스크랩 지구 자기장 역전 - Forget global warming, worry about the MAGNETOSPHERE

[창조나래]

지구는 치명적인 우주 방사선에 노출되어 있습니다. 지상에 생명이 살 수 있는 것은 지구를 감싸고 있는 보이지 않는 힘, 자기권이 있기 때문입니다. 그런데 이 보호막이 약해지고 있다고 합니다. 남대서양 상공의 방사능 수치는 이미 위험 수위에 달했습니다. 지구자기장은 언젠가는 결국 사라질 것입니다. 단지, 그것이 언제냐가 문제입니다.

우주방사선을 막는 보호막, 지구자기장 자기권은 마치 커다란 우산처럼 태양계 전역으로 끊임없이 쏟아지는 우주방사선을 막아 내고 있습니다. 자기권은 지구자기장이 만든 큰 공기 방울 같은 것으로, 지구 전체를 에워싸고 있습니다. 전하를 띤 태양풍 입자가 지닌 에너지는 인간에게 해를 끼치기에 충분합니다. 지구가 태양이 방출한 하전입자에 정면으로 노출된 상황에서 자기권이 없다면, 조직을 뚫고 들어가 세포에 심각한 피해를 주는 이 고(高)에너지 우주 입자에 모든 생명이 피해를 당하게 될 것입니다. 지구자기장이 약해질수록 우주 방사선은 점점 낮은 고도에까지 영향을 미칠 것입니다. 자기 보호막이 줄어들면 일어날 수 있는 일 중 하나는 과도한 방사선 노출로 말미암은 암 발생률 증가입니다. 방사선은 가장 근본적인 곳, 바로 생명의 설계도 DNA에 피해를 줍니다.

지구보호막이 만들어지는 곳 NASA 고더드 우주비행 센터의 과학자 마리오 아쿠나 박사는 막대자석을 이용한 간단한 실험으로 지구자기장의 기본 구조를 보여줍니다. 자석을 판지 밑에 집어넣은 다음 쇳가루를 조금씩 뿌리면 북쪽에서 남쪽으로 가는 선이 생깁니다. 이것이 지구자기장의 대략적인 형태라 할 수 있습니다. 쇳가루가 막대자석의 N극과 S극 주위에 저절로 정렬하는 것처럼 지구자기장 또한 지구 자기의 남극, 자남에서 분수처럼 뿜어져 나와 지구 주위를 한 바퀴 돈 뒤 다시 지구로 흘러들어 가는데, 이곳이 자북입니다. 과학자들은 지구자기장이 지면에서 5천㎞ 아래 지구 깊은 곳에서 만들어지는 것으로 추정하고 있습니다. 이 힘이 만들어낸 지구 자기권은 태양에서 시속 1.6백만㎞ 이상의 속도로 끊임없이 쏟아지는 과열된 하전입자, 태양풍을 막아냅니다.

자극의 이동과 지구자기장의 변화 자극의 이동은 지오다이너모(geodynamo)의 변동을 의미합니다. 최근 몇 십년 동안, 자극의 이동은 빨라졌습니다. 지난 백년 동안은 1년에 약 10km씩 움직였는데 1970년 이후 가속이 붙어 지금은 1년에 40km씩 이동하고 있습니다. 자극의 이동속도가 빨라진 것이 지구자기장 약화와 어떤 관계가 있을까요? 제레미 블록스햄 교수는 사료에서 얻은 데이터를 바탕으로 지구자기장의 궤적을 완성해 1690년 이후 3백여 년간의 변화를 알아보았습니다. 그 결과, 지난 150년 동안 지구자기장의 세기는 전반적으로 10%가량 감소한 것으로 드러났습니다. 또한, 20세기 이후의 자료를 살펴보면, 남대서양의 자기장 이상 지역이 단순히 다른 지역보다 자기장이 약한 것이 아니라는 사실을 확인할 수 있습니다. 극성이 역전된 것입니다. 남대서양의 자기장 역전 지역의 크기는 점점 커지고 있으며, 이처럼 자기장이 뒤집힌 곳에서는 치명적인 우주 방사선이 지구를 비켜가지 않고 그대로 들어옵니다.

자극 역전이 생태에 미치는 영향 자기장이 약화하는 것은 자기장 역전의 전조입니다. 자기장이 뒤집히면 아래위가 뒤바뀐 지도를 보고 길을 찾는 것과 같은 상황이 발생하는데, 이는 자기장을 나침반, 혹은 지도로 이용하는 동물들에게 치명적인 영향을 미칠 수 있습니다. 우리는 이러한 동물의 대표적인 예로 지구 자력선을 감지하는 박쥐를 꼽지만, 자극의 변동은 훨씬 많은 동물들에게 영향을 끼칩니다. 1980년대 생물학자들은 좌초한 고래와 해저에서 발생하는 갑작스러운 자기 이상 사이의 연관성을 발견했습니다. 자기장이 약해지면 우두머리 고래가 신체에 내재된 GPS를 잘못 해석해 무리를 생명에 위협이 될 정도의 얕은 물로 인도할 수 있다는 것입니다. 이처럼 자기장의 변화는 동물의 위치 파악 능력을 저하할 수 있습니다. 지구자기장은 지구에 살고 있는 생명체가 자기 위치를 파악하는 메커니즘으로, 생존을 위해 꼭 필요한 힘입니다. 자기장 없는 세상은 상상할 수 없습니다. 자극의 소멸은 인간을 비롯한 수많은 동물에게 재앙이 될 수 있습니다.

임박한 지구자기장 역전 과학자들은 지구자기장의 역전이 임박했다고 주장합니다. 그 시기의 예측이 시급합니다. 2010년, 정확한 지구자기권 지도를 그려 향후 자기장의 변화를 예측하고자, 유럽 우주 기구는 ‘스웜’ 위성을 발사합니다. 지구 보호막이 약해지는 것을 직접 확인할 수 있는 곳은 하늘입니다. 오로라를 절대 볼 수 없었던 적도지방뿐만 아니라 지구 곳곳에서 오로라가 나타날 수 있습니다. 자기권의 보호 속에서 지구의 생태계는 지금까지 진화할 수 있었습니다. 자기권이 없어진다면 생명은 모두 사라지고 지구는 죽은 땅이 될 것입니다. 사실 지구자기장은 45억년 전 생성된 이래 수천 번 뒤집어졌습니다. 그러나 인류는 아직 이를 겪지 못했습니다. 지구자기장의 역전은 모든 생명에게 큰 영향을 미칠 것입니다. 과거의 자기 역전과 대멸종의 관계는 아직도 과학계의 숙제로 남아 있습니다. 우리에게는 적응만이 살 길입니다.

Forget global warming, worry about the MAGNETOSPHERE: Earth's magnetic field is collapsing and it could affect the climate and wipe out power grids

• Earth's magnetic field has weakened by 15 per cent over the last 200 years
• Could be a sign that the planet's north and south poles are about to flip
  
• If this happens, solar winds could punch holes into the Earth's ozone layer
  
• This could damage power grids, affect weather and increase cancer rates
• Evidence of flip happening in the past has been uncovered in pottery
  
• As the magnetic shield weakens, the spectacle of an aurora would be visible every night all over the Earth

By ELLIE ZOLFAGHARIFARD

PUBLISHED: 12:38 GMT, 27 January 2014 | UPDATED: 17:25 GMT, 31 January 2014

 
 
 

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Deep within the Earth, a fierce molten core is generating a magnetic field capable of defending our planet against devastating solar winds.

The protective field extends thousands of miles into space and its magnetism affects everything from global communication to animal migration and weather patterns.

But this magnetic field, so important to life on Earth, has weakened by 15 per cent over the last 200 years. And this, scientists claim, could be a sign that the Earth’s poles are about to flip. 

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The Earth's protective field extends thousands of miles into space and its magnetism affects everything from global communication to animal migration and weather patterns

Experts believe we're currently overdue a flip, but they're unsure when this could occur. 

If a switch happens, we would be exposed to solar winds capable of punching holes into the ozone layer. 

The impact could be devastating for mankind, knocking out power grids, radically changing Earth’s climate and driving up rates of cancer.

‘This is serious business’, Richard Holme, Professor of Earth, Ocean and Ecological Sciences at Liverpool University told MailOnline. ‘Imagine for a moment your electrical power supply was knocked out for a few months †瘀攀爀y little works without electricity these days.’

 

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The Earth's climate would change drastically. In fact, a recent Danish study believes global warming is directly related to the magnetic field rather than CO2 emissions.

The study claimed that the planet is experiencing a natural period of low cloud cover due to fewer cosmic rays entering the atmosphere.

Radiation at ground level would also increase, with some estimates suggesting overall exposure to cosmic radiation would double causing more deaths from cancer.

Researchers predict that in the event of a flip, every year a hundred thousand people would die from the increased levels of space radiation.

'Radiation could be 3-5 times greater than that from the man-made ozone holes. Furthermore, the ozone holes would be larger and longer-lived,' said Dr Colin Forsyth from the Mullard Space Science Laboratory at UCL.

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The magnetosphere is a large area around the Earth produced by the planet's magnetic field. It presence means that charged particles of the solar wind are unable to cross the magnetic field lines and are deflected around the Earth

The magnetosphere is a large area around the Earth produced by the planet’s magnetic field. It presence means that charged particles of the solar wind are unable to cross the magnetic field lines and are deflected around the Earth.

Space agencies are now taking the threat seriously. In November, three spacecraft were launched as part of the SWARM mission to uncover how the Earth’s magnetic field is changing.

The mission plans to provide better maps of our planet's magnetic field and help scientists understand the impact of space weather on satellite communication and GPS.

‘Whilst we have a basic understanding of the interior of the Earth, there is much we still don’t know,’ said Dr Forsyth.

‘We do not fully understand how the Earth’s magnetic field is generated, why it is variable and the timescales of these variations.’

The mission will provide a current map of Earth’s magnetic field. But historic evidence of its decline has already been found in a surprising source †ancient pottery.

Scientists have discovered that ancient pots can act as a magnetic time capsule. This is because they contain an iron-based mineral called magnetite. When pots form, the magnetite minerals align with the Earth’s magnetic field, just like compass needles.

WHAT IS GEOMAGNETIC REVERSAL?

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The Earth’s magnetic field is in a permanent state of change. Magnetic north drifts around and every few hundred thousand years the polarity flips so a compass would point south instead of north. The strength of the magnetic field also constantly changes and currently it is showing signs of significant weakening.

The Earth magnetic field is mainly generated in the very hot molten core of the planet. The magnetic field is basically a dipole (it has a North and a South Pole). Magnetic reversal or flip is the process by which the North Pole is transformed into the South and vice versa, typically following a considerable reduction in the strength of the magnetic field. However, weakening of the magnetic field does not always result in a reversal.

During a reversal, scientists expect to see more complicated field pattern at the Earth's surface, with perhaps more than one North and South Pole at any given time. The overall strength of the field, anywhere on the Earth, may be no more than a tenth of its strength now.

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The Earth's magnetic field is generated in the very hot molten core of the planet. Scientists believe Mars used to have a magnetic field similar to that on Earth which protected its atmosphere

By examining pottery from prehistory to modern times, scientists have discovered just how dramatically the field has changed in the last few centuries.

They’ve found that Earth’s magnetic field is in a permanent state of flux. Magnetic north drifts and every few hundred thousand years the polarity flips so a compass would point south instead of north.

If the magnetic field continues to decline, over billions of years, Earth could end up like Mars - a once oceanic world that has become a dry, barren planet incapable of supporting life.

WHAT ARE THE DANGERS OF A MAGNETIC FLIP?

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Life has existed on the Earth for billions of years, during which there have been many reversals. 

There is no obvious correlation between animal extinctions and those reversals. Likewise, reversal patterns do not have any correlation with human development and evolution. 

It appears that some animals, such as whales and some birds use Earth's magnetic field for migration and direction finding. 

Since geomagnetic reversal takes a number of thousands of years, they could well adapt to the changing magnetic environment or develop different methods of navigation.

Radiation at ground level would increase, however, with some estimates suggesting that overall exposure to cosmic radiation would double causing more deaths from cancer. ‘But only slightly,’ said Professor Richard Holme. 

‘And much less than lying on the beach in Florida for a day. So if it happened, the protection method would probably be to wear a big floppy hat.’

Electric grid collapse from severe solar storms is a major risk. As the magnetic field continues to weaken, scientists are highlighting the importance off-the grid energy systems using renewable energy sources to protect the Earth against a black out. 

'The very highly charged particles can have a deleterious effect on the satellites and astronauts,' added Dr Mona Kessel, a Magnetosphere discipline scientist at Nasa. 

In one area, there is evidence that a flip is already occurring. ‘The increasing strength of the South Atlantic anomaly, an area of weak field over Brazil, is already a problem,’ said Professor Richard Holme. 

The Earth's climate could also change. A recent Danish study has found that the earth's weather has been significantly affected by the planet's magnetic field.

They claimed that fluctuations in the number of cosmic rays hitting the atmosphere directly alter the amount of cloud covering the planet.

Henrik Svensmark, a weather scientist at the Danish National Space Centre who led the team behind the research, believes that the planet is experiencing a natural period of low cloud cover due to fewer cosmic rays entering the atmosphere.

But scientists claim the rate of decline is too fast for the Earth’s core to simply burn out. Instead, the story told by ancient pottery suggests the Earth's poles could be about to undergo another flip.

According to the British Geological Survey, the Earth's magnetic field has on average four or five reversals in polarity every million years and we’re now overdue a similar event.

‘At the moment, we cannot accurately determine whether or not the Earth’s field is about to flip,’ said Dr Forsyth. ‘We have only been recording the Earth’s field for around 170 years; about 1-15 per cent of the time a flip is expected to take.’

If a flip occurs, it would cause the Earth’s magnetic shield to be weakened for thousands of years, opening up our defences and causing cosmic radiation to get through.  

'We have a double layer defence shield,' said Jim Wild a space scientists at Lancaster University. 

'Space is full of stuff that’s not great for biological tissue. If we didn’t have an atmosphere, that stuff would be hitting us. It’s the magnetic field protects atmosphere from the solar wind.'

 

‘Some speculative studies have suggested that as the Earth’s magnetic field weakens we could see an increase in cloud coverage in the troposphere and an increase in the polar ozone holes,’ added Dr Forsyth.

‘This would be particularly evident in the northern hemisphere where up to 40 per cent of the ozone within the hole region could be lost, far greater than the current losses.’

In fact, in one area, there is evidence that a flip is already occurring. ‘The increasing strength of the South Atlantic anomaly, an area of weak field over Brazil, is already a problem,’ said Professor Holme. 

Mapping the magnetic field: Why it matters

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Not all of the effects of a weak magnetic field will be bad. The much sought-after spectacle of an aurora would be visible every night all over the Earth as solar winds hit the atmosphere

‘Satellites flying over have far more problems than in other locations. Astrophysical satellite are just switched off in this location, but from my perspective, this isn’t much good if you want to study the Brazilian rainforest.’

'The very highly charged particles can have a deleterious effect on the satellites and astronauts,' added Dr Mona Kessel, a Magnetosphere discipline scientist at Nasa. 

Scientists however, are quick to point out that while a magnetic flip could cause problems for mankind, the event won’t be a catastrophic.

‘We’ve had many reversals in the past, and haven’t been able to show that they had anything to do with, for example, mass extinctions,’ said Professor Holme.

And not all of the effects will be bad. The much sought-after spectacle of an aurora would be visible every night all over the Earth as solar winds hit the atmosphere.

There remains, however, much work yet to be done in understanding the properties of the deep Earth.

The Earth’s core is a hostile world where the crushing forces and temperatures, similar to that of the surface of the sun, take our scientific understanding and abilities to the limit.

'This isn't some crazy theory that might happen,' said Professor Wild. 'There is evidence, but we still need to do more science to understand the impact...I'm confident we can come up with a solution.'

WHAT IS THE SWARM MISSION?

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Swarm is a ESA satellite mission which was launched on 22nd November 2013.

The mission consists of three identical satellites which will precisely measure the strength and direction of Earth's magnetic field. The new data will be processed by British Geological Survey to produce an accurate map of this field.

In order to best measure the field, the satellites will orbit in a unique configuration. Two satellites will fly side-by-side at height of 450 km, while the third satellite will fly at an altitude of 530 km. 

The lower two satellites will allow very fine measurements of the magnetic field generated by the rocks in the Earth's crust, which are difficult to detect otherwise. The upper satellite will give a simultaneous measurement at a different location.

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