365daysDate: August 26, 2009

Title: 20th Anniversary of Voyager 2 at Neptune


Podcaster: Martin Ratcliffe and Dr. Ed Stone

Organization: None

Description: In August 1989, the Voyager 2 spacecraft performed the first reconnaissance with the solar system’s outermost major planet, Neptune. Now, 20 years later, the Voyager mission Project Scientist, Dr. Ed Stone, joined me for an interview reliving some of those momentous events of that remarkable week of discovery in August 1989, and we hear about the impact Voyager had on future planetary missions. Voyager 2’s final encounter was a remarkable moment in history, marking the end of humanity’s first survey of the solar system. Mission control at the Jet Propulsion Laboratory in Pasadena, California, was packed by the world’s press and the world’s top planetary scientists. The exciting results from that mission, including Neptune’s large dark spot, fast moving white clouds, and a remarkably active surface of Neptune’s moon, Triton, are now well known. Voyager’s mission helped define future orbital missions to the outer planets.

Bio: Martin Ratcliffe is Director of Professional Development for Sky-Skan, a leading digital planetarium manufacturer. He received a BSc in Astronomy from the University College London, England. Martin has published 4 books, including The Night Sky Revealed (Barnes and Noble) and State of the Universe 2008 (Praxis-Springer). While his final year research project on Sco X-1 produced a published paper, Martin pursued a career in planetariums, working at theaters in Armagh, Northern Ireland, Buhl Planetarium in Pittsburgh and the CyberDome Theater in Wichita, Kansas. A former President of the International Planetarium Society, Martin is a contributing Editor for Astronomy magazine, co-writing the Sky Show monthly column for the past 13 years.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Riley, Drew and Brady Collins.


Hello, I’m MR, of Sky-Skan, and a contributing editor to Astronomy Magazine. In June, while attending the American Astronomical Society meeting in Pasadena, California, I recalled my first visit 20 years ago this month when I was at the Jet Propulsion Lab covering humanity’s first encounter with Neptune by the venerable Voyager 2 spacecraft in August 1989. On August 24, Voyager flew 3,000 miles above the north pole of Neptune. Five hours later, in the middle of a sleepless, exhausting, and special night on August 25, Voyager 2 passed 25,000 miles from Triton, Neptune’s largest moon. The Triton images made the lead story in the August 26 issue of the Los Angeles Times, which exclaimed “Cold world of ice-spewing volcanoes and quakes revealed in photographs.”

I took the opportunity of being in Pasadena to speak with Dr. Ed Stone, Project Scientist of the Voyager missions, and here is the recorded interview.

MR: We’re getting close to the 20th anniversary, or this is the 20th anniversary of Voyager 2 at Neptune. We’re talking to Dr. Ed Stone who was Project Scientist of the Voyager mission, then later you were the JPL Director after that, so give me your perspective from a 20-year vantage point.

Dr. Ed Stone: Well, Voyager really changed our view of the Solar System. It really revealed how little we actually understood our neighboring planetary and satellite systems, and how diverse they are. I think, in one sense, that was the most important thing we learned, and that is that nature is incredibly diverse, even though these objects, many started out looking very much the same initially, today, they have evolved and are very distinctive objects.

MR: So, to me the exciting thing about this mission was that this was the first time we would visit the major outer planet of the solar system (don’t want to start arguments about Pluto) but it’s in the place of the Solar System – the last major planet that humanity get’s its first look. Can you talk about that?

Dr. Ed Stone: Well Neptune, of course, is the outermost planet in the Solar System, where the sunlight is only 1/900th in terms of energy, and yet we found the Great Dark Spot in its atmosphere, we found that the moon Triton has geysers erupting from its icy surface, even though it’s only 40 degrees above Absolute Zero, so even the most remote objects still has processes which contribute to the continuing evolution of the bodies in that remote part of our Solar System.

MR: One of the interesting things I thought about we could talk about: at that encounter, where the world’s press gathered in the forecourt of JPL, we were all in our little caravan huts, and we were watching the images as they came in on the television screens, and then to get the image releases every day, they would be printed out, and if you were lucky you got copies of the color images: this was pre-internet, we had email, but nowadays raw images come down from the Mars rovers, and people can access those almost instantly. Give your perspective of perhaps how Voyager was probably one of the last missions that did that kind of image release, and that now we’re in a different environment, but a lot of listeners would not appreciate how things were.

Dr. Ed Stone: In those days, of course, we did not have the internet where one could immediately release all these images, and the flyby events were “events” that were in fact world wide, and we did manage, by the time of the Neptune encounter, in realtime to provide the images not only to JPL but to also to planetaria around the country, and the Triton encounter was actually in the middle of the night, and people were in line waiting to participate in the sense of discovery, in seeing something no one had seen before, and realizing, recognizing again, how different it was than anything we’d seen before. So there really was a sense of community of exploration of the moment, which was possible. What’s happened today, of course, now that that has become even more the case with the world wide web. When the Mars Sojourner rover first landed on Mars back in 1997, hundreds of millions of logons were evidence that in fact this was a new stage of exploration, even beyond what we could do with Voyager, but Voyager really set the stage with trying to make it possible for as many people as possible in those days to participate in the sense of discovery.

MR: That, for me, was one of the first kind of planetarium events, because we phoned back stuff (to Armagh Planetarium,) I was living in Northern Ireland then, and since then I’ve done lots of events like the Triton landing, and covered the Mars landings for large audiences.

Can you tell me a little bit about the earlier history of the challenges of getting Voyager first off the ground, maybe even funded, past Jupiter, and then the decision at Saturn to go for Uranus and Neptune, and bypass Titan around Saturn on the second time because you got Voyager 1 there first?

Dr. Ed Stone: Well, of course this was the opportunity to flyby all four giant outer planets, called The Grand Tour, it occurs only once in 176 years, and 1977 was the year. We could have done it in ’76 or ’78, but other than that it would be 176 years more. So there was, in fact, initially a very ambitious plan to fly a spacecraft, with a high probability to make the 12-year journey to Neptune, but that turned out to be too expensive in an era where there was Viking (Mars landers) and the beginning of the Hubble Space Telescope, it was decided to cancel this opportunity.

Rather than that, the engineers at JPL came up with a more modest spacecraft, which is what Voyager is, a four year mission just to Saturn. So we began a new mission called Mariner-Jupiter-Saturn ’77, with just the objective of a four year flight to Saturn, but cleverly we made it possible for an option to be selected that if Voyager 1 succeeded in doing the prime Saturn science, we could then target Voyager 2’s flyby of Saturn and not to optimize Saturn, but to be able to go on to Uranus and Neptune. So in December of 1980, when Voyager 1 had successfully flown by Saturn, NASA decided we should stay in the plane of the planets, to continue on to Uranus, and then eventually Neptune, and now of course, along with Voyager 1, leaving the entire solar system.

MR: So give me a few thoughts first about Triton night. I remember standing in the press room and (scientist) Rich Terrille was standing next to a few of us with the TV. We had the wide angle images coming in, we had little strange looking streaks on the surface, and then all of a sudden there was a high resolution, narrow angle image of Triton. Your thoughts?

Dr. Ed Stone: It was, again, just remarkable. We had — this was ten years after Jupiter — where we had seen things we had not expected like volcanoes on Io, and cracked ice on the surface of Europa, and here the last place we visited in the Solar System, the coldest place we visited, also was incredibly different than we expected, and that we had seen anywhere else. Each of these bodies was unique, and so here was a small little icy world with evidence of past tectonic activity on its surface, with a ice polar cap of frozen nitrogen ice, and with streaks which in fact are the deposit of geysers erupting from that cold icy surface.

MR: Yeah, they were amazing. Give me a perspective of where Voyager is now, and what is still happening with the mission.

Dr. Ed Stone: Well, the Sun creates a bubble around itself, it has a million mile per hour solar wind, blowing radially outward creating this bubble called the heliosphere. Outside the bubble is interstellar space, material from other stars. When we were launched, and we had no idea how big this bubble was, but we now know that in fact in another five or six years, Voyager 1, which is now 110 times as far from the Sun as the earth, will actually be in interstellar space. Both spacecraft are now in the final outer layer of this bubble called the heliosheath, which is where the supersonic wind from the Sun has slowed down in a shock, and is turning around to flow down the tail, because the heliosphere is a comet-shaped object. And this is a totally new region, no spacecraft has ever been there before. It’s a very important region where material from other stars begins to interact with material from our own Sun. And once we cross the boundary of this bubble we will then me immersed for the first time in material from all other stars that exploded nearby a few million years ago.

MR: So a last question, how did the Voyager project as a whole, and later you became Director of JPL, how did the experience with Voyager impact the future Solar System missions that occurred in the late 90’s and now in the 21st century?

Dr. Ed Stone: Voyager, of course, revealed the complexity of the objects and really set the stage then for the return to Jupiter by Galileo, which orbited Jupiter and therefore could fly much closer to the moons of Jupiter than Voyager could, and then drop a probe into the atmosphere of Jupiter.

It also set the stage for another mission that’s being worked on now called Juno, which will be launched in 2011, which is going into a polar obit around Jupiter so it cane measure more carefully the gravitational and magnetic field of Jupiter to help understand the interior processes that occur in that giant planet which is all liquid, so it’s essentially a gas and liquid planet.

Voyager also set the stage for the Cassini mission which is now in orbit around Saturn, it’s flying by Titan every other month, and is revealing the complexity of that world where we believe now that methane, natural gas, is raining on the surface, creating lakes of natural gas which are shown now occurring in the polar regions of that world, as well as finding geysers erupting from a moon called Enceladus.

Voyager also set the stage for future missions to Uranus and Neptune, although none are yet scheduled.

MR: Well, thank you very much for joining us on 356 Days of Astronomy, an exciting podcast I think for everyone to reflect on the Voyager 2 encounter with Neptune, 20 years ago in August 1989. Thank you, Ed Stone.

Dr. Ed Stone: Thank you, it’s been a pleasure.

End of podcast:

365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the New Media Working Group of the International Year of Astronomy 2009. Audio post-production by Preston Gibson. Bandwidth donated by and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at or email us at Until tomorrow…goodbye.

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