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IN A NEW LIGHT
JULY 11, 1996
TRANSCRIPT
Jeffrey Kaye of KCET-Los Angeles takes an up-close look at Jupiter's giant moon, Ganymede.
Click here for the RealAudio version of this discussion.
Check out the latest images from the Galileo Probe.
Keep track of the Galileo spacecraft.
JEFFREY KAYE: These are images of Ganymede, the largest moon in the solar system. They were taken June 27th by the spacecraft Galileo as it sped by just 519 miles from the Jupiter moon. The computer enhanced images were released today at the Jet Propulsion Laboratory in Pasadena.
TORRENCE JOHNSON, Galileo Project Scientist: Science response is just overwhelming. This thing is performing--
SPOKESMAN: Certainly beyond our expectations.
TORRENCE JOHNSON: Beyond our wildest dreams. When we saw some of the problems we had early on with this and, and thought about how we would do this Jupiter mission, I think many of us never imagined that we would be sitting here today with this, with this wealth of data. I mean, it's doing a beautiful job.
MR. KAYE: Project scientists use the data and images to offer a guided tour of Ganymede's landscape. The moon is pock-marked with craters and wrinkled with icy mountainous slopes. Scientists found evidence of unexpected earthquake activity and a magnetic field around the moon.
JIM HEAD, Brown University: Now that we take a look at this in more detail, we can actually see that he heavily-cratered region is old, and so it's completely reversed our thinking about the geological history of the planet. It's really turned our thinking upside down.
MR. KAYE: Ganymede is just one of at least sixteen moons that orbit Jupiter. It is composed largely of rock and ice. The Ganymede fly-by was just one of the missions planned for the two and a half ton Galileo orbiter. The spacecraft was launched in 1989 from the space shuttle Atlantis. En route to Jupiter, it looped twice around the Earth and once around Venus, using the gravity of those planets to boost its own energy. Despite various technical
setbacks, in December, Galileo was able to drop a companion capsule by parachute into Jupiter's atmosphere. That probe was packed with scientific instruments which sent back data on the largest planet in the solar system during a one-hour suicide descent. The information showed the planet to be extremely windy, gaseous, and surprisingly dry, and it led many scientists to rethink their theories about planetary formation. While the probe disintegrated, the spacecraft Galileo, which sent back today's pictures, went into orbit around Jupiter. Scientists expect it will keep orbiting for another 18 months, sending back streams of data and pictures of Jupiter and of moons first discovered by the scientist Galileo nearly 400 years ago.
MR. KAYE: Joining me now to discuss the spacecraft Galileo and its findings is Torrence Johnson, who is the Galileo project scientist. Dr. Johnson, welcome. Thanks for joining us. The pictures are dramatic, but what do the pictures tell us, or tell you, about Ganymede that you didn't already know?
TORRENCE JOHNSON, Galileo Project Scientist: (Pasadena) Our previous views of Ganymede were, if you will, kind of a long range reconnaissance of the Voyager Spacecraft in 1979. And they gave us views of the satellite that were sort of like a meteorological satellite view of the Earth.
MR. KAYE: Right.
TORRENCE JOHNSON: Now we're getting pictures that are more like land side views. These pictures cover an area only approximately the size of the Los Angeles Basin, and if there were a Rose Bowl there we could see it.
MR. KAYE: Right. But they are incredible. But what do you know by looking at the pictures, the details? One of the scientists said that it's reversing your thinking about the origin.
TORRENCE JOHNSON: We had a lot of theories built up about how to explain what we saw in the Voyager pictures. Some of those look okay. Some of them don't, in particular, ideas about how young or old various surfaces are.
MR. KAYE: Right.
TORRENCE JOHNSON: We thought that some areas were rather smooth and maybe covered with young material. We look at these pictures, we see these things are covered with little meteor craters. That means to a space geologist that those--that surface has been there being hit by things for a long time. And so we're having to actually turn over some of the ideas of which thing's younger than the other on the surface already.
MR. KAYE: One of the things you've been saying for a long time about this whole process, this Jupiter process, is it's going to help you understand the formation of the planets, maybe even our own planet. Is it helping? Is there a use for this information, or is just good, solid information?
TORRENCE JOHNSON: Well, it's certainly good, solid information. The use for this information will come in understanding how planets tick. I mean, what we're learning here is things about fundamental geology and geophysics, except not on a world like ours, on literally a glacier world, a frozen world, where ice acts like rock. So, in effect, it's a natural laboratory for trying out some of these ideas that we have been applying to our own Earth, you know, how plate tectonics works, how that type of thing works.
MR. KAYE: But if this world is so much different from ours, how do you then apply it to our world?
TORRENCE JOHNSON: Ah, a scientist always likes to apply their theories outside the place where you know they work. If you're going to get a better theory, you have to change the conditions of the experiment, and here nation's changed the conditions of the experiment, substitute ice for rock, change the temperature, put it around Jupiter, put in a radiation field, so the next generation in the view of scientists that will study the Earth will be better trained and with better theories as a result of trying to explain these things.
MR. KAYE: Interesting. Let's talk about how you're able to do this. We mentioned before that there were technical glitches. One scientist said today that because of them he had to do a complete brain transplant on a computer 400 million miles away. Why did you have to do it, and how did you do it?
TORRENCE JOHNSON: Well, the biggest problem we've had with the spacecraft since launch was that the main communication antenna, which is sort of an umbrella-like device, did not open up completely as we expected it. So it's not a dish, it's not a good antenna at all. Fortunately, we had a smaller antenna from which we can communicate more slowly but which is working just fine. And what we had to do is reprogram the software on board. What we had to do was change the operating system. Anybody who's loaded Windows 95 knows what I'm talking about.
MR. KAYE: Right.
TORRENCE JOHNSON: Change the operating system to make this--
MR. KAYE: Reprogram the computers.
TORRENCE JOHNSON: Reprogram the computer to allow us to take the bits on the spacecraft computer and analyze the data on the--on the spacecraft and send down some of the answers, rather than send down all of the data. It's a bit like what happens when you pull a picture off the World Wide Web these days. That picture has been data compressed. And we're using very similar techniques.
MR. KAYE: Now, this is also going to help you, these techniques, for future explorations, right, in terms of programming the computers of future spacecraft?
TORRENCE JOHNSON: Yes. This was the first spacecraft that we've flown that really used microprocessor technologies, old by the standards of what's on your desk now.
MR. KAYE: Right.
TORRENCE JOHNSON: But it was the first one. It gives us tremendous flexibility. And we're routinely building in that type of flexibility in the next generation of spacecraft.
MR. KAYE: Flexibility to do what, for example?
TORRENCE JOHNSON: To reprogram, to get around problems, to take advantage of the unknown. When you send these things out there, you're going there because you don't know what you expect to find. You have to be able to react to it.
MR. KAYE: What's been the most exciting and perhaps the most unexpected finding for you?
TORRENCE JOHNSON: Actually, it wasn't one of the pictures this time. The most unexpected finding for me as a scientist was that Ganymede may have a magnetic field. We really hadn't expected that satellite or moon to have a magnetic field. It's cold, made out of ice mostly with rock in its center, and yet, when we flew by, two of our instruments clearly saw an indication that it had a magnetic field.
MR. KAYE: Why is that a big deal?
TORRENCE JOHNSON: Umm, well, again, magnetic fields exist on some planets but not others. We don't know too much about exactly how planetary magnetic fields are formed, even our own Earth. We have theories. We wouldn't have expected from some of those theories to find a magnetic field around Ganymede. So if this really holds up it may change some of our ideas about how planetary magnetic fields are formed. And that, in turn, tells you about the interior planets. It's a way of probing inside, below the surface that you can see.
MR. KAYE: You're talking about planets, but this is not a planet. It's a moon.
TORRENCE JOHNSON: It's a moon but it's about 1/3 the size of the Earth. It's bigger than the planet Mercury, and so it's a planetary process.
MR. KAYE: Uh-huh. You've been with us for a long time. How did it make you feel when you saw those pictures coming back?
TORRENCE JOHNSON: Frankly, tremendous relief.
MR. KAYE: Relief.
TORRENCE JOHNSON: After so many, so many problems getting here and just at the last minute getting all of this new software loaded, during the entire week of the encounter where you're on kind of pins and needles, is everything really going to work, and we saw those first lines of those pictures come in to--wow, it worked, and the data are fantastic.
MR. KAYE: What's next for Galileo?
TORRENCE JOHNSON: Well, we got to get the rest of the data off the tape recorder. And the way we operate this mission is we load up our tape recorder on board the spacecraft and then read the data back during the rest of the orbit, so we have a lot of data to read back in this orbit and then we encounter Ganymede again in September.
MR. KAYE: What are you hoping to find with the rest of the data that's coming back?
TORRENCE JOHNSON: We'll be studying the great red spot of Jupiter, so we starting working on Jupiter's atmosphere. We'll get more data about the magnetic field of Ganymede. We have lots more pictures and also compositional maps of the surface, information about a possible atmosphere on Ganymede.
MR. KAYE: Great. Well, thank you very much for joining us. Good luck.
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