365DaysDate: March 9, 2009


Title: Voyager: Sailing to the Edge of Our Solar System

Podcaster: Jane Platt, with Dr. Ed Ston

Organization: NASA’s Jet Propulsion Laboratory

Description: NASA’s Voyager 1 and 2 spacecraft, launched in 1977, are headed toward our solar system’s “exit sign” en route to becoming the first human-made objects to enter interstellar space. The Voyagers have already beamed back a wealth of images and information about the planets and moons inside our solar system. In this podcast, Voyager Project Scientist Dr. Ed Stone of Caltech recaps some mission highlights and describes conditions facing the Voyagers as they leave our solar system. The podcast includes brief excerpts of space sounds recorded by the mission, and greetings from Earth carried by the two spacecraft

Bio: Jane Platt is News Chief of the Media Relations Office at NASA’s Jet Propulsion Laboratory in Pasadena, California. During her prior career in broadcast journalism, she was the West Coast correspondent for ABC Radio Network, and a reporter for other networks and radio stations. She covered such varied stories as earthquakes, fires, high-profile trials, riots, Academy Awards, Space Shuttle landings, the Voyager Neptune flyby, and a total solar eclipse. Jane draws on this broadcast news background in her current job, providing information for journalists covering JPL missions and science discoveries, and creating and producing podcasts for JPL.

Today’s Sponsor: This episode of “365 Days of Astronomy” is sponsored by William Duncanson in appreciation of all the work our team is doing for the IYA and Astronomy Cast. Thanks William!


Music open.

Platt:  Sailing to the edge of our solar system….

I’m Jane Platt with NASA’s Jet Propulsion Laboratory in Pasadena, California.

For nearly a third of a century-since 1977-the Voyager 1 and 2 spacecraft have been cruising through the solar system.  And they’re still going strong near the edge, preparing to break on through to the other side.

Stone:  Our sun has a wind blowing a million miles per hour, radially outward from it, and it creates a bubble around itself called the heliosphere.  All the planets are deep inside of this bubble, in fact the two Voyager spacecraft are still inside this bubble, trying to exit and reach interstellar space for the very first time.

Platt:  Voyager Project Scientist Dr. Ed Stone of Caltech-the California Institute of Technology in Pasadena.  How will we know when the Voyagers leave our solar system?

Stone:  Well, the two Voyagers are now in the final layer of this bubble.  It’s where the supersonic wind has suddenly slowed down and is now turning around to flow down the tail of the heliosphere, because it’s a comet-shaped like object.  Once we reach the heliopause, the boundary between our solar wind and the interstellar wind, we will see the magnetic field change, we will see the flow of the plasma, the ions change, and we will probably see a change in the energetic particles coming from the galaxy, because they can’t get inside of our heliosphere.

Platt:  So what’s it going to be like out there in interstellar space for the Voyagers?

Stone: Surprisingly, we actually know that there is a wind out there.  We can observe it inside, in fact it can be observed from Earth, Earth’s orbit.  So we know there is a wind  coming from a particular direction, which is then pushing and deforming the heliosphere into this comet-shaped like object.  We also know there’s a magnetic field out there, and now from Voyager we have our first estimate of the direction of that magnetic field and how strong it might be, although these are just estimates at this  time, and we won’t really know until we get there.  There, of course, the material, the wind which is out there is coming from other stars, from the explosion of other stars, rather than from our sun.  Until now we have been immersed in the wind from our own sun.  Once we cross the heliopause, we will for the first time be immersed in matter that has come from other stars.

Platt:  There’s no exact timeline for when the Voyagers will leave the solar system, but Stone says they have an idea.

Stone:  In the solar system we measure distances by the distance from the Earth to the sun, that’s one astronomical unit-93 million miles.  Neptune is at 30 astronomical units, the outermost planet.  Voyager is now at 109 astronomical units, that’s three times further away from the sun than the outermost planet and still inside the bubble.  But I think that we’re likely to reach the edge of the bubble sometime in the next five or six years, and for the first time be in interstellar space.

Platt:  Within our solar system, the Voyagers have revolutionized our understanding of planets and moons.

Stone:   Along the way we discovered the remarkable diversity of the bodies in the solar system.  We found volcanoes on the moon Io, the first evidence of active volcanism outside of the Earth.  Titan, at Saturn, we found a very dense atmosphere where it was suggested that there might be methane, natural gas raining down on its surface. On to Uranus, which is tipped on its side, we found a tiny little moon which had one of the most complex surfaces in the solar system.  And finally at Neptune, the last body we visited was Neptune’s moon Triton, which is 40 degrees above absolute zero, and even there we found activity in the sense of geysers erupting from its icy surface.

Platt:  Ed Stone believes the Voyagers have opened our collective human mind about the solar system we call home.

Stone:  What the Voyagers have done is show us things that we had no idea were there.  We had really no idea that we would see active volcanoes on another world, on a small moon, actually.  So it’s that kind of opening up one’s perspective to realize that the solar system is much more complex and much more diverse than our own imaginations, thoughts, gave us a clue.

Platt:  The Voyagers have beamed back spectacular images through the years — but there have also been some pretty eerie sounds.

(High-pitched sounds)

Platt:  Those are plasma waves from around Jupiter.  Oh, and in case the Voyagers should encounter someone or something out there, they’ve got sounds of their own to share–on a Golden Record.

(Sounds of greetings in several languages, starting with “Hello from the children of Planet Earth”)

Stone:  We knew that these spacecraft were going to leave the solar system forever.  They’re going to be in orbit around the center of our galaxy, just like our sun is.  So we decided we should try to create a picture, if you like, a description of Earth, not only of humans, but Earth itself, so there are pictures of various aspects of Earth, there are sounds of Earth, there’s music from Earth, there’s language from Earth, all saying “This was the civilization, this was the place that created this vehicle.”

Platt:  In your personal opinion, do you think any beings will hear that Golden Record at any point?

Stone:  I think it’s highly unlikely that anyone else will ever hear that record.  But it’s a message for us here on Earth.

Platt:  More information on the Voyagers is online at  If you’d like to hear more JPL podcasts, visit .

End of podcast:365 Days of Astronomy
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