IBEX Spacecraft Intercepts 'Alien' Particles

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As it circles Earth, NASA's Interstellar Boundary Explorer hunts for particles streaming in from beyond the solar system. It has intercepted hydrogen, helium, neon and oxygen atoms. IBEX principal investigator Dave McComas discusses how the abundance of those atoms hints at the Milky Way's composition.


This is SCIENCE FRIDAY. I'm Ira Flatow. Has anyone ever told you you're living in a bubble? Well, technically we all are, a huge bubble in space called the heliosphere, inflated by the sun and the blowing of the solar wind. Good thing it's there because that bubble protects us from dangerous stuff like cosmic radiation from the galaxy.

But what is it like out there beyond the bubble? NASA's interstellar boundary explorer, IBEX, has been intercepting particles from that great beyond, and we're learning that our Milky Way neighborhood may be a little bit different than we thought it was, findings that are appearing this week in the Astrophysical Journal and reported at NASA.

David McComas is principal investigator for the IBEX mission. He's also assistant vice president for the Space Science and Engineering Division at the Southwest Research Institute in San Antonio. He joins us. Welcome back to SCIENCE FRIDAY.

DAVID MCCOMAS: Well, thanks, Ira, it's great to talk to you again.

FLATOW: So tell us what IBEX was looking at there.

MCCOMAS: Yes, so IBEX is actually measuring particles which are coming in from beyond our heliosphere, this region of space, as you described, that is a bubble; it includes the solar system, it includes the Earth and all the other planets, and is inflated by the million-mile-an-hour solar wind that blows out from the sun all directions all the time.

And as we travel through the local part of the galaxy, different material tries to come in because we're sort of plowing through it like a snow plow. The charged part can't come in because the magnetic fields from the sun basically hold it out. But the neutral particles aren't affected by magnetic fields, and they come right in.

It takes about 30 years for them to cross 15 billion miles from the boundary all the way to the Earth, and we're able to measure these very rare particles with the IBEX spacecraft.

FLATOW: And are you finding any surprises about these particles?

MCCOMAS: It's absolutely fascinating. We've learned a variety of things. First, we've learned that the wind is coming in at a significantly slower speed than we thought. Previous measurements from about 15 years ago, by the only other spacecraft that could measure any of these particles, indicated that the speed was 59 or 60 thousand miles per hour.

We measure it at about 52,000 miles an hour and from a slightly different direction than people thought before.

FLATOW: That's some headwind.

MCCOMAS: That's quite a headwind, it certainly is.


MCCOMAS: Perhaps more importantly, though, for the first time we're able to measure other elements, and in addition to helium, which was measured before, and which we measure again, we've also measured hydrogen, oxygen and neon. And in particular, the oxygen and neon are very critical because those heavy elements are not from the big bang and from the start of the universe, but they had to have been made in prior stars, burning lower - less massive stuff into these heavy elements and then having novas and supernovas and being spread around the galaxies.

FLATOW: So they're really traveling, as you say, far away, from far-away distances to get here.

MCCOMAS: Tremendous distances. Even once they enter our heliosphere, it's still a tremendous distance to cross the 15 billion miles to get here.

FLATOW: And do they have any kind of signature to them that will give you some information, besides just that they - the particles are unusual?

MCCOMAS: Well, the real signature comes in the ratios of the different types of particles. Now that we can do oxygen and neon and compare those two, what we've learned is that the region outside of the heliosphere, outside of the solar system, right around us, is deficient in oxygen.

There's significantly less oxygen than we expected, and that's a big surprise and could have some pretty big implications. We don't yet know whether that's because the sun may have formed in a really different part of the galaxy and not have the same composition as other parts of the galaxy, or maybe it's telling us that the oxygen is somehow locked up in ices, you know, like water ices on dust grains in interstellar space.

But either way, it's going to require a rethinking of how this material moves around the galaxy and forms future planetary and stellar systems.

FLATOW: So that really is a head-scratcher then.

MCCOMAS: Absolutely.

FLATOW: And what kind of re-thinking would you have to do?

MCCOMAS: Well, I think the re-thinking comes into how uniform different star systems, including their planets, might be. You know, ours is a particular mix of elements, and it came up with enough water here on Earth, for example, for life to develop and that sort of thing.

But maybe that oxygen content is quite different in different star systems. Maybe there's more oxygen or less oxygen, and you can end up having different sorts of stars and planetary systems forming.

FLATOW: What about heavier elements? Are they coming in also? Would we expect to find them?

MCCOMAS: Even heavier than the neon and oxygen?


MCCOMAS: Sure, undoubtedly all of those elements are coming in in some amount, and if you waited long enough, I don't know how long it would be, 100 years or whatever, you might even see a single gold atom come in. But basically there's a different amount of these materials in the galaxy, and so far what we've seen is four of the five most abundant elements.

We don't see carbon. Carbon is also very abundant, but it's easy to ionize, and so the carbon that comes into the heliosphere gets ionized; that is, the electron gets removed, and it becomes swept out by the solar wind. So we're basically looking at the most abundant heavy elements.

But over time, IBEX may actually be able to measure some other ones.

FLATOW: You talked about this interstellar wind at 52,000 miles per hour.


FLATOW: Where is that coming from?

MCCOMAS: Well, that's really a combined speed. I like to think of it in terms of - think of an airplane, maybe a slow-moving airplane flying through clouds. There's the motion of the airplane with respect to the ground, and then there's the motion of the clouds moving around in the sky.

And if you sat on that airplane and said what direction is the gas, is the air, the clouds coming at me from, you would do an addition, a vector addition, but you'd do an addition of those two motions in order to get the relative motion of the cloud with respect to you.

And exactly the same thing is happening to us in the galaxy. The sun is moving through the galaxy, basically going around the galaxy, and the local clouds around us are moving around. And so there's a vector addition of the motion of the local cloud and of our proper motion with respect to the galaxy, and that combination makes this headwind of 52,000 miles an hour.

FLATOW: Now, these clouds are not like the kind we see outside of our airplane, though.

MCCOMAS: No, no, these are clouds of different types of interstellar material. Some are very dense. Some are very tenuous. In fact, another big finding from IBEX this week is that we're still in a cloud we call the local interstellar cloud. Previous measurements had suggested, when we thought it was a higher speed, that we maybe already outside of that cloud and in some unknown boundary region between that cloud and the next cloud, something we call the G Cloud, because it's towards the center of the galaxy.

But anyway, these measurements we find at 52,000 miles an hour, that falls right in other observations that were made of this local interstellar cloud, remote observations, and that tells us we're still right in that cloud, although within the next - somewhere between 100 and maybe 4,000 years, we should be leaving this local interstellar cloud and heading into the G Cloud.

FLATOW: Wow. Let's go to the phones. Gary(ph) in D.C. Hi, welcome, Gary.

GARY: Hi. I wanted to know about the shape of the heliosphere. Is it spherical, or is ovoid? And one other quick question: Will future space missions include some instruments to help measure the sun's effect on the Earth, even if those missions are dedicated to other purposes? Thank you.

FLATOW: Thank you, Gary.

MCCOMAS: Those are two great questions. Let me take the first one. The shape of the heliosphere we've already learned a lot about from IBEX, and in fact when I was on a year and a half ago with you, Ira, we talked about the initial results from IBEX that showed that the external magnetic field in the interstellar medium sort of squeezed the heliosphere and made it kind of oblate, a squashed shape.

Part of what we're learning with the new results from IBEX, just announced this week at the NASA press conference, is with this lower speed, the sort of bullet-shaped nose of the heliosphere is probably broader and flatter because there's not as much pressure from the motion.

And so, again, the effect of the magnetic field is probably stronger. So it's kind of a mixed shape. It's not a sphere, but it's not really completely bullet-shaped either because of this strong squeezing by the external magnetic field.

FLATOW: Now, we know that the two longest, I guess, lived spacecraft that are still working out there, among the two, are the Voyagers.


FLATOW: They're still out there sending data back?

MCCOMAS: They are, and this is so exciting for us because we have IBEX in Earth orbit looking out, making the global picture of the heliosphere, I mean getting data from all directions in space, and now getting these interstellar neutrals coming in from the local part of the galaxy.

And at the same time, Voyager 1 and Voyager 2 are out in the very far reaches of the galaxy, about 35 degrees north of the nose and about 30 degrees south of the nose, and they're taking local measurements out - still inside the boundary of the heliosphere but getting darn close to the edge of the heliosphere.

And so between the two, the two local measurements and these global observations from IBEX, we're really being able to put together the full picture of this interaction for the first time.

FLATOW: And they're coming up on 40 years of age, aren't they?

MCCOMAS: And they are. They're remarkable spacecraft.

FLATOW: And what keeps them going out there? Do they have their own little power sources that keep them - like the bunny rabbit, they're still going?

MCCOMAS: They do. They have RTGs, which are radioisotope nuclear generators, basically, not like a reactor, but they basically make heat from nuclear material, and that's used to make electricity to power the spacecraft.

FLATOW: It's amazing we can still hear them, that they go - we talked last week about how our sun goes through cycles. Does the heliosphere also change in shape and size depending what the sun's doing?

MCCOMAS: Another great question. The answer is it must, but we haven't seen it do that yet. We've taken the first three years of observations with IBEX basically through a very prolonged solar minimum. Now the sun has become active again, we're headed towards a solar maximum, and fortunately with IBEX, which was initially only supposed to be a two-year mission, it was a very small, inexpensive mission, but we were able to put it in an orbit where we think it may last for a decade or more.

We should be able to watch the 11-year solar cycle, and since the heliosphere is inflated by this million-mile-an-hour solar wind from the inside, as that solar wind varies from solar minimum conditions to solar maximum conditions, it ought to change how the inflation occurs and what the overall heliosphere is like.

FLATOW: Now, I was fascinated how much that we still don't know about our closest neighbors, something like the sun. We just don't understand the mechanics fully, do we?

MCCOMAS: No, we don't, and the study of heliophysics, which is the study of the science, the physics from the sun all the way out to these outer boundaries of the heliosphere, is a - you know, is a fascinating area where we're making new discoveries every day.

FLATOW: Well, we wish you good luck, and we'll be checking back with you periodically.

MCCOMAS: Well, great. I enjoyed talking to you again, Ira, thank you.

FLATOW: It's good that the IBEX is surviving so long, and we've got 10 years to look forward to. That's terrific.

MCCOMAS: We do. Thanks.

FLATOW: Thanks a lot. David McComas is principal investigator for the IBEX mission. He's also assistant vice president for the Space Science and Engineering Division at the Southwest Research Institute in San Antonio in Texas.


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

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