What's Wrong with Earth's Magnetic Field

What’s Wrong with Earth’s Magnetic Field? – The South Atlantic Anomaly

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From satellites malfunctioning to strange flashing lights seen by astronauts on the International Space Station, there is something odd happening in certain parts of space close to earth and the cause of these could have wide-ranging impacts on all of us in the future.

In February 2016, the state-of-the-art Japanese X-ray observatory ‘Hitomi’ launched atop a Mitsubishi H-IIA rocket, into a circular orbit 570 kilometres above the Earth. Its mission was to study high-energy processes like black holes and supernovae within clusters of distant galaxies. But after a month of successful operations, the Japanese Space Agency (JAXA) announced on March 26th that they had suddenly lost communication with ‘Hitomi’. Worse: the satellite was in an uncontrolled spin. Attempts by the internal guidance system to correct the rotation only made the problem worse: turning faster and faster until the solar panels broke away, leaving ‘Hitomi’ without power.

On 28th April 2016 after a month of attempts to re-establish communication, JAXA declared the $273 million space observatory lost. But what caused ‘Hitomi’s disastrous demise?

The answer lies in the peculiar pattern of radiation which surrounds the Earth, ‘discovered’ in 1958 by the first US satellite. The American Physicist James Van Allen proposed fitting ‘Explorer 1’ with a Geiger counter attached to a small tape recorder, to measure radiation levels above the atmosphere. Sure enough, ‘Explorer 1’ observed distinct patterns of radiation during its 111-day mission. These became known as the ‘Van Allen Belts’: doughnut-shaped fields of energized particles emitted from the sun and trapped by the Earth’s magnetic field.

In fact, the radiation belts were discovered by Sputnik 2 just over two months before the American Explorer 1. However, due to Sputnik’s trajectory being over foreign territory and the secrecy around the mission, it meant that when the signals were picked up by the Australians, the two sides refused to talk to each other and the Australians refused to pass the data on. When the soviets did get the data they mistakenly thought the spikes in radiation were a result of a recent solar flare and by the time they had figured out the real reason, the American Van Allen team had announced the discovery.

There are two main concentrations of radiation surrounding the Earth: an ‘Inner Radiation Belt’ made up of mostly energized protons, that peaks at around 2900 kilometres, and an ‘Outer Radiation Belt’, mostly consisting of electrons, that peaks at an altitude of around 16,000 kilometres.

The ‘Van Allen belts’ are responsible for auroras such as the Northern and southern lights where they met with the Earth’s atmosphere around the magnetic poles and channel charged particles into the upper atmosphere. Its here that they react with the atmospheric gases and form the colourful displays. The most common auroral color, a pale yellowish-green, is produced by oxygen molecules located about 100km above the earth. Rare, all-red auroras are produced by high-altitude oxygen, at heights of up to 330km. Nitrogen produces blue or purplish-red aurora.

But orbital surveys also revealed another large area where strong radiation dips down to just 200 kilometres above the Earth’s surface, over a continent-sized area centred above the Atlantic Coast of South America. This is known as the ‘South Atlantic Anomaly’: a ‘Cosmic Bermuda Triangle’ and it’s this that causes the strange effects on both the human body and robotic spacecraft.

 

In the 1960s and 1970s, spacecraft in orbit relied on early computer chips with much larger transistor sizes, and less sensitivity to the bombardment of charged particles. This electronic ‘toughness’ was especially important for the Apollo missions, which had to cross the Van Allen belts and leave the protection of Earth’s magnetic field.

But during the missions, the astronauts reported seeing spots and streaks of light, which continued to flash even when they closed their eyes. These visual effects are called ‘phosphenes’, and a 2006 survey of astronauts found 47 of 59 respondents had experienced them, with some even reporting that the lights disturbed their sleep.

Although humans haven’t crossed the Van Allen belts since December 1972, all spacecraft that pass through the South Atlantic Anomaly experience an increased dose of radiation: up to 1000 times usual levels for Low Earth Orbit. To deal with this, the International Space Station is fitted with shielding that protects astronauts from some of the increased radiation when passing through the anomaly. Even so, the crew on the ISS each wear a personal ‘dosimeter’, and electronic devices often suffer failures, known as ‘Single Event Upsets’

These are more common with consumer-grade electronics, which are built to less demanding specifications than space or military-grade components which are radiation hardened. Since the Space Shuttle missions, astronauts have reported laptop computer failures over the South Atlantic. Fortunately, the fix is usually just a simple reboot.

One way to shield against high energy charged particles it to use water, yep good old fashioned water makes an excellent shield against ions, electrons and protons due to it’s high hydrogen content. Some astronauts have taken to lining their sleeping area with water bags and even their dosimeters to reduce their total exposure number to get longer or more frequent missions, but of course at their own risk of greater radiation exposure.

However, Space Telescopes like Hubble depend on highly sensitive electronics to capture light from distant galaxies. As Hubble passes through the South Atlantic Anomaly, operators routinely switch off imaging sensors to avoid damaging them. However, one of Hubble’s cameras – the Wide Field Camera 3 (WFC3) – can still function in this portion of the orbit: but these images still register the characteristic speckling of radiation artefacts.

‘Hitomi’s’ light-gathering sensors were ultimately found to be the cause of the failure-cascade that led to the loss of the Japanese satellite. When passing through the South Atlantic Anomaly, The star tracker which is used to orientate the craft with a known fixed point, suffered a series of glitches: causing the satellite to switch to backup gyroscopic instrumentation, which also then failed. Being on the opposite side of Earth from Japan, and out of direct communication with mission control, the error was only discovered when it was too late.

To avoid similar losses in future, space agencies are pursuing two strategies: to better understand the South Atlantic Anomaly, and to make satellite electronics more resilient to the effects of radiation as they pass through the danger zone.

But the South Atlantic Anomaly is not a stationary phenomena, Since 1958 scientists have observed that the South Atlantic Anomaly has been increasing in size: and is also gradually moving Northward and Westward. This in line with both the north and south poles which are constantly moving around. Over the last 150 years the north pole has moved over 1000km and has recently accelerated to 40km per year and The magnetic south pole is now over 1000km away from the Geographic South pole.

But there isn’t just one anomaly either, in fact, there are many smaller ones scattered around the globe.

The European Space Agency is currently mapping these changes with the ‘SWARM’ mission, which launched three small satellites into polar orbits. Two of the SWARM satellites orbit side-by-side at an altitude of 450 kilometres and one orbits at a higher altitude of 530 kilometres. SWARM has tracked fluctuations in the Earth’s magnetic field since 2014: and the data has revealed strange ‘weather systems’ deep beneath our feet, that may be to blame for the spreading footprint of the South Atlantic Anomaly.

Beneath 2900 kilometres of crust and mantle, our planet’s iron core is in two parts. A central core of solid iron-nickel alloy about the size of the moon at 4500 degrees centigrade: as hot as the surface of an orange star like Arcturus, and yet solid due to the immense pressure of 50 million pounds per square inch bearing down on it. The second outer core is molten and about the size of mars and fully envelopes the inner one. As the planet spins, Its the movement of this molten metal outer core which is responsible for the generation of the magnetic field. The outer core is molten iron and as a liquid it is affected by the Coriolis forces that come from the spinning earth.

These forces create chaotic movement in the outer core, much like the weather in our atmosphere, also like our weather, this outer core weather is driven by heat but instead of heat from the sun ,this is heat from the inner core. This sets up massive convection currents, combined with the swirling effects of the Coriolis forces its creates weather systems and storms within the molten outer core.

These storms create new temporary magnetic poles that can be the opposite to the surrounding area. This is what the South Atlantic Anomaly is, it is a pole reversal and as such, it negatates the effect of the magnetic field around it, weakening it and allowing the charged particles to come much closer to the earth. Like atmospheric storms ,these, outer core storms can also merge and become larger, which how the South Atlantic Anomaly is believed to have grown in strength.

The SWARM mission has also identified a molten iron ‘jet-stream’ in the Outer Core, flowing westwards beneath Alaska and Siberia at a speed of 50 kilometres per year. Although that may not sound like a lot, this dense flow of iron takes a huge amount of energy to move, and is estimated to be hundreds of millions of years old.

This increasing chaotic behaviour in the outer core is thought to be the prelude to a complete pole reversal, something that has happened hundreds of times before in earth’s history, about every 250,000 years. The last time it happened was over 750,000 years ago, so it looks like we are due for another anytime now. Although a pole reversal takes several thousand years to complete, during this time the earth’s magnetic field would weaken considerably and might consist of multiple north and south poles spread anywhere around the globe.

A weaker magnetic field would bring charged particles closer to earth which could create ozone holes like that which formed over the south pole a few decades ago. This would increase the level ultra violet light and increase the risk of things like skin cancer. It would also leave us more susceptible to solar storms which could wreak havoc with the worlds electrical power grid.

By finding more ‘weather patterns’ in the Core, SWARM will help to predict the future shape and behaviour of Earth’s magnetic field.

In any case, building tougher satellites is set to be big business in the coming decades as we see a surge in the number of ‘small-sats’. By launching networks of miniaturised satellites into low orbits, government and commercial satellite operators aim to replace heavy and expensive Geostationary satellites, at a fraction of the cost. Small-sats usually orbit below most of the radiation of the Inner Van Allen belt, and avoid the long-term degradation of electronics found on Geostationary satellites which operate within the outer Van Allen Belt. However, small-sats have another problem: they frequently pass through the South Atlantic Anomaly.

One company working on the problem is Thales Alenia Space, a French-Italian aerospace company who are Europe’s largest satellite manufacturer. They are pioneering the use of gallium nitride-on-silicon chips, which operate at higher voltages and temperatures than regular silicon chips, offering increased protection against radiation.

In commercial applications, the loss of several nodes in a satellite network would be an inconvenience. However, if military satellite operators transition from Geostationary to Low Earth Orbit small-sats, then the effects of the South Atlantic Anomaly could introduce a significant vulnerability especially after a solar storm.

Whichever way we go, what is happening deep below our feet is going affect what happens high above us and ultimately what happens here on the surface of the earth, so we need to take steps to be prepared.

What’s your thoughts about the growing instability in the outer core and what do you think we should be doing to counter its possible effects on our way of life, let me know in the comments.

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Paul Shillito
Creator and presenter of Curious Droid Youtube channel and website www.curious-droid.com.

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