AUDIE CORNISH, HOST:
For 35 years, a lonely spacecraft has been making its way toward the edge of the solar system. Voyager I is almost there. According to NASA, the spacecraft has reached a new region in the solar system called the magnetic highway. It's a crossroads of sorts between charged particles that zoom around the sun and charged particles from outside the solar system.
Now to help us better understand all of this, we turn to Ed Stone. He's chief scientist of the Voyager Mission. Ed Stone, welcome to the program.
ED STONE: Yes, happy to be with you.
CORNISH: So help us understand, let's place the Voyager on an imaginary map, how close is it to leaving our solar system?
STONE: We don't know exactly but we could be a few months away or maybe several years. But Voyager 1 now is 11 billion miles from the sun. It's 122 times further from the sun than the Earth is, so it's really out there.
CORNISH: And as we mentioned earlier, this new region you're calling the magnetic highway. Explain exactly what does that mean?
STONE: Well, the magnetic field of the sun is carried out by the supersonic solar wind; it's the atmosphere of the sun expanding outward a million miles per hour. And because the sun is rotating, the magnetic field - which remains anchored on the sun - gets spun out into a giant spiral.
And we are still on the sun's magnetic field lines. But, in fact, those field lines now have connected to the outside so that what's inside can disappear into interstellar space outside. And what's outside in interstellar space can zoom in along the magnetic field.
CORNISH: So it's like we're inside a big bubble essentially and Voyager is getting toward the edge of that bubble?
STONE: Yes, it's a very large bubble and we're very close to the edge. Once we leave the bubble, Voyager 1 will be in interstellar space; the first spacecraft to actually leave the bubble and move to the space between the stars.
CORNISH: So, this path in and out - the magnetic highway - a surprise that you found it?
STONE: Yes, we didn't really expect to find the highway. We were expecting that when we got to the edge, we would see the inside particles disappear and that the outside particles would be full intensity, and the magnetic field would be in a different direction - because outside, the magnetic field comes from the other stars, not from our own sun.
And even though we did see the inside particles disappear, and we did see the particles from the outside come in, we are still in the solar magnetic field. That we knew only once we could analyze carefully the magnetic field and that was not really done until about two weeks ago.
CORNISH: And what will you be looking for that will tell you that, yes, the Voyager has made it out?
STONE: Well, the key will be the magnetic field. We know the field inside is from the sun and it's now east-west, because that's the way the spiral winds around the sun. Outside, all of our information we have indicates that the field is more like a north-south field. So we should see a switch in the direction of the field from what it has been to some new direction. And that will be a key signature that we have finally left the solar bubble and entered interstellar space.
CORNISH: What's the significance of what you've learned about this magnetic highway?
STONE: The magnetic highway is part of how our heliosphere is interacting with what is outside. And the heliosphere is in one sense protecting all of us from what's outside. And we need to understand how the size of our heliosphere depends on how strong the wind from the sun is blowing outward, as well as how strong the interstellar winds are outside which are compressing it.
And so, we're beginning to understand in detail how that interaction takes place. And it is, in fact, more interesting then our simple models suggested.
CORNISH: Ed Stone, thank you so much for speaking with us.
STONE: Well, thank you.
CORNISH: That's Ed Stone, chief scientist of the Voyager Mission, talking about the so-called magnetic highway Voyager 1 has reached at the edge of the solar system. Transcript provided by NPR, Copyright National Public Radio.