IRA FLATOW: This is Science Friday. I’m Ira Flatow. When you think of NASA’s Voyager Mission, you may first think of The Golden Record. Do you remember that phonograph recording being carried to tell alien agencies who and where we are? Or you may think of the 1990 portrait Voyager 1 shot of our entire solar system in which Carl Sagan famously opined, “On that blue dot, that’s where everyone you know, and everyone you ever heard of, and every human being who ever lived out their lives. It’s a very small stage in a great cosmic arena.”

But Voyager also brought us the first close-up views of Uranus and Neptune, showed us spoke features in the rings of Saturn, and details of Jupiter’s storm that we had never seen before and never imagined. Voyager imaged EO’s volcanic plumes, the potential for life on Enceladus and Titan, and Voyager is turning 40 this year. Yeah, and there are actually two Voyager spacecraft– Voyager 2, launched on August 20th, 1977, Voyager 1 closely behind it on September 5. And Voyager one is the most distant manmade object from Earth, 8-track tape recorder on it and all. Here to look back with us on four decades is Carolyn Porco, planetary scientist, former member of the Voyager imaging team. She joins us a number– she’s been on our show a number of times. Welcome to Science Friday. Welcome back.

CAROLYN PORCO: Thanks for having me. Thanks for having me.

IRA FLATOW: You’re welcome. I have to say for starters that I can’t believe we got everything we did from Voyager, and those crafts that are recording 8-track tape. Doesn’t it blow your mind?

CAROLYN PORCO: Yes, it does blow my mind. And for me, the best thing about this anniversary, and the celebration that everyone seems to be making of it, is just to have the opportunity to spend some time remembering what we all accomplished so long ago with so very little.

IRA FLATOW: Well, let’s talk about that. Set the scene for us. What did we know about the outer planets at that time when Voyager was conceived and launched, and what did we learn?

CAROLYN PORCO: Well, we knew, as I just said, we knew very little, and that’s what’s just so remarkable to me to remember. We even knew very little about Jupiter and Saturn. I mean, we, you know, didn’t know how they were structured. Rotation rates, at least for Saturn, were not clear. Composition was an entirely different matter. We knew nothing about what we were eventually going to find in the rings of Saturn.

And then as far as Uranus and Neptune go, that was the hinterlands. Even in the most powerful telescopes on the earth they were just these fuzzy little dots, or at most a little little blob of blue. And not much was known.

Maybe we knew a moon or two, so it was really venturing into uncharted territories. And this is what is so monumental about what Voyager did. Most of the solar system, and it doesn’t matter how you measure it– if you count the number of bodies, or you measure the amount of mass that is contained in those bodies– most of our solar system, the vast majority of it, exists beyond the orbits of the asteroids.

And where we live, the Earth, along with Venus, and Mars, and Mercury, our neighbors, there’s virtually nothing here. We’re nestled in close to the sun, but our solar system exists out there, and we could not have claimed to know what our own solar system was like until we had a mission that toured the outer solar system in the way that Voyager did. And so it opened up– it blew the doors off the house– the view of our solar system for our investigation and understanding.

IRA FLATOW: There are so many little side stories about this mission, and I want you to tell us one of the original science stories, which is that it almost didn’t get funding to go as far as it went, did it?

CAROLYN PORCO: Oh, now, and it’s a wonderful side story because it’s got a little bit of subversion in it which, I don’t know, appeals to my subversive spirit maybe. But the funding was only provided to go to Jupiter and Saturn, but the engineers kind of winked at each other and said, oh yeah? We’ll show them. And they designed it so that, if given an extension, the mission could go to Uranus and Neptune. So whenever there was a decision to be made– are we go going to build this instrument with the capability to last up until Saturn encounter, or are we going to give it the extra, you know, whatever it needs in order to last as far as Neptune? Well, they chose the latter. And of course, we are all the very, very much better for it.

IRA FLATOW: You know, I followed this mission closely. I remember being at JPL when it flew by the rings of Saturn. I think it was a Saturday night, I remember, about midnight, and I remember there was something wrong with one of the arms on it at the time. There was a little hiccup on it.

But we knew almost nothing about those rings when we first launched Voyager, and I remember the amazing amount of new information, the stunning close-ups, the spokes, the little maybe moons in the rings, just amazing stuff that we learned about Saturn’s rings.

CAROLYN PORCO: Oh, Saturn’s rings were the star– well, one of the stars– of the Saturn encounter, because that was– I mean, whoa. Just being confronted with that and seeing all the complexity in the rings was so mind blowing. And I was lucky because it was so many new discoveries in the rings that two very important topics fell to me, a graduate student, to work on for my doctoral dissertation. And that kind of defined what I would do for the rest of my life because I ended up studying the very type of rings that were found in the late ’70s in circling Uranus.

So when Saturn encounter was over, when I finished my PhD thesis, I was added officially to the Voyager imaging team to help plan the Uranus and Neptune encounters because I had the domain knowledge that was required for studying Uranian rings. So the Saturnian ring system– I have a very soft spot in my heart for it. But then, of course, there was Titan, which was a big– just such an interesting body. And we never got to see the surface of Titan, like we had hoped, with Voyager, and that was left for Cassini to do.

IRA FLATOW: And of course, how do you how do you decide which moons of all those the gas giants to look at? How do you know which ones to choose?

CAROLYN PORCO: Well remember, when we first got there with Voyager 1, we didn’t know about all the moons. We only knew about, you know, a handful of them, and the important targets for the Voyager 1 fly-by were the rings, the atmosphere of course of course, the globe of Saturn itself– that’s always the case– but the other targets would be Titan. As I just said, was a major great anticipation about what we would find on Titan and then the rings.

And then, since the Voyager 1 mission was successful, what they decided to do with Voyager 2 is pay more attention to the other moons, the other major moons, and they found others in the process. And especially Uranus and Neptune, it’s very hard to see the moons, especially when it’s even challenging to see the planet itself. We found lots of moons, so you know, I mean, I could go into lots of detail about how Voyager– their programming of it got to be so sophisticated that we were able to plan ahead, leave a space in our imaging sequences, leave an empty space so that when we got there, if there was a new moon, and we had a target to it, we’d have the opportunity to do it. Things like that happened.

IRA FLATOW: And of course that sort of set the stage for us realizing that the moons out there could be as important to explore as any of the planets because they might harbor life in them.

CAROLYN PORCO: Yes, well they certainly– we found that they could harbor oceans, and then subsequent missions like Galileo at Jupiter, and of course Cassini at Saturn, found that there are moons around each body, each planet, that do have subsurface oceans. I mean, we know for sure they have subsurface oceans now. And with Enceladus, the small moon that has a subsurface ocean at Saturn, we even know that it has all the basic ingredients for what we call in our business a habitable zone.

It checks all the boxes for a body of water that we want to go back to and investigate further because it could– we’re not saying it does– but it could possibly harbor life. So it has– I mean, again, our explorations of our solar system have really not only put– they’ve given us a perspective on ourselves and our cosmic place, but they have shown us how limited our thinking is until we go traveling. You know, Rudyard Kipling, I believe, was the one who said travel can be mind expanding, and our explorations of our solar system have certainly shown that to be the case.

IRA FLATOW: And so which moon would you like to go back to if you could just wave your magic wand?

CAROLYN PORCO: Oh, I would go back to Enceladus. I made a big deal over the last 10 years, since we have found the geysering basin at the South Pole, that Cassini has flown through, and we’ve grab samples of this material, and we’ve analyzed, and we know it has organic compounds. It’s coming from an ocean, a salty ocean, with salinity comparable to our Earth’s oceans. It has simple organic compounds, even evidence for hydrothermal activity on the sea floor. I mean it’s got everything you could possibly want at this point in time to make a decision about what’s the best place to go. We now know Enceladus is the best place to go.

IRA FLATOW: So are we going?

CAROLYN PORCO: Well, there are two groups that have proposals that they have submitted to NASA for NASA’s New Frontiers program. That should be decided by the end of this year. That’s two proposals to Enceladus out of 12, so it’s not clear at all that those proposals will be selected. But in fact, you’ve given me the opportunity to say that there’s a documentary that had aired and will air again on September 13, I believe it is, at 10:00 p.m. on PBS. It’s called The Farthest, and it celebrates what Voyager accomplished. But immediately after that, there’s a mini documentary called Second Genesis, and I am the subject and the guide in this documentary, and I go through– it’s kind of about my quest to go back to Enceladus to search for life. So I hope everybody watches that.

IRA FLATOW: So you’re sort of the new Carl Sagan.

CAROLYN PORCO: Oh, I think there’s many that probably would qualify for that, but I appreciate the compliment.

IRA FLATOW: So is there still a mission left for the Voyager spacecraft. I mean, are they going to run out of fuel? How far can they go? What do they do out there now?

CAROLYN PORCO: Well, you know, in my mind the Voyager mission is the Apollo 11 of the planetary exploration program. It has earned that stature, that iconic stature, in our culture, because not only, as I just said, did it open up the solar system for our view, but it carried with it a record of human greetings, and songs, and pictures of our planet that constitute a message from humanity to the Milky Way, to whatever, whoever, finds Voyager, if ever. They will know, by looking at not only the construction of the spacecraft, but this record, that there was an intelligent civilization that put this together, and sent it on its way, and it was sent across space into the future. And it will very likely live for billions of years.

It could do that. Certainly the Voyager record could do that. And in some sense, it is the closest that we, humanity, will ever come to immortality, and people immediately registered with that. You know, it moved people. It stirred people in such a way that Voyager has become such a– people have such a fond feeling for this mission.

And in August of 2012, it finally, Voyager 1, entered interstellar space, and so Voyager defined us. It defined us as an interplanetary species during the 1980s, and now it has defined as an interstellar species. And so it will continue. That will be its mission.

In about 10 years, between 2 and 10 years, depending how the power on the spacecraft is managed– it could last another 10 years, and then it will wink off. It will have no more power to send us any signals. It will be an enormously sad moment in history when that happens, but Voyager will continue long long after– it could be long after humanity is gone. And here’s another crazy thought that one of the producers of the Voyager record, in fact, brought up. His name is Timothy Ferris. Perhaps billions of years from now, Voyager could be found. The record might be found, and it could be found by a civilization that hasn’t even evolved yet. So we have touched– it’s like knocking on eternity’s door. That’s what Voyager has done for us.

IRA FLATOW: Carolyn Porco is my guest this hour on Science Friday from PRI, Public Radio International. Well that that’s just, you know– and it’s still functioning out there in interstellar space, sending stuff back? How long does it take the signal– it’s like an 8 watt transmitter or something, isn’t it? I mean, how long does it take the signal to get there? Can we still hear it?

CAROLYN PORCO: I think by the time– I just read myself– it gets to us, it’s some 16 trillion [INAUDIBLE] watts, so you know, they’re listening very closely. Let’s put it that way. But it’s something like 16 or 17 hours of light travel time, meaning light, the fastest thing that we know, and as far as we know the fastest thing possible, takes 16 or 17 hours to get to us from Voyager. It’s very far away and increasing.

IRA FLATOW: But you know, you make it a good point about it entering our psyche and our culture. I mean, even one of the Star Trek movies had it as a gotcha at the end of the movie, if you remember.

CAROLYN PORCO: I remember that so well. And I remember when it got to the end, and I realized anyway [? Viji ?] was actually the Voyager spacecraft. I just– I think I was jumping up and down I was so happy.

IRA FLATOW: And we don’t make them like this anymore, do we?

CAROLYN PORCO: Oh, no no. That’s not true. We do make them. We make them pretty good.

Cassini has been a monumental mission. It’s technologically so much more advanced over what Voyager was.

IRA FLATOW: But Cassini’s the last one, isn’t it, of that kind of spacecraft?

CAROLYN PORCO: Cassini is the mission that we put in orbit around Saturn. And I don’t know when we’ll see a mission that’s that huge again. It carried 12 instruments, and it also carried a probe that was deployed to enter the Titan atmosphere and land on its surface. That was landfall in the outer solar system. Cassini has accomplished so much, and we are about to bid that spacecraft goodbye, too. September 15 Cassini will be sent into Saturn, and a 27-year mission– 20 years in flight and 13 plus years at Saturn– will come to an end.

IRA FLATOW: Well, we’ll be saying goodbye to that also. You know, it is emotional. It’s an emotional–

CAROLYN PORCO: It is, especially if you’ve been involved, and you’ve devoted your life to missions like this. It’s really, for me, kind of the end of my career as a planetary explorer. I’ll be involved in other missions in a small way, but I’ll never take on the kind of job that I’ve had on these two. And I’m so proud of what we’ve all done, and I feel like I’ve led a charmed existence.

IRA FLATOW: Well, we thank you for all these years that you’ve joined us to talk about Voyager, Cassini. And we wish you, you know, finding interesting new stuff to work on. Carolyn Porco, thank you very much.

CAROLYN PORCO: Thank you. Thank you.

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