JANUARY 23, 1996
When the Galileo probe entered the atmosphere of Jupiter in December, it returned a huge volume of information that confirmed and denied a number of beliefs about the largest planet in our solar system. Jeffrey Kaye discusses the findings with NASA scientist, Dr. Richard Young.
JEFFREY KAYE: For 58 minutes last month, a space capsule packed with scientific instruments penetrated the atmosphere of Jupiter, looking for data on water, temperature, and chemical elements that scientists could only guess at before. The measures sent back to Earth have many scientists reevaluating their assumptions about how Jupiter and the solar system were formed.
WILLIAM O'NEIL, Galileo Project Manager: The probe performed a marvelous succ-- marvelously successful mission at Jupiter, providing our first ever direct measurements of an outer planet atmosphere.
JEFFREY KAYE: At a press conference, scientists discussed some of their findings. The release of information had been delayed because of the government shutdown. The capsule, which recorded the data, was launched last July from the spacecraft Galileo, which is now in orbit around Jupiter. It descended by a parachute, reaching speeds up to 106,000 miles an hour. As it plunged, it turned up information that surprised and puzzled scientists. Among its findings was an intense radiation belt researchers hadn't expected. There was also less lightning than anticipated, and stronger winds, up to 330 miles an hour. The largest planet in our solar system appears to be much drier than anticipated. There was no evidence of any significant water clouds, to the surprise of researchers. They surmised that Jupiter has an internal heat source, something they hadn't known about before. The team of about 50 scientists from around the world has been analyzing the data and promises more in the months to come. The scientist in charge of the Galileo probe is NASA's Dr. Richard Young.
JEFFREY KAYE: Dr. Young, thank you very much for joining us.
DR. RICHARD YOUNG: It's my pleasure.
JEFFREY KAYE: It sounds as if what you got back from the Galileo probe was a big surprise all the way around.
DR. RICHARD YOUNG: There were a lot of surprises. Basically, the thing that we wanted to go to Jupiter for was to understand the composition because we thought it could tell us important things about the way all the planets formed. And we found that some things were more or less what we expected but other things were quite different, and that's probably going to have--cause us to have to reevaluate some of the ways that we think about the way the planets form.
JEFFREY KAYE: We'll come to that in a minute, but what were some of the big surprises for you?
DR. RICHARD YOUNG: Well, the big surprises for me were based on previous spacecraft data, we expected to find a certain amount of water at Jupiter. The Voyager spacecraft, which flew by Jupiter in 1979, the analysis of that data that we'd obtained from those fly-bys, which is remote sensing, indicated that we would find about roughly two times or more the amount of water on Jupiter that we had expected to find based on the composition of the sun. We expect Jupiter to have basically the same composition as the sun.
JEFFREY KAYE: So the planet is drier than you'd expect?
DR. RICHARD YOUNG: A little bit drier than expected.
JEFFREY KAYE: It's much winder than you expected.
DR. RICHARD YOUNG: It is much windier than we expected, and that's an important finding because the meteorology of Jupiter has always been one of the major science goals for Galileo. If you look at a picture of Jupiter, you see this banded structure, these alternating regions of light and dark that run basically East-West. Associated with that banded structure is a system of winds that blows East-West on Jupiter. At the equator, they're blowing in the same direction as Jupiter rotates, and from cloud-tracking features with Voyager and from the ground, we measured winds of about 200 miles an hour. The probe encountered winds of over 300 miles an hour, and these winds extended well below the visible cloud tops that we could see. That's a very significant finding because it says that the energy source that's available to drive these winds probably comes from the deep interior of Jupiter. It's not due to sunlight. Sunlight is what drives the winds on the Earth. It's not probably what drives the winds on Jupiter.
JEFFREY KAYE: Other findings. You found a radiation belt that you didn't expect to find.
DR. RICHARD YOUNG: We found an inner radiation belt very close to the planet that we did not expect to find. It was a totally new discovery. It's in a region where we had never sampled before by any previous spacecraft. Let me explain what I mean by radiation belt. It's analogous to the Van Allen radiation belts that we know we have on the Earth. And it's a system of protons and electrons that are trapped in the planetary magnetic field, and they basically might grate along the planetary magnetic field lines from North to South, and that's what we have on the Earth. In the case of Jupiter, these radiation belts are about 10 times more energetic than they are for the Earth. And, in fact, we have to avoid them with the spacecraft because they will fry the electronics, and so the probe was coming in so fast that we could fly through them, the exposure time was small, so we could make the measurements and still get through them safely.
JEFFREY KAYE: Another finding was it was less cloudy than you expected.
DR. RICHARD YOUNG: It was less cloudy, and there sort of lies a little bit of a, of a troublesome problem. We went into a region that might have been somewhat anomalous with regard to clouds on Jupiter. When you take a picture of Jupiter, you see what are called these five micron hot spots. And basically what that means is that there are holes in the clouds and radiation can escape from deeper in the atmosphere of Jupiter than it can when you see a cloudy region. When you look at a cloudy region, you're seeing the radiation that Jupiter emits in the form of infrared radiation coming from the clouds. In these holes you're seeing radiation emitted deeper in the atmosphere. Those are relatively cloud-free. We may have gotten in right at the boundary of one of these relatively cloud-free regions.
JEFFREY KAYE: So that may or may not be typical of the rest of the planet.
DR. RICHARD YOUNG: It may or may not be. We're going to have to do more analyses. And these is where the Orbiter will come in, you know, very handy, because the Orbiter we can keep viewing the probe entry site, taking pictures, and also viewing the rest of Jupiter, so we can place the probe measures in a global context, so the data we're going to get from the Orbiter is still very important for understanding the probe results.
JEFFREY KAYE: What does it mean to you now as a scientist if most of the stuff you'd expected to find just wasn't there, you have to toss out assumptions about how Jupiter was formed completely, start from scratch?
DR. RICHARD YOUNG: We have to be careful. It's not true to say that most of the stuff we expected to find wasn't there. We expected to find water there; we found it. We expected to find methane there; we found it. And the significance of methane gas is that that's where the carbon is tied up with the hydrogen, so methane is the principal constituent where carbon is combined with hydrogen. We did find that. We found ammonia. We expected to find ammonia. We found hydrogen sulfide. We also expected to find that. So it's not like we didn't find things that we expected to see. They might have been in a little different abundance than we expected. This was certainly true of the helium. Apart from hydrogen, helium is the most abundant element on Jupiter. And it tells us some very important things about the way Jupiter evolved since it's been formed.
JEFFREY KAYE: Are we closer now to understanding how our own Earth formed and the solar system formed?
DR. RICHARD YOUNG: I think so. Every little piece of information we get like this is an important step forward, and the reason that we wanted to go to Jupiter is that Jupiter is the largest planet in the solar system, has over twice the amount of mass of all the other planets combined. You could fit a thousand Earths into Jupiter. In some sense, besides the Sun, Jupiter is the solar system. So if you want to understand how the solar system formed, you'd better understand Jupiter.
JEFFREY KAYE: What's next for Galileo?
DR. RICHARD YOUNG: The next for Galileo is that the Orbiter has now gone into orbit about Jupiter. It's in its first orbit, which is a very elongated orbit, and in a little while from now, I believe it's in March, they do the burn that circulizes the orbit about Jupiter, and that will begin a series of orbit each and every which there will be a post fly-by of one of the large moons of Jupiter, so we will have very close-up pictures of all the Galilean moons of Jupiter. There are four. Eo and Europa, which are the innermost two, they're the size of the Earth's Moon, Ganameta and Callisto, which are the outer two, are the size of the planet Mercury.
So in some sense, Jupiter, together with these four large Moons, forms a mini solar system. And by studying that mini solar system, you begin to get clues as to the larger solar system. And the reason that we call them Galilean satellites is they were the first Moons that were discovered by Galileo after he built his telescope.
JEFFREY KAYE: All right. Dr. Young, thank you very much.
DR. RICHARD YOUNG: It was my pleasure.
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