Space

Raise shields: Protective invisible barrier found surrounding Earth

Raise shields: Protective invi...
A natural shield has been found to protect the Earth from "killer electrons"
A natural shield has been found to protect the Earth from "killer electrons"
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One of the Van Allen probes (Image: NASA)
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One of the Van Allen probes (Image: NASA)
A natural shield has been found to protect the Earth from "killer electrons"
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A natural shield has been found to protect the Earth from "killer electrons"
Diagram of the plasmasphere and radiation belts (Image: NASA/Goddard)
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Diagram of the plasmasphere and radiation belts (Image: NASA/Goddard)
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The idea of putting a Star Trek-like force field around the entire Earth seems like the fodder for a fairly silly science fiction epic out of the 1930s, but according to space scientists, such a barrier already exists. Discovered by a pair of NASA space probes, the natural shield protects the Earth and near-Earth satellites from so-called "killer electrons" with a precision that cuts it off like a wall of glass.

The barrier was found within the Van Allen Belts, which are two distinct zones of radiation that are shaped like a pair of distended donuts that grow, shrink, shift, and even split or merge under the impact of radiation from the Sun. Formed by charged particles captured by the Earth's magnetic field, they were discovered by America's first space probe, Explorer I in 1958. The inner belt spans from 400 to 6,000 mi (650 to 9,500 km) above the Earth and the outer belt is between 7,200 and 36,000 mi (12,00 to 58,000 km).

Diagram of the plasmasphere and radiation belts (Image: NASA/Goddard)
Diagram of the plasmasphere and radiation belts (Image: NASA/Goddard)

The belts are of more than academic importance. The radiation from the particles are a serious hazard to satellites and astronauts, and scientists pay close attention to the belts' activity because a sudden expansion could end up damaging satellites in low Earth orbit and even pose a hazard to manned space missions.

The most dangerous of these charged particles are the ultrafast, ultrarelativistic, or "killer" electrons. These are moving so fast that they pack a massive punch and damage electronic circuits and living tissue.

The curious thing is, the belts are better behaved than originally thought. Instead of drifting down toward Earth's atmosphere, the inner edge of the outer belt has a very sharp edge at 7,200 mi from Earth, leaving a space between the inner and outer belts, and in this this gap there are no ultrafast electrons. This cutoff is so pronounced that scientists studying it compare it to a glass wall that the electrons can't penetrate.

The barrier was discovered using 20 months of data from NASA's pair of Van Allen probes, which were launched in August 2012 and, as the name suggests, work in tandem to study the belts.

One of the Van Allen probes (Image: NASA)
One of the Van Allen probes (Image: NASA)

A team of scientists led by the University of Colorado Boulder looked through the Van Allen probes' data in hopes of finding the cause of the barrier. After eliminating human activity, such as radio transmissions, and the Earth's magnetic field, they found the most likely candidate in the form of the plasmasphere, which is a cloud of cool charged particles that extends from the upper regions of the Earth's atmosphere from 600 mi (965 km) up to near the edge of the outer Van Allen belt.

According to the team, the ultrafast electrons interact with the plasmasphere and are repelled. Although the electrons' energy is so high that they could easily penetrate the cloud, the electrons instead move around the Earth in huge circles at 100,000 mps (160,000 km/s), grazing the plasmasphere. The allows the plasmasphere to nudge the electrons away in much the same manner as a relatively flimsy traffic barrier deflecting a speeding car back onto the road when the car could have crashed through the barrier if it had hit it dead on. This interaction is called the plasmaspheric “hiss,” because it makes a sound over radio receivers that can be compared to static.

Another piece of evidence for the barrier is when it fails under extreme conditions, such as a massive solar flare, which can erode the plasmasphere and push the electrons through and into the gap. However, such a breach would only last a short time, which scientists say demonstrates the strength of the "hard, fast" barrier.

The team's results were published in the journal Nature.

Sources: University of Colorado Boulder, NASA

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10 comments
Steven Evers
Finding another life friendly planet like earth to live on just got infinitesimally smaller...
ETorNotET
@Steven May be not... if one have a faith in the theory of evolution. Since intelligent life can evolve from rock and dirt, why would it be limited to this planet alone one would argue? This finding is proof that this third Rock from the sun had not only spawned life as we know it, but had evolved itself from inert rock into an intelligent habitat which include this defensive mechanism among untold number of systematically complex and intricate correlations that sustain all living things.
In any case, this earth is a pretty interesting study of seemingly endless complex designs in my opinion. And the hard question for many people is : was the earth designed intelligently or evolved intelligently?
Ryan Gibbons
Not really there still is a good chance.. Actually I think that a earth sized rocky planet, in the Goldilocks zone, with a molten core is most likely to have a strong enough magnetic field.
This is coming from a creationist religious person. Open your mind.
There are other habitable planets, with at least basic life, out there. It is not a question of whether they exist, its a question of when we will discover one; if its statistically and scientifically possible to find one with current knowledge and technology.
Michiel Mitchell
I can assure you, my luck dictates that the chance of me landing on the only planet in existence with all the right ingredients for me to be able to breath on it... is in order of magnitude 1000000 times smaller than 1 over 10 to the power of the speed of light multiplied by the radius of the sun*2. Which leaves me with only one conclusion.... there are literally trillions upon trillions of these planets all over the place...
pychap
Ah! Fascinating. Now they'll find a new way that Global Warming damages and will destroy the fields!
StWils
There is no apparent reason that the charged particle belt around Earth is somehow unique to Earth. Just because we have only recently gotten around to observing it does not mean similar conditions do not exist elsewhere.
Daniel Gregory
It is great to know that the planet has mechanisms to protect itself from the sun, and thus protecting the life which inhabits it. Perhaps the Earth itself is a super organism.
Walt Stawicki
@Ryan Gibbons it aint just "molten core"! its ferro magnetic molten core! as a high trans ferrous metals (gold and platinoids from nova events are rare even on other physically well placed dirtballs) glob, we are very fortunate. To say any glob so placed will do is to ignore part of what well placed, well provisioned well suited... really entails.
@ ETorNotET "in the beginning was the logos ( we say word in the west). The taoists are not so anthrpocentric. Nor do they bother in speculation of that which is beyond comprehension (and prefer to not even give a name). They concern themselves with the visible and the puny "secrets" that such observation might reveal. logos, order, the divine order of the elements, from atoms to living, emergent ( inevitable, even, within a near infinite set of experiments- universe) properties, like us and mind. To we taoists, jeffersonian diests, thats enough to keep us humble and in our place!
@ pychap wow! and OMG!
@ yeah..."could be" BUT see above (others and my) and think! could be! grumphhh!
Oskar Andersson
So no one else thought Arc Net Shield from MIB?
Ralf Biernacki
Philosophical and theological musings aside, both the pictures illustrating the article are wrong. The barrier is not a shield somewhere between the radiation belts, much less cutting through them. It constitutes the inner surface of the outer Van Allen belt.
Are there "ultrafast" electrons in the inner belt? Or is it based around different particles? Does it have an inner barrier of its own?
Is there an outer barrier as well, to either Van Allen belt? If there is, that would pretty much account for the belts existence in the first place--the particles making up the radiation are confined between the two barriers.
If the main contributor to V-E belt radiation is the herd of fast electrons, would that mean that the infamous radiation belts are mostly beta radiation? If so, this is good news, as beta radiation is much easier to shield against than gamma. But I doubt they only found that out now.