Mapping The Boundaries Of The Solar System

NASA launched the Interstellar Boundary Explorer (IBEX) spacecraft last year to investigate the edges of the heliosphere — the insulating bubble the sun creates around the solar system. IBEX principal investigator David McComas reports on the first surprising results.

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IRA FLATOW, host:

This is SCIENCE FRIDAY from NPR News. I'm Ira Flatow.

A bit later, we will be talking about the climate change policy, but first, anyone ever tell you that you're living in a bubble? No, not that kind of bubble. The truth is, we all live in sort of a bubble - a huge bubble created by the sun called the heliosphere. It's a space carved out around our solar system by the solar wind, a stream of gas blowing out from the sun at millions of miles per hour into space in all directions and all the time. But eventually that solar wind slows down, our protective bubble ends, and the rest of the galaxy begins.

And last year around this time NASA sent up a spacecraft called the Interstellar Boundary Explorer, the IBEX, to investigate what's going on at those outer limits where the heliosphere meets that galaxy. And now the results are in, published this week in the journal Science with some very unexpected twists for scientists.

Our next guests are here to us - talk about this and walk us through the findings, and if you'd you like to talk about it, our number is 1-800-989-8255, excuse me, 1-800-989-TALK. You can tweet us @scifri.

David McComas is the principal investigator for NASA's Interstellar Boundary Explorer's spacecraft, the IBEX. He's also assistant vice president of the Space Science And Engineering Division at Southwest Research Institute in San Antonio, Texas. Welcome back to SCIENCE FRIDAY.

Mr. DAVID MCCOMAS (Southwest Research Institute): Thanks, Ira, great to talk to you again.

FLATOW: Thank you. Let's go step back for a minute and talk about the heliosphere in general. Why is it there and what does it do for us?

Mr. MCCOMAS: Okay, well, actually your summary was very good. The heliosphere is really there because we have a sun with a very hot atmosphere called the corona that boils off into space all the time. And that boiling off corona produces a wind that we call the solar wind of hot ionized gas that flows out a million miles an hour and inflates this bubble in space. And inside the bubble, the heliosphere, is basically material from the sun, outside of the bubble and providing pressure from the outside trying to squeeze it in, is material from the rest of the galaxy.

FLATOW: Mm-hmm. And what does this IBEX spacecraft do?

Mr. MCCOMAS: So IBEX, the Interstellar Boundary Explorer, actually measures particles, neutral particles, neutral atoms, single atoms, that come propagating in from the outer reaches of the heliosphere. It's about 10 billion miles. And these particles come in over the course of many months to a year, depending on - or a few years, depending their speed, and they're produced in this interaction region near the boundary between our heliosphere and the rest of the galaxy and these neutral particles are produced, they're neutralized there. Then they can cross magnetic fields all the way back into Earth orbit. IBEX is in a high altitude Earth orbit that goes almost out to the moon and it looks out and sees these particles coming in from distant space.

FLATOW: So IBEX can scan the sky in all directions and then make a map of these particles?

Mr. MCCOMAS: Yes, it actually took us six months to make the map. We used the spinning of the spacecraft and the fact that we have to keep re-pointing the solar panels at the sun…

FLATOW: Yeah.

Mr. MCCOMAS: …over the course of six months to view the entire sky.

FLATOW: And you saw something unusual, what you've been describing as this ribbon that would around the whole map here?

Mr. MCCOMAS: Yeah, unusual is maybe not a big enough word. It's really shocking. We expected to see, based on theories and models, we expected to see variations in the number of particles or the flux of particles coming in from these outer reaches. And we expected those variations to be relatively small, into tens of percent and to vary over very large angular ranges. And instead what we saw was a very narrow structure that we call a ribbon, where the fluxes and other particles coming in are two or three times that of any other part of the sky.

FLATOW: Do you know why that is?

Mr. MCCOMAS: We don't really know why that is. The theories and models include a lot of the effects that we thought were important out there. There were no predictions of a narrow structure like this ribbon, but we have learned that the ribbon appears to line up with the direction in space where the external magnetic field, the field outside out heliosphere, into local interstellar medium, where it basically drapes around and squeezes hardest on our heliosphere. And so through some as yet unidentified physical process, there seems to be a connection between those two things.

FLATOW: As yet unidentified physical pro - object…

(Soundbite of laughter)

Mr. MCCOMAS: It's a process. I mean, we know there's a correlation between the two…

FLATOW: Yeah.

Mr. MCCOMAS: …you know, this interstellar magnetic field was determined based on other independent observations and we basically see this ribbon, and when you say, okay, what orders the ribbon, what, you know, what lines up with the orientation of this ribbon, it's this external magnetic field. So somehow, somehow its squeezing on the heliosphere causes something to happen where we collect two or three times more particles, right along this narrow structure than anywhere else.

FLATOW: So the struc - these particles are coming in from outer space, if I could draw myself a picture. They're coming in from outer space and some process is making them sort of line up in a narrow channel.

Mr. MCCOMAS: Right. Probably - probably the source is actually higher density out there. Most likely there's the ribbon of particles coming in is actually reflecting a ribbon of high density out of the interaction.

FLATOW: Mm-hmm. And where are the particles coming from? Any one place from space or just from out there?

Mr. MCCOMAS: Well, the solar wind as it expands out, and it expands out to about 10 billion miles, it goes through a shock, something we call the termination shock, where it slows down and starts to turn around and get diverted away from the interstellar material. In the space between that shock and the boundary of the heliosphere, the gas becomes heated and becomes slower. And that's the region that these neutral particles are produced and come radiating back in towards us from.

FLATOW: Mm-hmm. I noticed, in reading your paper and watching your news conference on this, that you showed where the two Voyager spacecraft are located, one in - and right out there, right in the middle of this ribbon, and they were launched in the '70s and they totally missed it, it seems.

Mr. MCCOMAS: Yeah, the Voyagers are just great space craft…

FLATOW: They're still working?

Mr. MCCOMAS: Oh, yes. Yeah, they're still working and they're returning great observations, and we know a lot about this interaction region of the two locations of the Voyagers, and that was part of what was so shocking to us. We thought we knew a lot more because we have these good local measurements from this two spacecraft. And then when we, as we started to build up the image of the sky, we went, wow, look at that. The most interesting, surprising thing in the whole sky actually kind of snakes between the two. And both of the Voyagers miss it.

FLATOW: Wow. And that's because it's like having just a couple of outposts…

Mr. MCCOMAS: Yeah, the analogy that we like to use is it little bit like having two weather stations on the ground. You know, maybe have one in San Antonio, where I live, and maybe have one in New Orleans. But you can have a hurricane come through and hit Houston and not necessarily measure it at either one of those two locations. So IBEX is very much like having a weather satellite finally where you can look down on the whether fronts and see the whole global picture.

FLATOW: Mm-hmm.

MCCOMAS: Instead of just having local measurements that you're weather stations.

FLATOW: Now, you were talking about - this was collecting data over six month period. Does the ribbon change shape over that period of time?

Mr. MCCOMAS: That's a great question. It takes us six months to make the full image because of how the spacecraft makes it. We are now collecting observations in the second sky map. And while we haven't publish those results yet, what we have said about it is that the ribbon is still there but that there appears there maybe some variations from one six month to the next six months.

FLATOW: And why would our current theories about how our galaxies interact with the universe, why would they not predict this ribboning effect? What do we have to change now about how we look at our own galaxy - solar system?

Dr. McCOMAS: If I knew the answer to that, I'd be writing that paper today.

(Soundbite of laughter)

Dr. McCOMAS: There's really something very fundamental in this interaction, something in - you know, we have a lot of physics in these models and simulations. There's really something very fundamental that we're missing. There's a piece that we haven't included, that we haven't understood yet, and the community as a whole is rushing like crazy now to try to figure that out.

FLATOW: Could it be something as mysterious as the dark energy out there, dark matter, dark energy?

Dr. McCOMAS: It's probably not related to that. It probably has to do with how ionized particles collect in regions and how you can get higher-density regions in some places than others, maybe how the magnetic field is configured. It's probably not related to dark energy although, you know, as a scientist, I have to tell you that until we understand something, it's very important for us to sort of leave as many options open as possible. Sometimes these things are really surprising.

FLATOW: Let's go to Sue in Port Charlotte. Hi, Sue.

SUE (Caller): Hi.

FLATOW: Hi, there.

SUE: My question is - I'm not sure, I don't know where your funding comes from, whether it's private funding or from the government, but I'm wondering, also from the man that was speaking just a little while ago about the moon and landing the…

FLATOW: Sue, I'm running out of time. You've got to get your question in.

SUE: My question is: Is there some kind of a positive need for this, as far as humanity goes? Will this help humanity in some way on the whole?

Dr. McCOMAS: Okay, so Sue, that's a great question. So this boundary, this interstellar boundary actually is a very important region for us. It provides protection from the vast majority of the cosmic radiation, the galactic cosmic rays that are running around outside in the rest of the galaxy. And, for example, about 90 percent of the galactic cosmic rays at 100 million electron volts - which is a measure of energy - about 90 percent of those are actually shielded out by this interaction region.

That interaction region has probably changed over time and will probably change again in the future as we go through different exterior conditions. And only by understanding it can we understand how those variations have happened and are likely to happen going forward.

SUE: (unintelligible)

Dr. McCOMAS: Right now, we're at a point where the galactic cosmic rays are at about the highest level that we've measured since the space age, and they've been going up because we're in a very extended solar minimum.

Understanding this interaction will help us understand whether we can do manned space flights, for example, further out in the solar system and tolerate the radiation from the galactic cosmic rays.

FLATOW: Okay, Sue?

SUE: (unintelligible). I mean, is that part of the issue?

FLATOW: What's that?

SUE: Is it a cause for cancer?

FLATOW: I'm not sure what that meant.

(Soundbite of laughter)

Dr. McCOMAS: Cause for cancer, on the face of the Earth, in humans, no, I don't think so. This is more radiation out in space for manned space flight.

FLATOW: And that is a big - thank you, Sue. That is a big problem for going out there in space, is it not?

Dr. McCOMAS: That's right. One of the big things that you have to deal with is how much radiation your astronauts can have.

FLATOW: Well, Dr. McComas, thank you for taking time to be with us today.

Dr. McCOMAS: Thank you, Ira.

FLATOW: Dave McComas is the principal investigator for the NASA IBEX spacecraft and assistant vice president of the Space, Science and Engineering Division at Southwest Research Institute in San Antone, Texas.

We're going to take a break, and when we come back, we're going to change direction and talk about climate change. The U.N. Summit on Climate Change is going to - is said to take place in Copenhagen, Copenhagen, if you wish. We'll come back and talk about what to expect is going to happen at that meeting. So stay with us. We'll be right back after this break.

(Soundbite of music)

FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY from NPR News.

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