Jupiter

by Prof. Reta Beebe

What I would like most to know is, what are the processes that make the winds blow on Jupiter. The winds are much, much stronger (than on Earth: ed), and I can rationalize the fact that, well, yes, because it's such a dense bank of clouds and there's really no solid surface, there's no friction that there is on Earth to destroy the winds. But when I look at the wind pattern, from the equator up through seven degrees north latitude, twenty degrees... I find jets, and the wind increases surprisingly rapidly, and then drops off surprisingly rapidly. I don't understand the processes that create such narrow jets. We have jet streams in the earth but they are quite broad, but here (on Jupiter: ed) the better the spatial resolution I get on my images, the narrower my wind jets are, and I do not understand that process, and I would really like to know.

(In addition to more general interest in Jupiter, Prof. Beebe -- as a member of NASA's Galileo team -- thinks the PASSPORT TO KNOWLEDGE Hubble observations could make a great contribution toward understanding the precise place where the Galileo atmospheric probe will plunge into the giant planet's dense, roiling clouds: ed)

We have the Galileo Probe going in on December 7th. and we know the latitude and longitude relative to the core of the planet, but the winds are blowing across that from West to East in such a way that they are carrying the clouds around the planet, and the clouds will be shifting eastward 7 and half degrees a day, so that the nature of the cloud area that the probe is going to go through is a big question. We (already: ed) have HST observations in October and scheduled for February, and we will assume the winds do not speed up or slow down, and we will interpolate and say that is the cloud it went in, but if we had even just one orbit in March to compare with the February and October, it would help to substantiate the fact that that assumption was true.

...And then the students that were collaborating here could also access these images and that would allow them to see what was happening... they would be able to access the Web pages that have been assembled at (NASA) Ames Research Center, about the analysis of the probe. Because by the time the students get their observations in March, the people at Ames will be reducing the probe data. So there is a lot of interaction there. And this would be a valid interaction because it would further substantiate the condition... how rapidly it was changing.

Why are the observations important?

The thing I find most fascinating is that the more I learn about this planet the more it's like the earth, and it seems so much unlike the earth. Here's a planet (where) two thirds as much energy is coming from below the clouds as is coming in from the sun so that this atmosphere is being heated from above and below. In the case of the earth's atmosphere, the sunlight -- a lot of it does come through and hit the surface and so it is bottom-heated. So the processes that go on are much more similar than you might think. The other thing that I have found, as I have worked on Jupiter, is that although I can't see what's happening down below it obviously strongly influences how the winds blow, how these large storms are maintained, and that sort of thing.

And when we attempt to study the earth's atmosphere we have the same thing with the oceans. Recently we have become aware of El Nino, major upwellings, and how it totally modifies the climate of the earth, so the more the learn about these two (planets) the more they become similar rather than dissimilar...

What made me want to become an astronomer anyway?

I grew up in the hills of Colorado. My father was a farmer/rancher... I did not realize that my father was also a naturalist, who'd done a lot of study on his own, because he'd never even gone to high school. So I just assumed that almost everybody in the whole world knew everything that my father did. I learned to pick out the constellations. I spent my childhood trying to say "money" three times before a falling star disappeared, because I would get rich. So that I had a very rich natural environment, animals all around me the whole time, we lived on a ranch. My mother was a teacher and very interested in education, history, that sort of thing, so... she did not answer our questions, she sent us to a book. So it became logical to use a book.

My brothers were all very much younger than I, so I was pretty much free to be what was frequently called the "wild woman". My father used to claim that he had to get the horseshoe rasp out to get my feet in shape to send me to school in the Fall, because we really did run wild, wonderfully wild, in the summertime. And I just simply learned to enjoy the out-of-doors.

When I started teaching, part of the motivation for starting teaching was that I had the summers off to do the kinds of things that I wanted to do. I was teaching in Colorado, where I grew up, and we ranged through the state, you know, on projects for the geology that we would be teaching in junior high. And the space program was developing, and I decided I was not smart enough to continue teaching in junior high, so I went back to get some more training, and had so much fun, I just stayed.

How can the Hubble Space Telescope make unique observations of these planets, and how many orbits will it take?

There are basically two kinds of planets in the solar system. There are the earth-like planets and the large gas planets, and I consider Jupiter to be the most accessible of those large gas planets. As you go farther and farther into the solar system, the outer region of these planets get colder and colder, and you have to stare deeper and deeper through hazes to see the cloud structure. In Jupiter's atmosphere you can see the active motions of the clouds which are marking what the atmosphere is doing, so that the ammonia ice in Jupiter's atmosphere acts like a marker, as does the water ice in Earth's atmosphere.

When you are observing with Hubble, it's a black and white camera, there's no color detected by the camera itself. This camera is capable of seeing light much farther in the UV (ultra-violet segment of the electromagnetic spectrum: ed.) than we are used to thinking about, and farther into the infrared that the human eye can see. In front of the camera there is a filter wheel device. You can select the filter you place in front of the camera. That determines the color of light that is coming through to your camera. In one orbit of the spacecraft, since Jupiter is such a bright object, we can get about ten images. So that you can select a series of colors. You could look in the UV, the near UV, blue , green, red, and use your blue, green and red to make your color image... Then you can move on out to the near-infrared where methane gas absorbs very strongly in some colors, and there are a pair of filters aboard Hubble that allow you to take one image where the methane gas is absorbing so strongly that the photons of light that go in have little chance of coming back, so anything that appears bright in that image are high clouds, or hazes, that reflect the light before it goes down and is absorbed by the methane. The other filter is so designed that it only allows a band of light to pass in a region that methane gas does not absorb, so the light goes down and reflects off of the ammonia cloud deck. And when you compare those two you have a very good measure of which clouds are high and which clouds are lower in the atmosphere... (the) vertical structure, which you can then compare to what you see in the earth's atmosphere.

...It's quite possible that we could schedule the observation so that we could have (Jupiter's colorful volcanic moon: ed.) Io crossing in front of Jupiter, and then we would observe it (Io) in a series of colors. Now Io is so bright itself that -- it reflects so much of the sunlight -- that if we were attempting to take a methane picture of Jupiter, Io would be over-exposed, it would be just a white blotch. But it does not damage the cameras, so this would not be a major problem.

But, one of the most interesting things is (that) if we knew more about what makes the winds blow on Jupiter, and the general circulation and heat balance of that atmosphere, then that would help us understand Saturn. Then we have the Cassini (spacecraft) mission -- a large flagship spacecraft, probably the last we will ever have of those, being developed for a launch and arrival just after the turn of the century. It will go into orbit around Saturn, take quite a few observations of Saturn, drop a lander into Titan -- it's carrying a radar mapper to map the surface of Titan -- so that this kind of study we are doing now, in conjunction with the limited information we can get from Galileo, can be the basis for a even better understanding of the twin sister of Jupiter.

Students that are in high school and early college now will join the Cassini team as time goes on -- these projects take so long that people that do the major part of data reduction were in elementary school when we started them!

What's the best, and the worst, thing about working with the Hubble Space Telescope?

The best thing about working with the Hubble Space Telescope is that I don't have to deal with earth's atmosphere. When you are using a ground-based telescope, you have the probability of storms coming across... but that's not the worst part. The worst part is that the atmosphere jiggles in front of your view. And it does not matter how short you make the exposure, or how hard you try, there's a fundamental limit of what you can reach. HST orbits the earth above the atmosphere, so not only do I get rid of that jiggling, the spatial resolution that I get on my images depends on the camera itself and it's always the same. I can observe in the ultraviolet, and that light won't even get through Earth's atmosphere, and I can observe in the infrared much more efficiently than I can from the earth. If I get the data, it (all) matches ...in a very systematic way.

The biggest problem with using the HST is that it's in low earth orbit. This is nice, because with the Shuttle as our only repair mission (vehicle: ed.), you have to be able to access it, and it has to be in a low orbit to do this. But this then requires that it orbit the Earth every hour and a half, and I have only about 45 minutes during that period when I can observe Jupiter. So every hour and a half I get (only) about 50% of the time observing the planet. In order to lock on with such a rapidly-moving telescope, the details of observing are horrendous. These things have to be scheduled far in advance, and the net result is that to make this an efficient operation you have to formulate your whole observing program, and it has to be stacked carefully in queue.

Why is the Internet a unique tool to connect students to real science and real scientists?

I think the Internet is a fantastic device. Not only do I get communications regularly from people who just have fundamental questions that they ask, but I also get communications that are almost impossible any other way. I can talk to a planetary astronomer in Alma Ata (sic), over by the Tibetan border, 2 to 3 times a day on the Internet, and if I were to attempt to send him anything in any other form it takes months for him to get it. So that not only would the Internet provide a way for students to talk to working scientists in this country, it gives them access to the world.

I have been working with students most of my life. I taught in Junior High before I went to graduate school. But I have actually been teaching for thirty five years. At New Mexico State University, professors are teachers first and researchers second. We have large educational outreach programs locally. I worked on the Voyager project, I had a considerable amount of outreach in that. Recently New Mexico State University was selected to become the atmosphere node of the NASA planetary data system. So that we are basically working on archiving and documenting and preparing data for general use of the whole scientific community. So we are in a position of being a very effective source of information for students who are working on this.