Origin of The Earth’s Magnetism

Posted on March 8, 2008 by Rashid Faridi
    • “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.

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

Posted on March 8, 2008 by Rashid Faridi

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 

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A One-Way, One-Person Mission to Mars

Posted on March 8, 2008 by Rashid Faridi


simon_on_top_of_castle_mercurythumbnail.jpg 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.

Source 

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Space Station Ready for New Robot

Posted on March 7, 2008 by Rashid Faridi

A massive robot and Japan’s first room in space are set for delivery to the International Space Station (ISS) next week aboard NASA’s space shuttle Endeavour.

Canada’s two-armed robot, named Dextre for its nimble capabilities, should give astronauts a break from basic repair and maintenance tasks outside of the growing space station. The Japanese Logistics Pressurized (JLP) Module marks the first of three components for that nation’s massive Kibo science lab.

“This flight will be a monumental flight for Japan,” said Tetsuro Yokoyama, operations project deputy manager for Kibo, during a press briefing at Johnson Space Center this week. “We are very close to a long-awaited moment.”

The seven-astronaut STS-123 space shuttle crew, led by commander Dominic Gorie, is slated to launch at 2:28 a.m. EDT (0628 GMT) on March 11 aboard Endeavour. The crew aims to install Japan’s new orbital room in a temporary position on March 14, then begin Dextre’s assembly on March 15.

Meet Dextre

To fit the Canadian Space Agency’s $274-million, 3,440-pound (1,560-kilogram) robot into Endeavour’s payload bay, engineers crafted it into large chunks that spacewalking astronauts could assemble outside of the ISS.

Once astronauts latch each piece in place and attach it to a mobile platform on the space station, Dextre will be able to do many standard tasks with an astronaut or earthbound operators at its controls.

“He’s got huge arms, kind of got like a head up there and a lower torso,” said astronaut Rick Linnehan, a mission specialist on the STS-123 mission, comparing it “Gigantor,” a famous cartoon robot. “It allows us to … increase the amount of robotics tasks we do up on station.”

That’s important, NASA officials have said, because spacewalking is risky business for astronauts. The new robot is also expected to give space station crewmembers more time to focus on science and other tasks, they added.

“It’s sitting out there in the harsh environment of space all the time, basically ready to go,” said Daniel Rey, manager for the Dextre project. “It doesn’t require any pre-breathe protocol and it doesn’t require any cleanup. It’s an operational robot that’s pushing the limits of what we can do in space today with robotics.”

Each of Dextre’s seven-jointed arms will possess a “hand” — an orbital replacement unit — backed by a sensor sensitive to less than 1 pound (0.5 kilogram) of force, or about the weight of a small water bottle. The device will use a suite of tools to replace burned-out components outside the ISS, as well as assist spacewalkers with their duties.

Space Closet

Japan’s JLP module will serve primarily as attic space for the three-part Kibo science laboratory when it’s finished some time in 2009. Initially, however, the 9.2-ton cylindrical room will be used to ferry eight systems and science experiment racks to the ISS.

“I feel it’s a little bit small inside,” said Japanese astronaut Takao Doi, noting that the module was slightly larger than a small walk-in closet. “As you know this is a module for storage purposes.” Doi, an STS-123 mission specialist representing the Japan Aerospace Exploration Agency (JAXA), will deliver the new room to the ISS using Endeavour’s robotic arm.

The module, to be followed by a “back porch” exposed to space and a school bus-sized science lab, is part of Japan’s 680 billion yen ($6.6 billion) space station science initiative, JAXA officials have said.

Aside from Dextre and Japan’s module, Endeavour will carry experiments to Europe’s Columbus laboratory module, as well as a testbed to demonstrate a repair method to fix chinked heat-resistant tiles on a shuttle’s heat shield. NASA is also sending up RIGEX — short for Rigidizable Inflatable Get-Away-Special Experiment — that is a small, automated experiment designed to test making inflatable structures in orbit.

source 

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