Planetary Radio: Space Exploration, Astronomy and Science - Ed Stone and Forty Years of Voyager in Space

Episode Date: August 16, 2017

It is most space fans’ favorite planetary science mission, and with good reason. We visit with the man who has been in charge of Voyager mission science for more than four decades.Learn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

The Voyager mission celebrates 40 years in space, this week on Planetary Radio. Welcome, I'm Matt Kaplan of the Planetary Society with more of the human adventure across our solar system and beyond. A special streamlined edition of the show as I prepare, along with much of the Western Hemisphere, for the August 21st eclipse. No worries, though, you're about to hear a conversation with the great Ed Stone, project scientist for the Voyager Interstellar Mission, thought by many to be the greatest planetary science mission of all time. And Bruce Betts will still join us for What's Up, and one of those rare occasions that will let a few more of you get in

on the space trivia contest. At 81, Ed Stone remains a very busy guy. He is David Morisseau Professor of Physics at the California Institute of Technology, where he is also Vice Provost for Special Projects. He still has Caltech's Space Radiation Lab, too, but his longest tenure, as you'll hear, is his service as project scientist for the Voyager mission. The first of the twin spacecraft was launched on August 20, 1977. Nearly 40 years later to the day, Ed joined me on Skype for a conversation about this anniversary, the mission's accomplishments, and his own legacy that includes running the Jet Propulsion Lab. Ed, welcome back to Planetary Radio. This is your fifth time on the show.

I am just as honored as I have ever been to have you as our guest. Thank you for doing this. It's always a pleasure to talk with you. The last time we talked, I think, was when we did a live show, Planetary Radio Live, for the 35th anniversary. It's hard to believe we're now at the 40th. Yes, time just keeps moving on. It's really quite remarkable. It does do that, as do the Voyager spacecraft. I hope you understand the adulation that these missions have received. I mean, I know you've been a witness to it.

Are you familiar with the little poll that the Planetary Society did a couple of years ago? We work with this artist who runs a store that puts out posters, and he wanted us to run a poll to help pick the three most popular planetary science missions of all time. And the winner, no surprise, hands down, Voyagers 1 and 2. Wonderful. The science continues to flow in. We're going to see the 40th anniversary of Voyager 2's launch just four days after this conversation goes public. Did you or anybody else imagine that we would reach this kind of magnificent milestone?

We all had our hopes that one of the spacecraft at least might reach interstellar space, but we had no idea how far that was, nor did we have any idea how long a spacecraft could last. The space age itself, when Voyager was launched, was only 20 years old. So this is now twice the age as when launched, the space age. You know, somebody just pointed that out to me yesterday, that the Voyager mission spans such a huge portion of the space age itself. That's right.

It's really been a mission that just keeps going and keeps discovering. It's not just that it keeps going, but it's doing new things, bringing back new information about now what's outside the heliospheric bubble the sun creates around itself. I want to come back to that in a moment. JPL just, I think yesterday, put out a list of at least some, maybe all of the Voyager firsts. It is an awe-inspiring list. If you break it down, including all of the worlds, the moons that Voyager discovered, there are something like 50 different achievements that you could point to just out of this list. And I bet there are a lot more. Yes, well, the mission every day during the encounters was many discoveries every day, day after day.

It was a very exciting time. And, of course, there's been still more work done with that data in the years since that. And then Voyager started on its interstellar mission, which it finally reached interstellar space in 2012, 35 years after launch, and now it's exploring a region no other human object has ever been to before. So there is no doubt now that Voyager 1, at least, has indeed passed into the space between the stars and beyond the heliosphere. I think most of us now feel that we have the evidence that we're outside. Inside,

the material comes from the sun and the magnetic field comes from the sun. Outside the bubble, the plasma bubble, the material comes from the explosion of other stars, supernovae, and the magnetic field is that of the Milky Way galaxy. So we are in a new regime. Voyager 2 is on a very different trajectory, of course. Are there going to be benefits for science because it, when it does exit the heliosphere, it will be in a very different spot from Voyager 1? That will give us some impression about how spherical the heliosphere really is. It's not a sphere. It's more like a comet-shaped object with a blunt nose, and Voyager 1 is near the nose, Voyager 2 is off on the flank, so we expect that there will be some

significant differences about the flow and the magnetic fields in that region of the interstellar space. We have an instrument on Voyager 2 that is not working on Voyager 1. That's the instrument which measures the plasma wind, the solar wind itself. And so we now have measurements that we did not have of how the wind from the sun, which was originally radial, has now turned to flow in the direction of the tail. Is that blunt, forward-looking surface of the heliosphere, is that related to the sun's progress around the center of the galaxy?

Yes, it's a combination of the motion of the Sun relative to its neighbors, but it also involves the direction of the cloud of material that was ejected from the supernova, which blew up about 5 and 10, 15 million years ago. And the combination of those two directions is the direction that impacts the heliosphere. What have we learned about how space itself is different outside the heliosphere than here inside where we live? Well, let me give you one example, and that's the cosmic rays, which in fact are accelerated during the supernova. They fill the space between the stars, and some of them can get into the bubble and actually get all the way to Earth. They're called galactic cosmic rays. But the slower ones can't get in. So we had no good idea what the intensity of cosmic rays is outside compared to what it is at Earth.

What we discovered is that only a quarter of what's outside actually reaches Earth. And so the heliosphere is sort of our radiation shield. This helps protect the planets from the more intense radiation environment that is outside in interstellar space. Speaking of radiation shields, Voyager has one. Has that helped it to survive as long as it has? Voyager had the very good fortune, in one sense, of flying by Jupiter, which is a very intense radiation environment, and much more intense than anything it's experienced since.

So having survived that real test, the spacecraft has had a very nice long life. When you look back at those earlier decades, when the Voyager spacecraft were still making all those discoveries within the solar system, do you have any favorites? Do you have any special pets in that long list? Well, there are many, many, of course. And I think the principal thing Voyager did, besides all the individual discoveries, of course, and I think the principal thing Voyager did, besides all the individual discoveries, was reveal, in fact, how complex and distinctively different the bodies in the solar system are. They could have all looked more or less like one like the other, but the moons are all distinct.

In fact, some of them, for instance, Io, have an active life. Before Voyager, the only known active volcanoes in the solar system were here on Earth. And then we flew by Io, that's a moon of Jupiter, about the size of our moon, and it has 10 times more volcanic activity than Earth. And so we go from believing Earth was the most volcanic, the active place in the solar system to, well, yeah, there's a little moon with 10 times more activity. That's just an indication of the surprises and the discoveries that were ahead of us during our journey past the planets. I'm so glad that you brought up Io, because I wanted to ask you about that.

It was unexpected and almost, I mean, not accidental that this discovery was made. But do you remember, can you recall how you learned that your spacecraft had picked up this image of a volcano erupting on this moon? Yes, this happened actually after our closest approach and after the press conferences had been completed, actually. It happened, the closest approach was March 5th of 1979, and it was on March 9th at the end of that week when Linda Morabito, who is a navigation engineer, was looking at images taken of Io against a star background. In order to see the stars, you need to have very long exposures, which makes the moon just bright and light. But in fact, that meant you could see these fainter eruptions, a plume 200 miles high erupting from the surface of the moon. Did Voyager also give us the first clues that there might be oceans, internal oceans around the solar system? Yes, once more. Before Voyager, the only known liquid water ocean was right here on Earth.

the only known liquid water ocean was right here on Earth. And then we flew by Europa, which is right next to Io, and so basically a twin in the sense of its size, but not in the sense of its surface. It doesn't have any volcanoes that we can see, at least. What it has is ice on a liquid water ocean. Now, Voyager couldn't prove that there was a liquid water ocean. It could only suggest that from the cracked ice that we saw. And that's what the Galileo mission subsequently was able to do was say, yes, there is a liquid water ocean. In fact, there's a lot more water and ocean on Europa than there is on Earth. Do you have any contact with your colleagues at the Jet Propulsion Lab and Caltech who are now working on that return to Europa with the Europa Clipper? How do you feel about that mission?

I think it sounds very exciting because, as you know, anywhere here on Earth that there's liquid water, be it nearly boiling water at the bottom of the ocean or freezing water in Antarctica or acidic water in the river streams, there's life, microbes alive. So I think that one of the main objectives is to find liquid water in the solar system, or at least where there was liquid water, there may be some historic evidence of life. So I think there's a lot of interesting opportunities now in the solar system. That's Caltech professor, former JPL director, and Voyager mission project scientist, Ed Stone. Our conversation will continue after a break.

This is Planetary Radio. Planetary Society t-shirts, posters, and more. Visit planetly.com to learn more. That's planet.ly. forward slash space shop make sure everyone is ready for the 2017 North American Total Solar Eclipse. Together, we've created the new Junior Ranger Eclipse Explorer Activity Book. It helps kids learn about the science, history, and fun of eclipses. Call your nearest national park and ask if they have the Eclipse Explorer Book, or you can download it from mps.gov slash kids or at planetary.org slash eclipse. Welcome back to Planetary Radio. I'm Matt Kaplan, celebrating the Voyager mission's 40th anniversary with the man who has been its project scientist for all of those years

and five more before launch. I had more mission highlights to ask Ed Stone about. First, though, a recommendation. I've just seen a wonderful documentary called The Farthest Voyager in Space. It's a glowing tribute to this mission, told largely at the personal level by many of the men and women behind it, including Ed. The Farthest premieres on PBS August 23rd, and then will begin a limited theatrical release in an expanded version. We've got a link on the show page at

planetary.org slash radio. As I think you know, one of our founders at the Planetary Society, Carl Sagan, along with a lot of other people, were very excited about Voyager getting a look at Titan. There was kind of a disappointing surprise there from what I've read. We knew the Titan had an atmosphere with methane in it from ground-based data. Titan is a satellite or a moon of Saturn. It's about the size of Mercury, so it's a pretty big object. So we knew it had an atmosphere. What we didn't know is it had a dense, deep nitrogen atmosphere like that here on Earth. It's the only other nitrogen atmosphere in the solar system.

atmosphere, like that here on Earth. It's the only other nitrogen atmosphere in the solar system. And not only with that, but the methane in that atmosphere, which is a minor component, radiated by the radiation and from the sunlight. And instead of producing oxides and smog like here on Earth, it produces organic compounds, which rain down on the surface of Titan. And we suggested that there could be lakes of methane and ethane, and that's exactly what the radar system on Cassini some decades later was able to show, because the photochemistry on Titan is so intense that it creates a haze later that we cannot see through optically. Since you've mentioned Cassini, as you know, that mission is about to end after 20 years in space. Pretty good follow-up to Voyager, isn't it? Wonderful follow-up. In orbit, they managed,

I don't know how many passes by Titan, and with the radar system could map through the clouds, through the haze layers, and see these bodies, some of them of the size of the Great Lakes here in North America. I want to go just a little bit farther out to Uranus and Neptune, which sadly, only one spacecraft has ever visited and returned some pretty spectacular images. Do you see any need for us to return to those ice giants? We should get back because we don't understand them as planets nearly as well as we do now, both Jupiter and Saturn. And on top of that, they have rings, which are distinctly different, and they have moons, each of which is quite different. Miranda, for instance, is a small moon

of Uranus, 300 miles across, but it has one of the most complex geological surfaces that we've seen. And that indicates that at one time, at one time, not now, but at one time, it had a very, very active geological history. And it's trying to understand how such a small moon with a very large surface to volume ratio could have retained and maintained such activity. You mentioned a few minutes ago the science that continues to come from images and data received in some cases decades, several decades ago. Are you someone who follows the work that's being done now, let's say in particular, on the images with the new image processing power that we have in the 21st century

compared to what was available to you in the late 70s and 80s? I certainly have seen some beautiful renditions of Jupiter in particular, and I'm aware that, in fact, now these tools, image processing tools, are available, and I think it's wonderful that people can try to now take advantage of the data that we have to see if they can improve the image quality. And a lot of this is being done by, you know, so-called citizen scientists. That's right. That's what makes it to the whole mission is one which really attracted the public interest, and now they can actually join

in some of the processing with the modern tools. Well, we can't finish this without looking toward the future. How will we eventually lose touch with Voyager 1 and 2? Will they just go out of range of the DSN, or is it going to be because those RTGs, those radioisotope thermal generators, are just going to keep cooling off? Well, yes, right. The power is provided by the heat generated by the natural radioactive decay of plutonium-238, which has an 88-year half-life. And so we know that every year, and there's some other losses as well as it ages, so we lose about four watts a year.

And that means every year now we're now in the new mode where every year we have to find something that will reduce our drawing power by four watts. So we can pretty well estimate that if nothing breaks, that we will finally end up with just about enough power to power the spacecraft itself, but nothing left for the instruments in about the year 2030. Wow. And the Deep Space Network, that incredible network of dishes all around the Earth, working with some others, I've read, will still be able to communicate in 2030? We listen every day for a minimum of four hours, hopefully for more like six to eight hours,

depending on how busy the communications traffic is from deep space. And we can use a 70-meter antenna. Or for Voyager 1 now, we can also, as a backup, use two 34-meter antennas, gang them, array them together. So I think we have a capability of returning our data rate, which is only 160 bits per second. 160 ones and zeros every second. Do you have any idea what the power of that transmission as received on Earth is? What tiny fraction of a watt we're actually receiving? Well, my recollection is something like a billionth of a billionth of a watt. Good Lord.

So this brings up something that I hadn't realized until JPL put out another press release based on the Voyager mission just the other day, and that is how the spectacular capabilities of the deep space network that we see here in the 21st century, a lot of that came out of Voyager. Voyager was originally a four-year mission to Saturn. Saturn's at 10 astronomical units, the Earth is at one, so 10 times further away. That means the signal strength coming back from Saturn is 1,

100 to what it would if we're just coming from nearby. And then you go to Uranus, and we lose another basically factor of four. And in order to compensate for that, we began to array our 34 meter stations in order to improve the sensitivity. By the time we got the Neptune, which is even further away, 30 times as far away as the Earth is from the Sun, then we arrayed the 27 antennas in the very large array in New Mexico and arrayed those with our 70-meter station in Goldstone. We also arrayed the Parkes antenna in Australia with our 70-meter antenna in Canberra. So, yes, we were pioneering the way of using arrays of antennas to improve the sensitivity. It makes for an even greater legacy for this mission, and I think of your own legacy as well. Has anybody else been on the mission as long as you have, 45 years now as project scientist? I think that's probably the record now in terms of on the project itself.

There are a couple of principal investigators, three of them, which are still involved, who were involved. Two of them who began to be involved almost from the beginning and would have the similar length of tenure. What part in your own mind does Voyager play in your own legacy? I know that may be something that you're not really comfortable talking about, but indulge me. I mean, you still have a lot going on at Caltech, Vice Provost for Special Projects. You've got the Caltech Space Radiation Lab and a lot of recognition, the AAS Lifetime Achievement Award just three years ago. Where is Voyager in all of this? Oh, and I left out, how could I forget, JPL director for 10 or 11 years.

Right. I've been very lucky to have been involved with a lot of wonderful projects over the years. Something which is one of the advantages of being at Caltech, it really offers opportunities such as this. Clearly, Voyager has been central to almost everything I've done. It opened the doors to these other activities, such as overseeing the construction and operation of the Keck 10-meter telescopes in Hawaii, and now basically overseeing what's going on with respect to the 30-meter telescope, which we hope will join it in Hawaii.

Yes, that's something that I very much hope for as well, and it's been talked about on this show in the past and will be again. Thirteen years before you expect to lose touch with the spacecraft. Are you expecting more surprises? I expect that once Voyager 2 reaches interstellar space, we will find that there are some distinct differences from what we thought we'd learned from Voyager 1. That's the way it's been on all of our encounters. So I'm just looking forward

to what Voyager 2 is going to tell us and how it compares with what Voyager 1 provided. Ed, I think I can safely speak for our audience and your other admirers when I repeat that it is an honor to speak to you. And I look forward to doing it again. Maybe the 45th anniversary. No, we should do it before that. Okay, I'll be happy to do it. Thank you so much, Ed. Thank you.

Time for What's Up on this streamlined edition of Planetary Radio. Bruce Betts is the Director of Science and Technology for the Planetary Society and has also been doing a lot of good eclipse stuff for us as we get ready for the big event. Some of you listening to this may have already experienced the Great American Eclipse. How about you, Bruce? Not yet. No. I don't think it works that way in my world. It'll be August 21st. But you are headed up, as we said, I think last week.

You'll be watching it from somewhere in Oregon, right? Yep, near Madras, Oregon, on the eastern side of the Cascades. So looking forward to it. It should be wild and weird and wacky. All right, what else can we look up to, even in the shorter term, in the night sky? Well, we've got Venus dominating the early pre-dawn, and it'll be a lovely view on the 18th and 19th with the crescent moon near Venus, and Jupiter still dominating the evening sky but getting quite low in the west.

And there's that eclipse that i just have to mention one more time because there's an there's an there's a total eclipse of the sun uh that will cross the u.s and uh you know north america south northern south america and the western western edge of western europe can learn more at our website at planetary.org slash eclipse including my overview of eclipses in this eclipse. You can find a link there from Recommended Reading, I believe it's called, and Emily's blog about ways you can do this with kids

and ways to make projection devices. Yeah, she has some great suggestions that we talked about a couple of weeks on this show. You can even read this stuff if it's after the eclipse. We'll let you. It's true, and a lot of it is general for eclipses. So let's move on to this week in space history. It was 1868 that there was a, yes, total solar eclipse that is particularly significant in science land

because that is when helium was first discovered in the solar eclipse on the Sun before we ever found it on Earth, as unknown spectral lines in the spectrum of the solar corona. More science coming from eclipses and from the Sun itself. Cool stuff. We move on to random space facts! I'm excited. It's an excited random space fact. In history, eclipses have been taken as everything from portents of doom I'm excited it's an excited random space fact in history eclipses have been taken as everything

from portents of doom to interestingly at least on one occasion a portent of peace according to the ancient Greek historian Herodotus an eclipse that occurred during a battle between the Medes and the Lydians I apologize for my pronunciations

caused both sides to put down their weapons and declare peace. So I've decided I will not fight with you during the two minutes of totality, Matt. Possibly since we'll be thousands of miles away from each other, not even during the entire partial part of the eclipse. I'm still looking forward to that peaceful two minutes. I'm still looking forward to that peaceful two minutes. Everyone else will be blown away by the moon and sun interacting, and you'll just be like, oh, my gosh, it's so wonderful to be peaceful with Bruce. Peace out.

Yeah, okay. We move on to the trivia contest. In all eclipse all the time, I asked you, I said, just before totality in a total solar eclipse, the sun is blocked except for sunlight streaming through lunar valleys along the limb. Who are these brief, bright beads of light named after? How'd we do, Matt? I am so hoping to see these. And the latest prediction is that we are supposed to have clear skies in Carbondale, Illinois.

So maybe I will get to see Bailey's beads. Oh, nice. Eric Rieger in Centennial, Colorado, who by the way has not won the contest in nearly two years, he said it's Francis Bailey in 1836, the British astronomer, who apparently decided what these were. What are they? They're the light that appear as you get right before totality and sunlight. The only sunlight making it past the moon is sneaking through topographic lows on the side of the moon, you know, valleys basically. Eric,

you've won. It's been a long wait, right? He's a regular listener. And so, we're going to send Eric just in time. We'll get some cheap but effective Planetary Society eclipse glasses out to him very, very quickly to go with his brand new Chop Shop Design Planetary Radio T-shirt,

the Chop Shop Planetary Society store that is at chopshopstore.com, along with, of course, a 200-point itelescope.net astronomy account. That worldwide network of telescopes operated out of Australia on a nonprofit basis. You can use them to look at anything in the sky, anywhere you like, any hemisphere of this little body we live on. Once again, Eric,

congratulations. I got some other stuff, of course. David Moulton in Orem, Utah. He said, it's interesting to me that Bailey first observed his namesake phenomenon during an annular eclipse, not a total. What is an annular eclipse? An annular eclipse is when the moon is not quite covering the entire sun, but it's still lined up central to it. So the moon has an elliptical orbit, and when it's closer to the Earth during a total eclipse, it blocks it out completely. When it's farther from the Earth during what would be a total eclipse, it doesn't quite block it all out.

So you see an annulus or a ring of sunlight surrounding the moon's circle. Excellent explanation there. From Norman Kassoun and Ilya Schwartz both mentioned that it's quite possible Edmund Halley, the other great, well, one of many other great British astronomers, that he described and correctly guessed at the cause of Bailey's beads long before Bailey gave them his name back in 1715 because there was an eclipse that year as well. So more kudos for Edmund Halley. So wait a second. So you're saying if we really attribute this correctly, we should call them Halley-Bailey beads. Sounds like it could be an actress.

Good on you. Finally. I'm proud of that one. Yeah, you should be. You have every right. Finally, this from Vicki Knorr in Louisville, Kentucky. Keen-eyed viewers can also see this effect, Bailey's Beads, simulated during the opening credits of Star Trek Voyager,

the opening title sequence for the old Star Trek series Voyager. I looked it up. Of course, this is available online. It's possible. It's possible that there might just be a flash of Bailey's Beads there. I won't guarantee it, but Vicki, why not? So we're ready for next time. Don't they call them holographic doctor beads?

No, no, no. He works for us. All right. The question for next time. What is the funny word that you're probably hearing tossed around, including on Planetary Society videos? What is the funny word used when three celestial bodies are lined up, like in an eclipse? Go to planetary.org slash radio contest. Is it stooges? Yes. Dang it, I need a new question.

No, not those three bodies. That are often lined up. Here is the quirk with this week's contest. Because of all of the big eclipse stuff getting in the way and the fact that I'm going to be headed off to Illinois, we are going to make the deadline for this two weeks off. In other words, Wednesday, August 30th at 8 a.m. Pacific time. So all of you who are always complaining

that you just don't have time to enter the contest, well, hopefully this time you do. Wednesday, August 30th at 8 a.m. And you might win yourself a 200-point itelescope.net account and one of those brand new and quite lovely Chop Shop designed planetary radio t-shirts. Okay, we are finished, I think. All right, everybody, go out there, look up the night sky or the appropriate day sky on eclipse day, and think about clear skies,

both literal and figurative. Thank you, and good night. Well done, Bruce. Have a good time up there. and figurative. Thank you, and good night. Well done, Bruce. Have a good time up there. Looking forward to getting dark with you. Let's get dark and peaceful. He's Bruce Betts, the Director of Science and Technology with What's Up, just before he heads for that zone, just as

I am. One last warning to everyone who hasn't yet experienced the Great American Eclipse on August 21st. Protect your eyesight. Make sure you only view the eclipse through certified glasses or other optics, or use a pinhole projector. Planetary.org slash eclipse has the lowdown.

I hope to see many of you at SIU Carbondale for Planetary Radio Live on Eclipse Eve, August 20th, and the next day in Saluki Stadium for a spectacular eclipse celebration. You can learn more at eclipse.siu.edu. Planetary Radio is produced by the Planetary Society in Pasadena, California, and is made possible by its blindingly brilliant members. Daniel Gunn is our associate producer. Josh Doyle composed our theme, which was arranged and performed by Peter Schlosser. I'm Matt Kaplan. Clear skies.