Voyagers 1 & 2, 1979-1989, Page 2
It was Voyager that sucked me in [to planetary science], and I asked to work with somebody on Voyager data of the moons of Jupiter. Bob Strom was my advisor. In those days, the tools were pretty primitive, and in fact we were all gearing up to count craters on the satellites there, with rulers.
Of course the Voyager cameras were digital in a certain sense, so numbers came out, but my job was to take the print-outs of the numbers, pixel by pixel—I’m really not kidding you—and hand-draw contours through those pixels to show where the different brightness levels were. We didn’t really even have the ability to turn those numbers into a grayscale image, or if we did we couldn’t work with them numerically. So I really did transfer those numbers to pieces of graph paper and pixel by pixel draw the contours.
If you go to the Satellites of Jupiter book, published by U of A Press, for each one of the nine volcanoes that were detected erupting above the surface of Io there’s one of my hand-drawn plume contour maps. I wrote a few computer programs that would lob off particles in different directions at different speeds, and the goal was to match those contour plots.
In those days the Jet Propulsion Lab was a lot more open than it is nowadays. I think it was that summer that the Voyager 2 spacecraft flew by Jupiter, we loaded a bunch of people into my family station wagon that I had inherited and we drove to California, and a bunch of us just got to go hang out at JPL with our jaws hanging down looking at these amazing pictures coming back. As students we could all go there as spectators of this amazing encounter, and for the later Voyager encounters I got to go back as a productive graduate student, ruler in hand, measuring the sizes of these geological features that we scarcely understood.
I was very thrilled my first semester at LPL to be able to see the Voyager 1 Saturn encounter, which was in November, and see all the images coming down from that with Bob Strom, who was on the imaging team. I did some work counting craters on the Voyager images of the Saturnian satellites and determining size-frequency distributions for the craters to determine the different impact populations pretty early on with him.
So I was at JPL when the Voyager pictures were coming back from Saturn and Uranus and Neptune, and we were seeing those close-up images of Enceladus or Miranda, or—this was after my LPL time, but when we got to Neptune, those pictures of Triton—so many of those blew me away. Those are incredible memories of seeing new worlds for the first time.
Then there were the moments when something clicked scientifically. I remember the first time that happened—one of the things I did for my dissertation was looking at the temperature measurements of the Galilean satellites made by Voyager during its flyby in 1979—just poking through the data and suddenly realizing, as I plotted points on this Hewlett-Packard pen plotter that we had back then, that the patterns of thermal emissions are totally different between Ganymede and Callisto. Nobody ever knew that before, and here it was appearing before my eyes.
The very first mission I got involved in when I got to LPL was again courtesy of Don Hunten and his colleague Lyle Broadfoot, and Lyle invited me to be a team member on his ultraviolet spectrometer instrument on Voyager 2, which had one more flyby to go, and that was in 1989, and that was the flyby of Neptune. This was long after Voyager was launched. That group was inherited from LPL from the University of Southern California, in fact, so it doesn’t count as being an LPL success from the beginning. But it was a great inheritance.
Lyle was very nice; he said, “Why don’t you help us with Triton?”
So in ’89 I got to go to JPL [Jet Propulsion Laboratory], and I was there for the flyby. The ultraviolet data were neat but I snuck over to the imaging room so I could see the very first pictures of Triton, so I was among the set of human eyes to first lay sight upon this world, which is the most distant moon in the solar system excluding Pluto and Charon—this moon of Neptune called Triton.
One of the most memorable things to me was the 1989 encounter of Voyager 2 with Neptune, including Triton. This was just pure exploration. Neptune and the satellites went from just points of light in the sky—in fact, some of the satellites were discovered by Voyager so they weren’t even that—to worlds where we had high-resolution images, overnight. Literally, overnight, it just came in, in the wee hours of the morning.
We processed the images, and at Jet Propulsion Laboratory television news crew trucks were lining the street on out of the laboratory. We had the wee hours of the morning to process the images before the press conference the next day, showing the world brand-new stuff. It was really something.
One of the high points was flying by Neptune’s satellite Triton. Really an exciting time. We did an experiment where we watched the Sun set behind Triton. It’s called an occultation experiment—you’re measuring the transmission of the atmosphere by seeing how the spectrum changes as the Sun moves behind the planet. The light passing through the atmosphere is absorbed and the shape of the absorption spectrum tells you what the composition of the atmosphere is and how it’s distributed in space, and you can get the temperature.
I was looking at the data and I realized at that moment I was the only person in the world that knew what the major constituent of the atmosphere of Triton was. Wow. But then I blabbed it, so that only lasted for about five minutes.