Van Allen Probes Reveal an Impenetrable Barrier in Space

December 1, 2014


Using NASA’s Van Allen Probes, new research reveals that the Van Allen radiation belts contain a nearly impenetrable barrier that prevents the fastest, most energetic electrons from reaching Earth.

This movie shows how particles move through Earth’s radiation belts, the large donuts around Earth. The sphere in the middle shows a cloud of colder material called the plasmasphere. New research shows that the plasmasphere helps keep fast electrons from the radiation belts away from Earth. Image Credit: NASA/Goddard/Scientific Visualization Studio

The Van Allen belts are a collection of charged particles, gathered in place by Earth’s magnetic field. They can wax and wane in response to incoming energy from the sun, sometimes swelling up enough to expose satellites in low-Earth orbit to damaging radiation. The discovery of the drain that acts as a barrier within the belts was made using NASA’s Van Allen Probes, launched in August 2012 to study the region. A paper on these results appeared in the November 27, 2014, issue of Nature magazine.

“This barrier for the ultra-fast electrons is a remarkable feature of the belts,” said Dan Baker, a space scientist at the University of Colorado in Boulder and first author of the paper. “We’re able to study it for the first time, because we never had such accurate measurements of these high-energy electrons before.”

Understanding what gives the radiation belts their shape and what can affect the way they swell or shrink helps scientists predict the onset of those changes. Such predictions can help scientists protect satellites in the area from the radiation.

The Van Allen belts were the first discovery of the space age, measured with the launch of a US satellite, Explorer 1, in 1958. In the decades since, scientists have learned that the size of the two belts can change – or merge, or even separate into three belts occasionally. But generally the inner belt stretches from 400 to 6,000 miles above Earth’s surface and the outer belt stretches from 8,400 to 36,000 miles above Earth’s surface.

A slot of fairly empty space typically separates the belts. But, what keeps them separate? Why is there a region in between the belts with no electrons?

Enter the newly discovered barrier. The Van Allen Probes data show that the inner edge of the outer belt is, in fact, highly pronounced. For the fastest, highest-energy electrons, this edge is a sharp boundary that, under normal circumstances, the electrons simply cannot penetrate.

NASA Spots an Impenetrable Barrier in Space

A cloud of cold, charged gas around Earth, called the plasmasphere and seen here in purple, interacts with the particles in Earth’s radiation belts — shown in grey— to create an impenetrable barrier that blocks the fastest electrons from moving in closer to our planet. Image Credit: NASA/Goddard

“When you look at really energetic electrons, they can only come to within a certain distance from Earth,” said Shri Kanekal, the deputy mission scientist for the Van Allen Probes at NASA’s Goddard Space Flight Center in Greenbelt, Maryland and a co-author on the Nature paper. “This is completely new. We certainly didn’t expect that.”

The team looked at possible causes. They determined that human-generated transmissions were not the cause of the barrier. They also looked at physical causes. Could the very shape of the magnetic field surrounding Earth cause the boundary? Scientists studied but eliminated that possibility. What about the presence of other space particles? This appears to be a more likely cause.

The radiation belts are not the only particle structures surrounding Earth. A giant cloud of relatively cool, charged particles called the plasmasphere fills the outermost region of Earth’s atmosphere, beginning at about 600 miles up and extending partially into the outer Van Allen belt. The particles at the outer boundary of the plasmasphere cause particles in the outer radiation belt to scatter, removing them from the belt.

This scattering effect is fairly weak and might not be enough to keep the electrons at the boundary in place, except for a quirk of geometry: The radiation belt electrons move incredibly quickly, but not toward Earth. Instead, they move in giant loops around Earth. The Van Allen Probes data show that in the direction toward Earth, the most energetic electrons have very little motion at all – just a gentle, slow drift that occurs over the course of months. This is a movement so slow and weak that it can be rebuffed by the scattering caused by the plasmasphere.

This also helps explain why – under extreme conditions, when an especially strong solar wind or a giant solar eruption such as a coronal mass ejection sends clouds of material into near-Earth space – the electrons from the outer belt can be pushed into the usually-empty slot region between the belts.

“The scattering due to the plasmapause is strong enough to create a wall at the inner edge of the outer Van Allen Belt,” said Baker. “But a strong solar wind event causes the plasmasphere boundary to move inward.”

A massive inflow of matter from the sun can erode the outer plasmasphere, moving its boundaries inward and allowing electrons from the radiation belts the room to move further inward too.

The Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, built and operates the Van Allen Probes for NASA’s Science Mission Directorate. The mission is the second in NASA’s Living With a Star program, managed by Goddard.

Publication: D. N. Baker, et al., “An impenetrable barrier to ultrarelativistic electrons in the Van Allen radiation belts,” Nature 515, 531–534 (27 November 2014); doi:10.1038/nature13956

Source: Karen C. Fox, NASA’s Goddard Space Flight Center

Images: NASA/Goddard

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47 Responses to “Van Allen Probes Reveal an Impenetrable Barrier in Space”

  1. Brutus Says:

    Uh… was it again we made it to the moon without being fried>?


    • Jflyer Says:

      Precisely. Amazing how the media never questions that sacred cow.


    • TattiePie Says:

      You exit through the areas that are weaker, simple as that.


    • Carl Says:

      With very good shielding and a limited exposure. If a large CME had occurred and they had flown through it, who knows what would have happened. Would the shielding on their ship have been suffient? I am not sure, but we might have ended up with fried astronauts. I’m glad nothing like that ever happened.


    • mark scheuer Says:

      The astronauts were safe because they were enclosed in a metal spacecraft. Being a conductor, the metal allowed the electrons to arrange themselves on the sureface so that the electric field inside the craft was nullified. This is a direct consequence of the inverse square law of the electric force.


      • ian brown Says:

        Perhaps you should contact NASA and inform them that you figured out how to get through the radiation belts, because they still haven’t figured it out..


        • Kmrod Says:

          Yes, they have figured out how to get through the van Allen belts. The people who say the NASA engineer slipped and revealed that “we still haven’t figured out” need a remedial grammar class.


    • CR Says:

      They were in the Van Allen belt for too short a time to affect them.


    • Wake Says:

      If you wish to be fried you can always colonize Mars.


    • Slim Says:

      I’ve wondered about this for a while now.


    • John Says:

      But even with Starfish Prime, additional research into the Van Allen belts determined they weren’t a deal breaker for missions to the Moon. (By 1969, the high-energy electrons injected into the lower Van Allen belt by the Starfish Prime event had decayed to one-twelfth of its post-test peak intensity.) By February of 1964, NASA was confident that Apollo crews would be passing through the belts fast enough that the spacecraft’s skin and all the instrumentation lining the walls would be enough protection. It might seem foolhardy in hindsight for NASA to have accepted the risks of send astronauts through the Van Allen belts without extra protection, but it was a minor risk in the scheme of the mission.


    • Neil Says:

      We grew to be bigger than electrons and took some mylar shielding with us


    • duh Says:

      Didn’t happen.
      We have not been to the moon.


    • JeffM Says:

      Uh…It’s called physics…Something you don’t understand based on your comment.


    • Patrick Says:

      Well Brutus, our getting to the moon and back several times must prove that WE are not the fastest, high energy, relativistic ultra electrons that the Van Allen Belts repels. And as your 3rd grade teacher told you, read ALL your homework before asking Questions about it.


    • Bill Nada Says:

      Impenetrable to electrons, not human spacecraft.


    • Jim Holland Says:

      The length of time astronauts were exposed was not a lethal dose.

      You would be fried if left there for years.

      Idiots. Faking a lunar landing would be impossible due the the number of people required to keep the secret.


    • eddy Says:

      Bet you believe in intelligent design too you moron.


      • Rick Says:

        Re Intelligent design: It’s easier to believe the Mona Lisa painting happened by an explosion in an art studio than believing the 40 components of a virus’ tail propulsion motor happened by chance.


  2. Nik Says:

    Now remember! Such amazing feats such as this to protect us are all by chance…or so we’re told.


    • Alli Bugger Says:

      This is all something that Obama started when he was still a senator.


    • Raji Says:

      Quit acting like a moron!


    • Dale Says:

      Yes ,Isn’t it amazing how the so called geniuses are still not getting it that a bang just doesn’t put up all this protection and everything else that is in the world. I am amazed the ,,,,, no I am not going there. We know and if they do not want to hear it may be the best way to teach them is say BYBy we won’t see you again.


    • Van Says:

      Nik,this is just more evidence that we are living in a vast computer simulation. God wouldn’t need to hide from us! But a couple programmers would! Just go online and search “Computer Universe Simulation,” and sees what comes up!


  3. Billy Bob Says:

    “the most energetic electrons have very little motion at all – just a gentle, slow drift that occurs over the course of months.”…eh?

    I think by definition, the most energetic electrons will be moving incredibly fast. That’s sort of what “energetic” electrons means. Unless we are talking about excited electrons bound to nuclie, but we aren’t because this is plasma.

    Sorry, I quit reading after the author demonstrated his lack of understanding.


  4. Wake Says:

    I hate to point this out but it’s been known almost since Van Allen charted these belts circa 1958. Each succeeding space exploration trip has shown that these belts contain protons as energetic as 100 MeV and that little to no electrons emitted from the Sun could penetrate that envelope.


  5. JonaD Says:

    The word ‘impenetrable’ does NOT apply to humans or our spacecraft… and frankly it is only applicable to certain charged particles with certain energies traveling at particular vectors.

    But apparently, the term ‘impenetrable barrier’ was necessary to attract the attentions of even a tiny segment of our plebeian masses… to most people, ‘physics’ is merely a tabloid fascination, not anything to take seriously.

    I think in the name of popularizing physics, the authors should have called the onion-like layers of the belts… ‘Phasors’, so that people would learn to fear them.


  6. Jenius Says:

    The “barrier” is obviously the distances involved.


  7. SteveO Says:

    Wonder if the particles are negative the earths magnetic field cuasing them to be repelled, but at the same time gravity from the earch keeps them where they are. As these two forces fluctuate so does the thickness/distance of the particles from earch.


  8. MARCIAL Says:



    • Patrick Says:

      And more reasons why some people believe the Earth is flat Marcial.
      Thinking is hard and makes their head hurt


  9. John Says:

    Maybe it does not effect us as much as we think it does.. I don’t know if we knew of such things back in the day.. but that is most likely what is stopping us now a days is because we learned new things about how dangerous space can be and with all the space junk in our Orbit.. kinda makes things a little harder


  10. Bill Says:

    It doesn’t stop gamma rays.


  11. maj Says:

    So more proof that the moon landing was a fucking scam!


  12. Chuck Says:

    Wow! This is valuable information that can help prevent communication loss that may result in millions to billions of lost dollars and productivity. Another example of how well government works for the people.


  13. Ted Says:

    This is precisely why the Russians abandoned their quest for the moon.


  14. MEE Says:

    I thought K already established that in M.I.B.


  15. Tom Says:

    Plebeian masses? WTF?


  16. Chaz Says:

    Yeah the moon landings were fake as are all the smart phones and other technologies we pretend to use. come on peeps


  17. lalala Says:

    then, how’s that we have so many satellites flying out of the solar system, or near mars, mercury, even the sun, without getting fried by the radiation because they are far out the protection of the belt? always wandered that.


  18. Jean Says:

    please someone help me did apollo 11 had a combustion engine?


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