicated magnetic field Earth has during the upheaval of a reversal. [more]

And, as a bonus, Tahiti could be a great place to see the Northern Lights. In such a time, Larry Newitt’s job would be different. Instead of shivering in Resolute Bay, he could enjoy the warm South Pacific, hopping from island to island, hunting for magnetic poles while auroras danced overhead.

Sometimes, maybe, a little change can be a good thing.

Source: Nasa Website 

Origin of The Earth’s Magnetism

• “Diurnal motion is due to causes which have now to be sought, arising from magnetick vigour and from the confederated bodies.”

Blackett’s Proposal

It is an uncanny fact that the Earth’s magnetic axis is close to its rotation axis–that the magnetic poles, where the magnetic force points straight down, are quite close to the geographical ones. William Gilbert saw it as evidence that rotation and magnetism arose from the same source: Gilbert thus believed the Earth rotated because it was magnetic. P.M. Blackett, who won the 1948 Nobel prize for his work on cosmic rays, seriously considered the opposite possibility–that the Earth was magnetic because it rotated around its axis. Blackett at one time suggested that perhaps a new universal phenomenon existed–that any rotating object was intrinsically magnetized.

At first this did not seem such a wild idea. Electrons and protons, for instance, do have an intrinsic “spin” giving them properties like those of a rotating solid object, and they also have an intrinsic magnetization, making them tiny magnets, lined-up with their spin axes. In ordinary materials, such atomic magnets point in all possible directions, so that their effects cancel.

But concerning the Earth, Blackett guessed wrong. Experiments with spinning objects, which by his theory should have produced measurable magnetization, showed none. Later observations also showed that during the last tens of millions of years, the magnetic polarity of the Earth reversed many times, something that Blackett’s prediction would never allow.

The core of the Earth

The Earth’s Core

The way earthquake waves spread tells us that the Earth has at its center a dense liquid core, of about 1/2 the radius of the Earth–and inside that, a solid inner core. It is widely believed this core is made up of molten iron, perhaps mixed with nickel and sulfur. The density seems appropriate, and iron, which among all elements has the most stable nucleus, is abundant in the universe. It concentrated in the Earth’s core because it is heavy–the same reason that, when it is extracted from its ores, it sinks to the bottom of the blast furnace. Energy is the currency with which most processes in nature must be paid for. The Earth’s magnetism is no exception, and its energy seemes to come from fluid motions in the Earth’s core, from circulating flows that help get rid of heat produced there. In a similar way, our weather is driven by circulating air flows that help cool the ground, where much of sunlight is absorbed.

Scientists are still not sure about what provides the heat in the Earth’s core. It might come from some of the iron becoming solid and joining the inner core, or perhaps it is generated by radioactivity, like the heat of the Earth’s crust. The flows are very slow, and the energy involved is just a tiny part of the total heat energy contained in the core.

So the molten metal is believed to be circulating. By moving through the existing magnetic field, it creates a system of electric currents, spread out through the core, somewhat like Faraday’s disk dynamo, discussed earlier. Currents create a magnetic field–a distribution of magnetic forces–and the essence of the self-sustaining dynamo problem is to find solutions such that the resulting magnetic field is also the input field required for generating the current in the first place.

Actually, that is only the lowest level of the problem, in which one is free to prescribe the motions. To solve the full problem, we also need information about the heat sources, and these sources must be able to drive motions which also solve the dynamo problem.

Such problems are not easy. They involve intricate mathematics and are not yet fully solved. Only the roughest ideas in their solutions can be outlined here.

The Sun’s Magnetism

One limitation, related to the failure of Blackett’s theory, is that any electric circuit rotating like a solid body will not produce “dynamo currents.” Even if part of the circuit follows the axis of rotation, and can therefore be viewed as non-rotating, solid rotation will not create any currents. An essential feature of the Faraday disk dynamo is that part of its circuit is outside the disk, not sharing its rotation. The rotation of the Sun around its axis, therefore, does not by itself contribute to its magnetism. What is important in this case is that the Sun does not rotate like a solid ball. Its equator has a shorter rotation period than higher latitudes– about 25 days for the equator, 27 days for latitude 40 degrees (the Earth meanwhile moves some distance around the Sun, so from here the period seems to be 27 and 29 days). If Earth rotated that way, Florida (for instance) would soon pull away from the rest of the US, into the Atlantic Ocean. Such an uneven motion, deforming the surface, can drive a dynamo, and in the Sun’s case, it is indeed believed to be the source of sunspot magnetism.

Dynamo Theory

Before mathematicians tackle a complex problem, they try out simple solutions (joke about a mathematician’s model of milk production: “Assume a spherical cow of radius R, uniformly filled with milk… “). No such luck here: early in the game, in 1934, Thomas G. Cowling in England proved that any self-sustaining dynamo in the Earth’s core cannot have an axis of symmetry. Walter Elsasser, at the University of Utah (later at Johns Hopkins) launched in the 1940s a frontal attack on the full 3-dimensional problem. He got nowhere: the equations became more and more intricate and complicated the further one went into the details. Others had similar experiences. Only in 1964 did Stanislaw Braginsky in Russia publish the first valid solutions, by assuming that the field was almost axially symmetric and calculating its small deviations from symmetry.

The solution of the full problem, including heat flow, is much harder. Not only are we unsure of the source of heat, but any motions caused by it are greatly modified by the Earth’s rotation. That modification is a major feature of large-scale motions in the atmosphere, causing hurricanes and storm systems to swirl in their characteristic ways. Eugene Parker in 1955 proposed a mechanism by which such swirling, in the rising flows of the Sun’s atmosphere, could create dynamo fields.

As viewed from above, the swirling direction of storms in the atmosphere is always counterclockwise north of the equator and clockwise south of it. Such asymmetry is also expected in rising flows in the Earth’s core, and Steenbeck et al., in Germany, showed in 1966 that thanks to it, disordered convection patterns can indeed produce an average “dynamo field. ” That became known as the “alpha effect, ” because it involved a mathematical quantity denoted by the Greek letter a (alpha)–but the details are far too complicated to be described here.

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For some current work, simulating the dynamo on a computer, see web site by Gary Glatzmeier and Paul Roberts, here. Glatzmaier and collaborators have conducted some interesting simulations of the dynamo process, with realistic behavior, although limitations of computer speed forced them to simplify the properties of the liquid core. A Japanese team of Takahashi et al (Science, 309, p. 459-61, 15 July 2005) has more recently used one of the worlds fastest supercomputers to carry out a similar calculations assuming a much lower fluid viscosity in the core, much closer to the actual one. The behavior seems even closer to the one observed.source

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Fears of Big Freeze as Scientists Detect Slower Gulf Stream

The ocean “engine” that helps to drive the warm waters of the Gulf Stream and keeps Britain relatively mild in winter has begun to slow down, say scientists.

Measurements of ocean currents in the North Atlantic reveal that they have weakened by about 30 per cent since 1992. The findings, published in the journal Nature, fit computer predictions of what would happen when Greenland glaciers begin to melt because of global warming. The models suggest that extra freshwater released into the North Atlantic could weaken ocean currents and even shut down the Gulf Stream.

Britain benefits from the enormous amounts of heat - equivalent to the output of a million power stations - carried from the Caribbean by the Gulf Stream and the North Atlantic Drift, and a tailing off in these currents could have a major impact on the country’s climate.

Scientists estimate that the detected 30 per cent weakening of the Atlantic currents could lead to a fall of about 1C in Britain’s average temperatures over the next 20 years.

They also warn that the weakening could be the first signs of an accelerating trend that could eventually lead to a more drastic change, including a complete shutdown of the currents. If this were to happen, average temperatures in Britain could fall by between 4C and 6C, leading to winter temperatures similar to Newfoundland in Canada, which is on the same latitude as the UK but does not benefit from the Gulf Stream.

Professor Harry Bryden, of the National Oceanography Centre at the University of Southampton, said the ocean currents of the North Atlantic acted as a conveyor belt that carried warm water at the surface in one direction and transported cold, deep-water currents in the other.

“It is a massive system that includes the Gulf Stream and it carries heat northward out of the tropics into the northern Atlantic, warming the atmosphere and helping to provide northern Europe with a moderate climate,” Professor Bryden said.

For the past 50 years, oceanographers have measured the strength of these currents along a stretch of the North Atlantic situated at a latitude of 25 degrees north of the equator, from Florida in the west to the African coast in the east.

When they analysed that rate of ocean flow - measured in Sverdrups (Sv), or a million tons of water flowing per second - they found that in 1992 it was about 20Sv, but in 2004 it had fallen to 14Sv. “In previous studies over the past 50 years, the overturning circulation and heat transport across 25 degrees north were reasonably constant. We were surprised that the circulation in 2004 was so different from previous estimates,” Professor Bryden said.

The study used data from an array of instruments anchored at 22 moorings, nine of which are positioned east of the Bahamas, four in the mid-Atlantic and nine across the continental slope of east Africa. Each mooring is anchored to the seabed on wires 5,000 metres (16,400ft) long, and holds instruments that continuously record salinity, temperature, pressure and current flow. Stuart Cunningham of the National Oceanography Centre said: “Continuous monitoring could alert us to potential rapid climate change.”

SORCE:http://www.commondreams.org 

A One-Way, One-Person Mission to Mars

Will humans ever really go to Mars? Let’s face it, the obstacles are quite daunting. Not only are there numerous, difficult, technical issues to overcome, but the political will and perseverance of any one nation to undertake such an arduous task just can’t be counted on. However, one former NASA engineer believes a human mission to Mars is quite doable, and such an event would unify the world as never before. But Jim McLane’s proposal includes a couple of major caveats: the trip to Mars should be one-way, and have a crew of only one person.McLane worked at NASA for 21 years before leaving in 2007 to work for a private engineering firm. Being able to look from afar at NASA’s activities has given him a new perspective, he says.But McLane was still at NASA when he originally had an idea for a one-way, one-person mission to Mars. He calls his proposal the “Spirit of the Lone Eagle,” in deference to Charles Lindbergh’s solo flight from New York to Paris in 1927.

McLane’s idea came from his acquaintance with a Russian cosmonaut. “I noticed the cosmonaut seemed to be a slightly different type of person than the American astronaut,” McLane said. “Cosmonauts are primarily pilots, and like test pilots, they are very focused on getting the job done. The current American astronauts are picked for things such as their speaking ability and social skills, and most of them have advanced degrees. But the cosmonaut struck me as an adventurous, get-things-done-type person, like our original astronauts back in the 1960’s.”

A return to the “get it done” attitude of the 1960’s and a goal of a manned landing within a short time frame, like Apollo, is the only way we’ll get to Mars, McLane believes. Additionally, a no-return, solo mission solves many of the problems currently facing a round-trip, multiple person crew.

“When we eliminate the need to launch off Mars, we remove the mission’s most daunting obstacle,” said McLane. And because of a small crew size, the spacecraft could be smaller and the need for consumables and supplies would be decreased, making the mission cheaper and less complicated.

While some might classify this as a suicide mission, McLane feels the concept is completely logical.

“There would be tremendous risk, yes,” said McLane, “but I don’t think that’s guaranteed any more than you would say climbing a mountain alone is a suicide mission. People do dangerous things all the time, and this would be something really unique, to go to Mars. I don’t think there would be any shortage of people willing to volunteer for the mission. Lindbergh was someone who was willing to risk everything because it was worth it. I don’t think it will be hard to find another Lindbergh to go to Mars. That will be the easiest part of this whole program.” - universetoday

I’ve heard the theory that one or more unnamed astronauts landed on the moon during the Apollo missions and never came back.  The idea is that the astronauts we know were part of an Earth-based simulation at the same time and the capsules we saw land in the ocean were dropped from a jet. This was supposedly done because the radiation in space makes the mission deadly. We haven’t had any manned missions beyond Low Earth Orbit (100 to 1200 miles high) since Apollo, right? I think the ISS is about 240 miles high.

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