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A Natural Particle Accelerator, Far Above The Planet


Far above the Earth's surface, two doughnuts of radiation surround the planet, charged particles zipping around in stable belts - that's the shape of them - and they were discovered in 1958 by James Van Allen and now bear his name. They are the Van Allen Belts.

But when researchers launched a satellite in 2012 to study them, just a few days after the satellite was brought online, scientists were treated to surprise: a third belt, which then joined the other two known belts but joined them only for about a month before that third belt was blown away, a puff - by a strong puff of solar wind, strange stuff, and showing just how little we know about our space environment.

It was really interesting research, and joining me now is Daniel Baker. He is director of the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder and one of the authors of a paper in Science describing the phenomena. Welcome to SCIENCE FRIDAY.

DANIEL BAKER: Thank you very much for having me.

FLATOW: Surprising, was it?

BAKER: Very much, yes. As you noted, since their discovery over five decades ago, the textbooks told us there were two distinct Van Allen radiation belts. We always believed there was a stable inner zone and a highly dynamic outer zone separated by each other.

FLATOW: I remember learning - I remember one of my projects in seventh grade was studying an article, when I guess it was either Sputnik was up there, or Explorer, and they discovered the Van Allen Belts, and it was cutting a piece of - an article out of the New York Times and put it in a scrap book, but it was - that dates all the way back to that.

BAKER: That's right, yeah. The discovery was really made by Van Allen and co-workers with the Explorer 1 and then the Explorer 3, 4 and Pioneer missions in that time period of 1958 or so.

FLATOW: And how do you discover a belt with a satellite?

BAKER: Well, you really use very highly sensitive particle detection devices. You put them onto satellites. You fly the satellites through there. You make in situ observations, and you try to sort it all out. And that's what we did with the - you mentioned one satellite. It was actually two satellites, the dual satellite mission called the Radiation Belt Storm Probes, and they've now been renamed the Van Allen Probes Mission.

FLATOW: And so what do you actually see?

BAKER: What we saw was that when we first turned on our experiment about two days after launch, we saw the expected two-belt structure. We saw high intensity near the Earth, then a gap region, and then an outer belt. But just a short while after that, part of that outer dynamic belt was ripped away, and it left what we've called the Storage Ring for about four weeks, I think as you noted in your introductory remarks.

And we were so surprised by this. We thought our instruments must be wrong. But then we realized we build such good instruments that couldn't possibly be true. And we saw the same thing on both satellites. So we really thought this must be for real.

And then as you noted, about four weeks after that, a powerful solar storm came by and wiped out the entire outer Van Allen Belt for a while. So this is really quite exciting stuff. The sun really cooperated very actively for about a month and a half or two months.

FLATOW: So does that mean this is an area or a belt that comes and goes all the time?

BAKER: Well, we don't really know that. I would be very surprised in the last four and a half billion years if this hasn't happened before. But we've never really had the eyes in space to see this. We have better energy range, better time resolution, better spatial resolution, better energy resolution, than we've ever had before.

And as I say, to have two satellites that allow us to separate space and time is also very advantageous. So we're keeping our eyes open. We certainly haven't seen this in the five months since the launch except for this period of time that I report in the paper.

FLATOW: Yeah, so you're convinced, though, that it's not some artifact?

BAKER: Oh yes, we're very much convinced. In fact separate instruments - with 20/20 hindsight we've been able to go back and look at this in other instruments on the same spacecraft that we're on sort of sporadically. And we've seen hints from other satellites. But it was never seen as clearly as this, as we can see now, flying through the throat of the Van Allen Accelerator.

FLATOW: 1-800-989-8255 is our number, we're talking with Daniel Baker, director of the Laboratory for Atmospheric and Space Physics, University of Colorado in Boulder. You can also tweet us, @scifri. So you have no idea why, then, this happened?

BAKER: Well, we sort of think that - we're getting ideas, and theoreticians, of course, are very excited by these kinds of results and are now coming out with many ideas. But it seems like it was, sort of, a Goldilocks scenario, in a way. There was a strong acceleration event. Part of the outer belt got ripped away by a solar disturbance that was just strong enough to tear away part of the outer belt, but not strong enough to completely annihilate the outer belt.

And then it was book-ended about the 30th of September, a much more powerful solar disturbance came by and really annihilated the entire outer belt. So it seems like it has to be a sequence, a special sequence of events in order for this to really occur and to be detectable for such a long period of time.

FLATOW: Was this - was there any bit of serendipity on this, that you were able to detect it?

BAKER: There absolutely was. That's a fascinating part of the story. We learned early in the summer of 2012 that a longstanding monitoring satellite called SAMPEX, the Solar Anomalous Magneto Particle Explorer, that had been sort of remotely sensing the radiation belt. So it was going to re-enter the Earth's atmosphere some time in the fall of 2012. So we went on a campaign to try to get our instruments commissioned much earlier. If we had followed the normal pattern of commissioning our relativistic electron proton telescope would have not been turned on until about 34 days after launch.

We pushed to turn on two days after launch, and it was precisely because of that that we were able to detect these things, see them and watch them in their full kind of glory for this entire period of time. If we hadn't had SAMPEX forcing our hand, we would have not turned on until after this was all over and we would have missed the very interesting story, to say the least.

FLATOW: That is - it seems that you got really lucky...


FLATOW: ...what other way to describe it.

BAKER: That's right.

FLATOW: How could the early explorers have detected the belt if you're using sophisticated satellites 50 years later? What were they doing that they could detect it?

BAKER: Well, they...

FLATOW: What did Van Allen do?

BAKER: Well, he was using pretty simple instrumentation, what are called Geiger tubes. You probably heard of Geiger counters that make very sort of broad-brush, fairly crude kind of measurements of radiation. They don't distinguish very clearly between different energies or different particles even. And today, we have much, much improved technology, very sophisticated instruments that can see with better spatial resolution, better temporal resolution and especially better energy resolution extending up to the very highest energies.

And so modern technology combined with flying spacecraft sort of in the right place and, of course, at the right time really helps us to do a far superior job to anything that's been done before.

FLATOW: Are you going to name this belt something?

BAKER: Well, as they say, we called it the storage ring. I was sort of motivated by looking at what's going on in ground-based laboratories, you know, ground accelerators and things like that. I don't know that we will do anything but maybe call it a third or a transient belt, but we'll have to see. We might have a naming contest or something.

FLATOW: Oh, we have one that came in already.

BAKER: Oh, what's that?

FLATOW: A tweet came in to us saying, you know, you made your discovery in the same week that Van Cliburn died, you know, the great pianist, maybe the Van Cliburn belt, since you have the Van Allen belt.


BAKER: Well, we'll take that under advisement, OK?


FLATOW: All right. 1-800-989-8255. Let's talk about why it's so important. Why do you spend the time, money and effort to send up these satellites to study the belts? Why is that so important?

BAKER: Well, the radiation in space is very important. All the satellites that we use in our sort of everyday life or that society uses for communication, for surveillance, for weather satellites, all the things that we take for granted today involving the space segment really involves satellites that fly through these regions. And so the more we understand about the space environment and especially understanding when the space environment is particularly hostile is very important.

We know many, many cases where satellites have suffered severe anomalies or even failures due to these Van Allen radiation belt particles. And so we're trying to understand this. And so we're very fortunate to be part of a discipline that has both fundamental astrophysical kind of benefits, you know, basic research benefit to understand this cosmic accelerator operating just a few thousand miles above our head, but we also have the duality there of studying things that have real societal relevance. And that's why it's kind of a fun discipline to be part of.

FLATOW: This is Ira Flatow on SCIENCE FRIDAY from NPR, talking with Dan Baker, University of Colorado in Boulder. Do these belts protect us from that radiation that's coming from the sun?

BAKER: Well, the magnetic field around the Earth very much protects us. We're under two very important umbrellas. One is the magnetic field of the Earth that sort of stands off the direct impact of solar energetic particles and the flow of the solar wind, and then the atmosphere also shields us. So when we're out in space, whether it's robotic spacecraft or humans flying out there that they can be pretty directly impacted by these high-energy charged particles. But we here on Earth are relatively protected, and we live in a very protective cocoon in a way.

FLATOW: Let's go to Dan in Fort Lauderdale. Hi, Dan. Welcome to SCIENCE FRIDAY.

DAN: Hi. How are you doing?

FLATOW: Hey there.

DAN: Thanks for taking my call. I just have a real quick question. I want to understand the shape of these, because when I think of the word belt, I think of like an asteroid belt, like, you know, the solar system-type track, you know? And so I was wondering if it's around the Earth and if it's like a sphere shape, like completely closed.

FLATOW: Good question.

BAKER: Yeah. It is a very good question. Actually, these are more like sort of doughnuts. I think Ira used that term before, or they're sort of like Tauruses around the Earth. And so belts suggest something quite thin and narrow, and these are really quite broad. They're like the Earth is enveloped in a couple of interlaced kind of inner tubes or something like that. It's much more Taurus-like rather than belt-like. It's just that name belt is a holdover from the earliest discoveries.

FLATOW: Yeah. Let's go to Mickey(ph) in Tampa. Hi, Mickey. Welcome to SCIENCE FRIDAY.

MICKEY: Hi, Ira.

FLATOW: Hi there.

MICKEY: My question is it's regarding the two inner belts. What are their characteristics? What - why is it that they were less affected by the solar wind kind of puffing away this third belt?

FLATOW: Yeah. Good question.

BAKER: Yeah. That's a very good question too. And the outermost part of the system is really buffeted very strongly by the solar wind. As you get closer to the Earth, the magnetic field becomes much stronger. It's much more immune there to the external perturbations from the sun. And so the inner belt is very stable, very tightly held by the strong magnetic field, whereas the outermost fringes of the system can be buffeted very strongly by the solar wind flow.

FLATOW: Would you be more surprised now if you don't see another belt develop or if you do?

BAKER: I would be surprised. Now, that we have the clear eyes, the clear windows on this phenomenon, I'd be amazed if we don't see it, you know, again under the right circumstances. But what we don't know is how frequently these circumstances occur. And it probably takes the sun to cooperate, and we haven't been too fortunate lately to get the sun to do just what we want it to do.

FLATOW: Well, now that we're talking about it, of course, it will never happen again.


BAKER: Well, we hope we won't have the kiss of death for that.

FLATOW: All right. Dr. Baker, thank you very much for...

BAKER: Thank you.

FLATOW: ...taking time to be with us.

BAKER: Nice talking. Thanks. Bye.

FLATOW: You're welcome. Daniel Baker, director of the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. When we come back, something completely different. When nerds become rappers, what does it sound like? The music of Nerdcore. Yeah, nerds can become rappers too. And we'll be right back and let you listen in. We have a special guest. So stay with us. We'll be right back after this break.


FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY, from NPR. Transcript provided by NPR, Copyright NPR.