Greetings - Larry Lasher

>> I see the clock on the wall says 1:30 and according to our schedule it's time to start the second session. Welcome back.

This morning we had the opportunity to hear the present and former project managers describe the Pioneer mission from a spacecraft point of view. This afternoon, we want to take a look at the real purpose of a mission like this, and that is to make scientific discoveries, to advance scientific knowledge, and to rewrite textbooks for the scientific benefit of future generations.

Welcome - Wes Huntress

The theme of this afternoon's session is the science and heritage of Pioneer 10. We will hear from top scientists who worked on Pioneer about the scientific contributions made by the spacecraft and how its heritage carries on today. But first, we are honored by one of NASA's top administrators. For the past four years our next speaker has been the associate administrator for space sciences -- space science, that is at NASA headquarters. In this position--

>> ..... Silver anniversary of Pioneer 10. I already passed my silver anniversary, as you can tell. And next year I'll have a silver wedding anniversary. So I've -- there is a lot in Pioneer that I resonate with.

But today we are here to celebrate the accomplishments of this little spacecraft that could. Pioneer 10 and the sister ship, Pioneer 11, accomplished a great deal in those last 25 years.

Pioneer 10 was the first spacecraft to survive passage through the asteroid belt. It was the first to view Jupiter up close and the first manmade object to travel beyond the most distant of our planets. Now it's about 7 billion miles away, the most distant spacecraft ever. And it really is well named. It's a Pioneer. It was intended as a trail blazer. In the 1970s we wanted to go to the outer solar system. We had only been to Mars and Venus in this comfortable area of the solar system that kind of hugs the sun. But we didn't know if we could get past the barriers. The astroid belt was unknown. We didn't know how much dust was there, micrometeoroids. Could you fly a craft through that belt? We knew Jupiter's belts would be immense. We didn't know how much danger it posed to spacecraft, and Pioneer 10 was intended to find out.

It acted as a Pioneer and blazed that trail to the outer solar system. It did that well. It called back and said "you all come. It's just fine out here. You'll have to do shielding and things that kind of buffeted me around, but otherwise the door is open." In that sense, Pioneer 10 opened the door to exploring the outer solar system and beyond.

Seven billion miles; that is hard to conceive. It's more than 66 times the distance between the sun and the earth. It takes over nine hours for a slight signal to get out there, another nine for it to get back. And the radio sends only what, 8 Watts I think it is of signal all that distance. And we can hear it. For example, I have trouble seeing an 8 Watt night light across the house, much less seven billion miles.

And it's been a tribute to our deep space exploration program in this country. Pioneer 10 was a remarkable engineering and scientific achievement, and we can all be very, very proud of it. It incorporated in its time some of the newest and most advanced technologies of its day. It drew upon some of our country's best and brightest people to put it together. Our scientists around the country, the expertise of the Ames Research Center and the TRW, the prime spacecraft contractor. And so it makes sense for us to take a pause at this moment and honor Pioneer with the current Galileo mission already at Jupiter, having benefited immensely from Pioneer's exploration and soon the launch of the Cassini mission.

It outlasted its expected lifetime. I hope that is true for all of us in the room, but it certainly has done well. It opened up the door to the missions that followed. Pioneer 11, the sister ship afterwards, and because Pioneer 10 did such a great job at Jupiter we sent Pioneer 11 on to Saturn. Voyagers 1 and 2, you know. Ulysses and Galileo and soon to come will be Cassini Hoygan.

You have to remember that Pioneer 10 was the first and it remains a Pioneer today. It's searching for the point where our sun influence wanes and the effects of interstellar space takes over. It continues to go where no spacecraft has gone before. It truly is heading out of the solar system in the opposite direction than the others are going, Pioneer 11 and the two Voyager spacecraft. So it's a testament to human ingenuity and hard work, and it's a testament to human vision and hope.

It carries a message, you all know, from the people here of earth, kind of akin to a message in a bottle, and that plaque will travel with the spacecraft as long -- long after the power has run out. And it's really the symbol of a pioneering spirit that these missions represent that it's going to carry.

I hope each of you today have a chance to learn more about scientific achievements of this mission. I hope the presenters will be able to convey all the joy and excitement that comes from working on a mission like Pioneer 10.

Back in 1972, when Pioneer 10 was launched, I was really a wet nosed young scientist at JPL, and admiring the men and women who are here today and who started that mission so long ago. And I feel really truly honored to have been asked to sign this book with these ladies and gentlemen.

Back in those days, Venus and Mars were the only planets we visited, so the idea of going to the outer solar system was almost like going to the stars. It was very, very different. A whole vast difference beyond the asteroid belt, such a different part of the solar system. Giant planets, world-sized moons. It just seemed audacious and a bold thing to do. It was adventurous and exciting and very risky.

Now as we celebrate this spacecraft, we ought to take a renewed sense of excitement and adventure that is coming back now to space science and to the agency and to the planetary exploration enterprise. And so let's be as audacious and bold in the future as Pioneer 10 was in the past. It's been a glorious 25 years, and I wish you all the best for the rest of your conference.

Thank you for the opportunity to address you all.

Pioneer 10 Mission - Henry McDonald

>> Thank you very much, Wes. I take those words to heart and I'm very encouraged by them. Our next speaker was appointed director of NASA Ames' Research Center by the director a little more than a year ago. Before joining NASA, he had a career in computational sciences and engineering, most recently at Pennsylvania State University. I'd like to welcome Dr. Henry McDonald.

>> HENRY: Actually, I joined Ames Research Center exactly one year ago today, so this is my one year anniversary. And one of the first things I find out when I joined Ames, I joined Ames because I held in very high regard mainly for my own field of computational sciences, I was aware of the great work that they had done in this area. I was somewhat flabbergasted to find that part of my duties involved looking after mission control for Pioneer 10, which in my view had long left the solar system and was gone. And there it was still sending out a light Watt signal. So I was delighted at this opportunity and I was curious as to why it lasted so long. And I was told that it was just a better machine; and so I thought well, there is a catchy thing. It's a better spacecraft.

I was also curious as to why it been run out of Ames and not JPL. And I was told that in the cost proposal, Ames had been significantly cheaper. So I felt: Well, there you are; better and cheaper.

And I know that it was built and I find out today it was built in 29 months from start to completion. So I thought better, cheaper, faster. There is a catchy little phrase. I must suggest it to the administrator.

But he had already thought of that one.

One of the other very pleasant duties I had at Ames was to -- they have a retirees club there, which they call the owls. And the owls invited me over. It was a pleasant luncheon we had. One of the reasons for going over there was to specifically say thanks to these retirees for the wonderful legacy that they had left at the center, and they had left me as the director. I had a list of achievements. I had these wonderful people to look after. And it really was in very large measure the result of their prior activities and prior work. So, it was a very pleasant afternoon and I was able to express my gratitude to them.

One of the reasons why I'm delighted to be here today is that I can, in a similar manner, say thank you to all these wonderful veterans who put together Pioneer 10 for the heritage that they have left not only Ames but the scientific community. Many of the people that I regarded when I was first on the bench as heroes and legendary heroes were people associated with Pioneer 10. And it's a real privilege to be able to still look after it as it continues to send out its message to us.

Now, we will close down the Pioneer 10 mission control at the end of this month. But in the way of things, the people will transfer and they will be given a new assignment. They will be looking after a Lunar prospector. So the march goes on. But every once in awhile I have a very great suspicion that they will tune in just to hear if it's still out there and what he is saying. And I have some confidence that we have not heard the last of Pioneer 10.

So I would really like to thank the organizers for this brief period of time where I got to thank all these wonderful people for the magnificent achievement that they have and for the wonderful legacy and heritage that they have given this generation of scientists. Thank you very much.

First Mission to Opent the Door to Jupiter and Beyond - James Van Allen

>> Thank you, Hal, that was inspiring. Our next speaker is the principal investigator of the Geiger telescope on Pioneer 10. As the principal investigator on the first scheduled American satellite of the earth, Explorer 1, he discovered and characterized radiation belts of the earth, which now bear his name. His current research includes the study of the outer heliosphere. He is at the University of Iowa. I'd like you to welcome Dr. James Van Allen.

JAMES: Thank you very much. For those of you who would like to see what a Pioneer 10 really looks like, you should go to the National Aeronautics and Space Museum; look in the principal gallery there, the first one you see as you enter the main entrance to the space Museum. That is not a mock-up. That is not an artificial mock-up. That is the real thing. In fact, that was the flight spare for Pioneer 11, in case that flight had failed. It was the prime spare for both 10 and 11, and would have been actually flown if necessary. So that is a real live piece of machinery, and it's been honored for many years in the Space Museum by prominent display.

I found out that the Ames people kindly brought along -- this is a mock-up of my little instrument, the one which I've been making a living for 25 years, this little box here in the middle of the table.

My assignment this afternoon is to speak about the science rationale of this mission and the advocacy by means of which it became a reality.

I wanted to mention that Pioneer 10 and Pioneer 11 are members of what I call a third generation family of Pioneer spacecraft. And I've had a role in a good many of those, not all of them, but a good many of them. I wanted to give you a sketch of the background for the matter. First of all, there was one called Pioneers 1, 2, 3, 4 and 5. Those spanned the period before the creation of NASA, and included the early days of NASA. Two of those were sponsored by the Air Force, numbers 1 and 2. 3 and 4 were a combination of the Army ballistic missile laboratory in Huntsville and the jet propulsion laboratory at the University of Iowa. The fifth was another Air Force. All five of those were intended to go to the moon, and not one of them succeeded in doing so. But they all, each one, made a specific and in some cases important contribution to describing the structure and the extent of the radiation belts of the earth and the detail on particle composition of the magnetosphere.

I remember both 3 and 4 particularly well. 3 went out on a mission intended to hit the moon. Fell back, thereby making two cuts through the radiation belt region, which made it 200 percent successful as far as I was concerned, although it was a somewhat disappointment not to get to the moon on the part of other people. So I got two different cuts which are valuable in describing the radiation belt region and its ultimate extent.

Number 4 did a similar outgoing mission, but it did have escape velocity from the earth and went out in the general direction of the moon, but missed this. And it was so great that it was embarrassing, so that it had no resemblance to it.

So those are some of the early ones. That is what I call the first generation of Pioneers. That is from October 1958 to the first of March, 1960. You are talking about a little over two years; an intense period of early exploration.

The second generation Pioneers were those built at the Ames Research Center and for the Ames Research Center under the AARC supervision by the Space Technology Laboratories, and those were numbers 6, 7, 8 and 9. The periods which they were launched ranged from December 1965 to November 1968. Now, all of these four, 6, 7, 8 and 9, were placed in a nearly circular one astronomical radio orbits, not at the earth but in an orbit similar to the earth, roughly circular, and were intended principally for particles and fields measurements. That is measurements of the solar wind, hot gas that flows from the sun, interplanetary magnetic field and the composition of the solar wind and the intensity of cosmic rays in the vicinity of 1 AU, free from the magnetic field of the earth. And the occurrence of solar emitted energetic particles, principally protons and electrons, plus alpha particles and also heavier elements emitted by the sun from time to time in bursts coming from the solar flares.

The period of these I just mentioned was about a three-year period, '65 to '68. And an interesting note which has to do with the general reputation of the Ames Research Center for long lived spacecraft is that on the 30th -- or on the 10th of December, 1996, just a couple months ago, Ames succeeded in contacting Pioneer 6 and getting a response. It's still up there, still working, and the instruments are still on the end responding. And Pioneer 6 is 31 years old. So it is sort of the father or grandfather of Pioneer 10.

The third generation of Pioneers, built again under the supervision of the Ames Research Center, and this time with TRW, Pioneers 10 and 11, which you'll hear more about today and then 12, which I don't think has been mentioned previously today. But 12 is otherwise known as Pioneer Venus orbiter. It was launched in May 1978 and was placed in orbit about Venus. PVO, Pioneer Venus orbiter. And that continued to operate in orbit around Venus, did beautiful work for 14 years until it finally reentered the atmosphere of Venus.

I'm taking you back now to mid-1960s. This is a period in which we formulated and worked up the Pioneer missions, the new 10 and 11 missions. At that time, I'd like to recall for you the principal emphasis within NASA, like the principal space emphasis within the United States as well as in the Soviet Union and elsewhere, was on the moon as an extraterrestrial object, the principal emphasis was on the moon. The U.S., we were working up the Mercury, Gemini and Apollo missions, all intended for the man landings on the moon. That was essentially the emphasis of the agency in the early 1960s.

Now, we did have a secondary emphasis on planetary exploration, but it was a fairly low level, actually. We had a mission to Venus in Mariner 2, 1962, Mariner 4 to Mars in 1965 and the Mariner 5, second mission to Venus in 1967. I participated in all of those.

I was then a member of the space science board of the National Academy of Sciences and also of the Lunar and Planetary Missions Board, an in- house agency of NASA. And I -- and I note that we had a summer meeting. One of the first major summer studies conducted by the Space Science Board of the National Academy was held at the University of Iowa for two months in 1962, summer of 1962. And I looked through that report recently and find the lunar science received a great deal of emphasis, but there was very little coverage of planetary science or prospects of planetary exploration. And what there was had to do with Venus and Mars. And I couldn't find any significant expectation of any missions to the outer planets at that time.

Now, I was a member of both of these boards and I had a very different view of which planets were more interesting. And I made such a nuisance of myself that the chairman of both of those boards appointed me as a subcommittee chairman to develop a rationale for exploration of the outer planets: Namely, Jupiter, Saturn, Neptune, the outer planets.

These have a different character than the more familiar ones. Mars and Venus, of course like the moon, they are sort of big hunks of solid material, some atmosphere, not so much atmosphere. But they are totally different objects than the outer planets. They are principally gaseous.

Just to give you a criterion for how you tell the difference, it's done simply on the basis of density. Take the total volume of the total mass of the planet, divide by its total volume, both of these things are known from the traditional astronomical work. Take the ratio, you get a number like grams per cubic centimeter. For the terrestrial planets like the earth, you get about 5 and a half grams, more or less like a piece of rock. And the moon is somewhat less, about 3 and a half and so on. But all the terrestrial planets, which means Mercury, Venus, Mars, and the earth, have densities like 3 or 4 or 5, which indicates essentially made out of some kind of solid material or rock.

Now, the Jovian planets, which Jupiter is of course the prototypical one, has a mean density of 1.3 grams per cubic centimeter, just slightly more dense than water. And Saturn is a remarkable object and it has a density of .7. As they say, if you can find a big enough bucket, Saturn would float in it, a bucket of water. It has a density of only .7. So on those grounds they are grossly different physical objects.

Furthermore, beginning about 1957, I think, what was called nonthermal emission had been recognized from Jupiter. And in the early 1960s, that radioastronomical evidence was improved greatly, and it was then inferred gaseously that Jupiter has an enormous radiation belt consisting of electrons that emit so-called synchrotron radiation. Jupiter's magnetic field, they emit synchrotron radiation. And this distinguishes Jupiter from the terrestrial planets.

As you all know, every warm body is a radio emitter. It's hard to believe. Most of us like to think of radio transmitters as being transistors or tubes and electrons and antennas. But nature has a pattern of things. If you take a warm body that is not at actual zero, it's a radio emitter. It emits radio waves, infrared waves, and eventually like ultraviolet light. Like heating up a poker, that goes from warm to red to white. And that is a well-known thing in physics.

So, the -- even Mars, Mars is a thermal emitter. So is the moon a thermal emitter. But neither one is a nonthermal emitter. And nonthermal emission comes from plasma physical processes, electrical discharges, currents flowing in ionized gases. It's a plasma physical phenomenon in one of electrically charged particles.

So on this grounds alone we decided Jupiter was an object of great physical interest. We worked hard on developing the physical rationale for the missions, and we had the very heavy support from some of the officers of NASA. And the ones I jotted down here are ones that particularly linger in my mind as being helpful were: Don Harth, Arn Nicks. Bob -- I just saw you, Bob, out there in the hall -- Cramer, and higher levels, Homer and John were helpful in supporting our wishes on developing a mission, outer planet rationale.

So we worked up a large number of reports and recommendations having to do, putting forward our advocacy for the mission. At that time, as Dr. Huntress remarked, the outer planets were outside the pale of planning, so we ventured where no human being or spacecraft had been before to try to advocate such missions. And we segregated them according to various physical phenomena. The magnetism, we wanted to really go up there and run through it and find out what it was made of, the dynamics of Jupiter's atmosphere, which was already recognized from telescopic observation to be active.

The fact that Jupiter -- and then a large number of satellites, it could be larger by virtue of recent discoveries, there are 16 on the present count. There were known to be 8. They had a rich body of satellites. So those were the main areas of investigation.

Now, our first efforts to first -- the first fruit of our efforts really was to convince the agency that this was a worthy mission. And we had a lot of help from people I mentioned, like Bob Cramer and others, to do this. But the -- it was first approved as a new start in early 1968, and an announcement of opportunity for interested planners to propose was issued on the 10th of June 1968, with the proposals due in early December.

Now, there were 75 proposals in response to this invitation. And let me read some of the elements of that. How am I doing on time there? If you want to drop the Gavel -- I just have a couple of remarks left here. My focus is to give kind of an introduction to more specific scientific papers. Just kind of give the flavor of the subject.

And the special invitation to the scientific community, now called AO, for specific instruments and investigations, borrowed heavily from our panel reports and listed the following areas of interest. First, interplanetary magnetic fields and interplanetary particles of solar and galactic origin, out to large radial distances.

Two, articulate matter in and beyond the asteroid belt.

Three, particles and electromagnetic environment of the planet Jupiter.

Four, chemical and physical nature of the atmosphere of Jupiter and the dynamics thereof.

Fifth, thermal balance, composition, internal structure and evolutionary history of Jupiter and its satellites.

Overall objective of the missions was stated as follows "to fly through the asteroid belt and reach the environment of Jupiter."

And that was the statement which we considered a bold objective. I would say by the vice president's standards a timid one retrospectively, but that was considered a bold objective. You can see the way it was put, to pass through the asteroid belt and reach the vicinity of Jupiter.

Now, the asteroid belt was well-known in the sense that there were large numbers of cataloged asteroids, diameters of 50, 100 kilometers, and greater. It was not the problem of hitting a known asteroid, that probable was small. The issue was whether there was enough ground-up dust in the asteroid belt so it would be essentially an impenetrable hazard for spacecraft to fly through. I was a party to many of the early discussions and the general judgment about it ranged from no problem at all to impossible. Take your pick. Somewhere in the middle, which is what I think we really did. We didn't think it was trivial, but we didn't think it was impossible, either. It was unknown as to how much fine ground-up dust which would be invisible to telescopes was present in the asteroid belts, which was an milieu of pieces ground up, and it was not known what the dust hazard was.

Two of the experiments on Pioneer 10 which I don't think will be discussed today were concerned with particulate matter. And there was a beautiful machine as part of the Pioneer spacecraft, the air mattress, which is on the backside of the antenna, which was made up of a large number of pillows of sealed off gas. One of those would be triggered to the telemetry system. They had good measures on the particulate distribution in the solar system, as long as the gas in the envelopes froze out, which was well beyond Jupiter. In fact, it was just beyond Saturn.

The asteroid belt did not present a significant hazard. We knew we escaped, we got through without incident. But that is a fairly gross check. But what Kinard measured was the actual distribution of small particles. And there was no extraordinary concentration in the asteroid belt. So thanks very much.

>> Do we have some questions for Dr. James Van Allen?

>> JAMES: Yes.

>> Thank you for all the time and effort you put into this. No questions. Thank you. That was not a question.

>> It's a statement of fact, and I want to thank you very much. Excuse me. You don't get away so easily. A question.

>> I couldn't hear it very well.

>> Is there a microphone there? There is a microphone. Okay. Yes.

>> I was wondering, what is the mechanism that accelerates the electrons in the radiation belts around Jupiter to relativistic speeds? What is the mechanism? How do they get going so fast?

>> JAMES: Good question.

>> I'm glad I asked a good one, anyway.

>> JAMES: It's a good question. You can say what caused it around the earth, too. I think Jupiter is a large scale version of the earth in that respect. The radiation belts of Jupiter of course have around a thousand times the intensity of particles than the earth and also higher energy particles than the earth; so, an enormous scaled up version of the earth's situation.

But in the earth's case we have two major sources of particles in the earth's magnetosphere which the radiation belts are sort of an interior feature. First is from the cosmic ray neutron Albedo, which is a joke name for the fact that cosmic rays hit the atmosphere, make a lot of cosmic nuclear debris, among which the products of such a collision of neutrons, which of -- some of which, a small part, fly out from the atmosphere. And being neutral from the magnetic field of the earth, they are radioactive for a lifetime of about 16 minutes. So occasionally one will disintegrate on the way out. It would be an electron of energy ranging up to several MEV. But particularly it would be MEV or so. And also a proton whose energy is roughly the same as the energy of the neutron. So that is one source of particles which does not require electromagnetic acceleration.

That is probably a minor part of the answer to your question. The major part of the answer is that these particles that are trapped in the magnetosphere of the earth come mostly from outside in the form of solar wind. And they nose their way into the outer reaches of the earth's magnetic field, and then they are accelerated by fluctuating magnetic fields. You wonder why it doesn't average out to nothing, but there are trick features that on the average some lose energy and some gain energy and some lucky fellows keep gaining more and more energy and work into the deeper part of the field. So it's the acceleration of electrons. They are thought to be fluctuating electromagnetic acceleration that are most certainly the primary mechanism.

>> Thank you.

>> You will notice on the program that we do have a question and answer session from 3:55 to 4:15, so we can ask more questions.

Outer Planets and Magnetospheres - Ed Smith

The next speaker is currently the NASA project scientist for the Ulysses mission from the jet propulsion laboratory, which is going into its second orbit. And his research includes the study of magnetic fields and waves and space plasmas. I'd like you to welcome Dr. Ed Smith.

>> ED: My subject is going to be planetary magnetospheres, so I should begin by defining that for all of you. It's a region of space occupied by a planetary magnetic field. My first slide addresses the subject of planetary fields. Most of the planets have their own magnetic field, consequently most of the planets have a magnetosphere. One of the planets which we know does not have its own field is Venus. Mars we are not sure about. It has a weak field, but it might be great enough to create a magnetosphere. Hopefully that question will be answered in the next year or so. Pluto we don't know anything about. But the earth, Jupiter and other outer planets have their own fields, and they cause magnetospheres.

The fields, as many of you know, have both magnitude or strength and direction. One usually represents the magnetic field as shown here in these sort of Oval curves by so-called lines of force or field lines, a term which I'll use frequently. The tangent to the field line marked V there gives the direction of the field at each point. And the spacing between the field lines is a measure of their strength.

So if one starts near the equator of the planet, shown here, it progresses towards the pole, you'll see a convergence of field lines. The separation is smaller, which shows increasing field strength.

It's natural to ask about the origin of planetary magnetic fields. In fact, all magnetic fields originate as a result of current. In the case of the planets, the currents are located in the interior of the planet, represented by this ring marked "current." It's an oversimplified representation, just more symbolic than anything.

But it turns out that the planets which contain fluid electrically conducted cores are the source of the current which produce the magnetic fields. They are coupled to motions in the interior which are the result of heat being liberated.

One of the things that was achieved by Pioneer 10, of course, was it was the first spacecraft to pass by Jupiter. Oh, we had some indication as you heard from planetary radio emissions that it had a field, but the Pioneer 10 was the first spacecraft to actually characterize the field and measure its strength very accurately. It turned out that the magnetic field of Jupiter is far stronger than that of any of the other planets by an order of magnitude or a factor of 10. And that then for other reasons makes Jupiter really the king of the magnetospheres.

There are other important constituents, and that question of what are the other features and some of the other important constituents is addressed in the next slide. It contains the planet with the lines of force or magnetic field lines. And there are really three other items shown here. On the right-hand side are these trapped energetic particles that are known as the Van Allen radiation belts. He also mentioned by way of introduction that there are also rather intense radiowaves, which are a feature of magnetospheres including other planets. And then there is a colored Blob representing plasma.

Turn first to the trapped particles. Remember that all the particles here that we will be talking about are charged particles. There are no neutral atoms. They are all atoms from which one or more electrons have been moved to form an ion. Plus the electrons. By and large the particles, there are equal numbers of positive and negative charges, so the gases trapped in the magnetosphere are electrically neutral. The fact that they are charged means that the magnetic field exerts a force on them. That is one of the basic forces in nature.

As you see looking on the right-hand side, one of the things that the force does is it causes the particle to spiral around the field. It also has a component of motion typically parallel to the field. Referring back to the earlier slide, as the particles go from the equator to the pole, it encounters stronger fields and eventually cannot penetrate further and it turns around and travels back in the opposite direction. Those points are called mirror points. And I understand the next speaker will discuss those further. There is one in the north and one in the south. So the particles keep bouncing back and forth.

As I said, magnetospheres are generators of radiowaves and lower frequency waves, which are called plasma waves. The field lines to some extent represent an antenna as the particles and currents run along them, and then they generate intense radiation over a broad band of frequencies.

The third topic there is the plasma itself. Now, professor Van Allen mentioned that the gas, which is fully ionized, is in fact called a plasma. A plasma in the magnetospheres played an important role. The trapped radiation, although the individual particles are energetic, there are not many of them and collectively the amount of energy that they represent is a small fraction of the energy represented by the magnetic field. That's one reason why they are trapped in the way they are.

In plasma, although each of the particles have nowhere near the energy that trapped radiation has, there are many of them. In the outer field, as you go away, the strength of the field falls, the amount of energy associated with the plasma can equal the energy associated with the magnetic field. That means that those particles can exert a profound influence on what is going on inside the sphere and on such things as shape.

Pioneer 10 arrived and characterized the radiation belt. Because of the synchronotron measurements, it had consequences for subsequent missions because it was demonstrated that in fact modern solid state electronics could survive the radiation around Jupiter.

To return to the plasma, there are two effects I'd like to mention. The -- as I said, the energy of the plasma can equal or exceed the energy of the magnetic field and it can influence the rotation and motions of the magnetic field lines. The field lines in the interior planet, of course, rotate with the planet. But in the exterior regions or outer magnetospheres where the plasma can control the field, in fact the fields lines may not rotate with the planet. They may rotate faster or slower or in the opposite direction.

One of the things the plasma does also is deform the magnetic field. The next slide addresses that question. Now you don't want to think about the field lines as some kind of rigid wires. They are flexible entities and they are more like rubber bands. You'll see there are two distortions to the planetary field which you might think of near the planet as corresponding roughly to the field lines of a bar magnet.

As you see on the left-hand side, you can compress the field lines. On the right-hand side you can stretch them way out. The stretching is associated with plasmas which are trapped by the magnetic field or with them, carrying them around, and are internal plasmas. And the plasmas are such good electrical conductors, they generate current, and the current in the magnetic field then exerts force.

When the Pioneer 10 got to Jupiter, one of the things that was found was that in fact the field lines, in about the middle of the magnetosphere, stretching all the way around the planet were stretched out so much that the field lines, rather than being north/south as shown near the planet here, were essentially equatorial. That is referred to as a magnetodisk. It turns out to be a feature which is unique to that planet, Jupiter, but also because of possible astrophysical implications.

The reason for the stretching out has to do with a situation somewhat like attaching a ball to a rubber band and whirling it around. You see the rubber band will be stretched out to considerable length.

In addition to Jupiter, there are speculations that other objects have the stretched out magnetic fields because of the mass being whirled around and give things like to the magnetodisk. And one of the objects itself considered, and that is like a neutron star, there is a strong magnetic field rotates rapidly.

On the front side you'll see that some kind of external plasma setting up its current can also compress the magnetic field and push it toward the planet. That brings us to the point of what it is that is external to a planetary magnetosphere, and that is addressed in the next slide. Space is not empty but in fact has -- is filled with plasma. It's a solar plasma. It originates on the sun and is part of the Corona. It's not held back by the sun's gravitational field. That is represented here in this diagram by the orange crosses.

Now, one of the features about that is that the plasma is not simply rotating around the sun like the planets. But it's continually streaming outward in radial directions. For that reason it really represents a wind and is called the solar wind, as you see in the left-hand side of this diagram. So solar wind, it's approaching the planetary magnetic field from the left, it's a very good electrical conductor. The magnetic field keeps it from penetrating into the interior and deflects it, because it's moving around this closed volume of space, which you now see is the magnetosphere.

You'll notice that the field is compressed on the front side and stretched out in the form of a magnetic tail on the backside or downstream side or right-hand side of the diagram. There is a bounding surface called the magnetopause, which is the outer boundary of the magnetosphere. And for this type of configuration, it separates solar plasma from magnetospheric plasma.

There is another feature here which I need to comment on. You'll see this red structure, which is -- stands outside the magnetosphere. If you think about the flow of the solar wind, which has to be diverted around the obstacle represented by the magnetosphere, you can think of, for example, a river flowing past a pier. As it's diverted around the pier, a bow wave is formed, and to the first order that is what is going on here. It turns out that the solar wind is moving very, very quickly. And it moves at such high speeds that a better analogy is an airplane flying at speeds greater than the speed of sound through the earth's atmosphere. In that case, the bow waves deepens up to a shock wave, which means that the changes of the flow of the solar wind takes place abruptly in a narrow or short distance and then the solar wind is deflected around. We hear that shock wave as a sonic boom. That is what one is listening to.

When the Pioneer 10 went through the magnetosphere of Jupiter, of course it detected the bow shock and placed the magnetopause and determined the scale on which the scale exists. It's variable because of the variations of the solar wind, but it's something between 50 and 100 times the size of the planet. Far and away the largest object in the solar system.

The next slide addresses the question about the possible alternative configurations of the magnetosphere. The magnetosphere that we have just seen, the field lines on the planet originate on the planet and return to the planet. Those field lines are said to be closed. And the magnetosphere that was represented, it was said to be closed, because it prevents solar wind from entering. But the situation is more complicated, as this diagram indicates.

There is an alternative configuration called open, and it's more typical. A reason for the open magnetosphere is the fact that the solar wind is not plasma, but it contains its own magnetic field. The sun has currents, and its interior generates a field which extend up to the corona. Again, think of the analogy with the stretched rubber bands. So the magnetic field and solar wind is represented by the slanting back lines on the left and right side.

Now, whatever the orientation of the interplanetary magnetic field, there will be places on the bounding surface that magnetopause where the fields are oppositely directed, where the direction of the interplanetary field will be opposite the direction of the planetary field, shown here as closed in extending from one part of the planet to the other. That kind of configuration produces a null in the magnetic field. The strength goes to zero. Plasma with transfer from one type of field line to the other as a result. The solar wind transfer to the field line, it carries it far downstream. This is a very important process. It's called magnetic reconnection, and it leads to so-called open magnetic field lines and to an open magnetosphere.

You'll notice that the -- some of the field lines at low latitude in the magnetosphere and on the planet continue to loop around from one hemisphere to the other. But you'll see that the red lines represent these lines of force which are now open. One end is on the planet. The other end extends out into the solar wine. You'll also notice the geometry of this. The closed magnetic field lines tend to be at low latitude. And now the whole magnetosphere, the planetary one, no longer does it have a sphere shape but a shape like a doughnut surrounding the planet. The open fields tend obviously to occur at high latitudes. They are carried rapidly downstream and form a long magnetic tail. There is a boundary between the open and closed field lines which correspond approximately to the aurorae oval. It suggests and is the case that Aurora, the emission of lights in the arctic regions, is closely tied to the notion of the open magnetosphere.

I said one of the features of the open one is a long tail. When Pioneer 10 was outbound, for example, from Jupiter, it was seen that the spacecraft was actually passing through a long tail of this kind. And that showed that in fact Jupiter's magnetosphere was open and it's typically open.

There happens to be on the right-hand side you'll see another neutral point there, where the field lines again reconnect. And some of the field lines then are now connected to both hemispheres of the earth and they return inside. So you have a cutting of the field lines on the front side, reconnection on the back. So that there is no -- they feel the lines are continuously replenished and the planets don't use their magnetic field completely. So it's an ongoing dynamic system.

The final point that I would like to make has to do with again these origin of the particles, which are inside. The final slide shows a bit about some of these particles. You'd be interested to know where they originate. They can come from either inside or outside. The fact that the magnetosphere is open plays an important role here.

Look at the top side of the top of this figure. You'll notice particles that are coming in from outside. Some of them come from the sun. Basically, they are again the plasma. The solar wind plasma can access the magnetosphere through the polar cap regions because of the open field lines. Furthermore, there are outbursts of energetic particles from the sun in association with the solar flares, and those particles can come right in.

The galactic cosmic rays, which enter the solar system from outside and will be discussed later on, are able to access the magnetosphere through the open field lines. There are other sources that are interior. I mentioned here on the lower left-hand side ionospheric particles. Those particles move into the middle and outer magnetosphere.

And then on the right-hand side is another result from Pioneer 10 that was very important. Pioneer 10 discovered that the plasma inside the magnetosphere showed enhancements near some of the Galilean satellites. And it's realized those produce a lot of plasma, which contributes to the interior structure of Jupiter's magnetosphere. The moon is outside the magnetosphere and doesn't make a contribution.

The final point or two that I'd like to make is that you have a mixture of sources which are external and internal. They are accelerated by being moved around in the magnetic field. By the time the properties have been changed so dramatically as a result of the interactions that take place, it's no longer an easy matter to identify which originated outside and which were inside.

The final comment is that also some of these perturbations cause the particles to be lost. They precipitate into the atmosphere and are lost. Again, one has a system in which you must -- you have particles coming in, particles being lost and the system has to be continuously replenished. That is a lot for you. I hope you enjoyed it and learned a lot. Thank you very much.

>> Being the commissioner of food, I'd like to remind you that we have a little intermission right now. If you'd like to ask questions, all of our participants will be here to answer your questions during that period. But for right now, you can take a bit of a break and we will see you back here at 2:55. So take a little break and we will see you back here then.

BOB: I'm going to answer a few questions, at least get through a couple. One of the questions I have here says when Pioneer 10 passed by Io, was there a clue at that time that it was Volcanic? And how about Europa?

The answer is no. In retrospect we can look back at the pictures and say yes, I know what that was. At the time we just saw shadings of colors on the moons. Consequently, we didn't have a clue. So as a result, we didn't see that on the Pioneer 10 fly-bys.

Let me see here the next one. What important or special equipment did Pioneer 10 take with it? This comes from Mark at Lost Creek.

Well, I think to answer that question, you simply need to go to our web site. Take a look at the diagram which shows you the different parts of Pioneer 10, and those are explained on the two Pioneer pages, and you should be able to get the answer to that by looking at it. Basically, by important or special equipment, I assume you mean the experiments. So to be honest, I don't remember them all, either. So you'd have to go back and look at that.

What was the purpose of the postcard attached to the spacecraft? It wasn't a postcard. They referred to it as the Pioneer plaque. And if you've been listening a bit earlier, the answer to that was that it was telling people who we were, where we were, and what we were doing at the time. And, in essence, it's kind of a little ship or a little message in a bottle cast adrift with the hopes that some day somebody will find it.

How much money did it cost to fund this program in the beginning? Again, this is from Mark in Lost Creek. Well, Mark, this was a rather economical program by today's standards. I believe the spacecraft itself cost about $200 million. That wouldn't include the launch costs or operations. But for a space program, that was relatively inexpensive even by the standards back in the 1970s.

And I think that is all the questions I see right now that we will have time to answer. We will be back and get some others a little bit later on.

Questions and Answers

Dave: This is David Morrison and I am going to try to answer some of the questions that have come in on the Internet. One of the questions is: How much power do the solar panels generate? Pioneer did not depend on solar panels for power. Even at the distance of Jupiter the sun is so far away that it does not provide enough power to generate substantial amounts of electricity. So the Pioneer spacecraft, like all spacecraft going to the outer solar systems, depends on an internal nuclear thermal generator that generates its power by the conversion of heat produced in nuclear reactions. Second question was: How much did the Pioneer cost to build? In the 1970s dollars that we were spending at the time, only about $75 million to build the spacecraft. That would be something like $300 million in current dollars. When Pioneer 10 passed by Io, was there any clue at the time it was volcanic and how about Europa and its ocean? In the case of Io, we realize now that the extreme intensity of the inner radiation belts which were detected by Pioneer and which almost destroyed the electronics is due to the ejection by volcanoes on Io of ions and so in a sense, the very existence of these intense radiation belts could have given us a clue. But at that time, the idea of volcanic activity on Io was so foreign to us that no one made the connection more would you expect anyone to.

Question about Europa and its ice ocean is quite simple to answer.

There was no clue in the Pioneer data. Even the Voyager observations of Europa could at most give us a hint that its surface might be young and might consist of ice floating above an ocean. Even today, with a much better pictures from the Galileo spacecraft, we're still unsure of the answer to that question; namely, whether there might be liquid water underneath the crust of Europa.

How long will Pioneer 10 be in space?

It will be in space forever. There's nowhere else for it to go. However, we will no longer be in direct radio contact with it after this year. Because the gradually declining power available eventually will make it impossible to receive radio radiation -- radio signals from Pioneer.

How many people monitor Pioneer 10?

Much fewer than the staff of one McDonald's restaurant. Just a handful of people. It's a very lean operation and after the end of this month, even that process will be turned off as we close down the Pioneer operation center and move on to other tasks. Where was Pioneer 10 launched from? It was launched from the Kennedy Space Center at Cape Canaveral, Florida.

Is there any collaboration between the Pioneer and Voyager projects?

Yes, very much so. Pioneer was indeed a Pioneer, a Pathfinder for all the subsequent missions to the outer solar system. It demonstrated for the first time the spacecraft could safely transit the asteroid belts and it was possible to operate deep within the magnetosphere from Jupiter, without this information from Pioneer, we would not have been able to design and fly the Voyager spacecraft or Galileo spacecraft in orbit around Jupiter today. Also, the actual data acquired by Pioneer are in many ways complementary to the measurements made by Voyager many years later in the Jovian magnetosphere. We combine the data from Pioneer, from Voyager, from Ulysses and now from Galileo.

Why on did they call this probe Pioneer 10?

Well, there are two parts to that. One was why was it Pioneer and I think that was a very apt name for something that was Pioneering our capability of traveling into deep space. And it was Pioneer 10 because it was 10th in the series of Pioneer spacecraft that was launched.

Why did it say so long for Pioneer 10 to be launched into space?

Actually, it was very short. The whole time for construction of a spacecraft from initiation to launch was less than three years. Which is nearly a record for a major space probe like this.

Is there a special way in which the probe needs to get out of our atmosphere?

Yes, that's what we need rockets for. The purpose of the rocket is to lift the spacecraft beyond the atmosphere to accelerate it to very high velocities so it can escape the gravitational field of the earth and transit through the solar system out to Jupiter and beyond.

What was the educational background of the scientists that controlled Pioneer 10?

Most of them have been engineers but they're also computer specialists and, of course, the people involved in looking at the Pioneer data are in many cases, scientists, physicists, astronomers, a wide range of people involved in making a mission like this a success.