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OFJ97 Field Journal from Glenn Orton - 2/21/97

So much has happened since the last time I logged an entry into the Online From Jupiter journal almost a year ago!

Some things have gone according to plan for Galileo, and other things are working very differently.

My basic plan has always been to make a comparison between the Galileo Probe and the orbiter's observations of the Probe descent region in the atmosphere. But, there *were* no Galileo orbiter observations when the Probe was going in, as a result of Project conservatism with a faulty tape recorder on the spacecraft. We had to work only with Jupiter images taken by ground-based telescopes, like the NASA Infrared Telescope Facility in Hawaii and other places. All this was kept in my last journal entries, and out of this work - a collaboration between people working at many different observatories - came a publication in the widely-read and fairly prestigious scientific journal Science.

Not only that, but our last infrared picture of Jupiter (showing its cloud- top heat emission) was used as the cover for the issue (May 10, 1996) that described all the initial scientific results from the Galileo Probe.

The observations kept on coming and coming, at least once a month, and my flying time kept climbing and climbing in order to go out to the NASA Infrared Telscope Facility (IRTF), at the summit of Mauna Kea on the "Big Island" of Hawaii. That's good if you want all the frequent flyer miles, but bad if you have a family and want a life! In fact, when all the excitement happens at JPL during each orbit encounter period, I'm off at a distant observatory catching glimpses of the real planet (the spacecraft is much too small to see out there, but - I might imagine where it is when I see the planet).

*The first orbit encounter: Ganymede-1

For the first orbit encounter in late June, we were at the NASA Infrared Telscope Facility (IRTF) and managed to have rather nice weather, with snow flurries clearing up in time for our observations of Jupiter (yes, snow in Hawaii; it is nearly 14,000 feet above sea level, and the oxygen pressure is just a little over 60% of what it is at sea level).

Not all was well with the spacecraft's instruments. One of the cameras (the Photopolarimeter-Radiometer (PPR) instrument) was to take extremely precise measurements of light reflected back from Jupiter, as well as measure its temperature. In order to do this, the PPR has to use several different filters, which are mounted on a wheel. That wheel had gotten completely stuck, meaning that PPR couldn't make those measurements.

This was fairly devastating news. We had wanted to make lots of measurements of temperature to see what powered the winds. Temperature differences between different locations can do this, just like the temperature difference between, say, the equator and the polar regions here on earth do. We also wanted to see how the cloud-tracked winds corresponded with these predictions. This would allow us to see what other sorts of forces were acting on the wind and cloud fields.

There was a brief break for a family vacation in Paris while I gave a talk about Comet Shoemaker-Levy/9 (which crashed into Jupiter). This ended up being a very mixed vacation, with Linda getting sick with a terrific cold and staying in bed for the first week, and my mother and kids starting out each day fresh, but getting tired and grouchy each day and complaining that things weren't like they were at home at all. The kids were happy to return to their beloved summer camp back home.

And then, my life as I knew it completely changed for many months...

The trouble with clouds - on Jupiter or anywhere else - is that, while we'd picked the types of features (such as "white ovals") we wanted to examine many months ago, sometimes those particular types of clouds just wouldn't be there when we got there. They could easily change shape, form in different places, or just VANISH without warning! It was clear that our IRTF observations were going to be absolutely necessary to ensure that the spacecraft was going to be pointed at the features we wanted on the next several orbits. I discovered that, lacking anyone else doing this work, it was going to be pretty much up to me to judge when in each orbit we were going to be looking at the planet and which location we were going to be looking at to get the atmospheric features we'd planned on for the last two years. I was going to be doing a great deal of work in the months to come.

*Ganymede-2 and the rush to publication for G1 results:

We went through the G2 orbit without the Photopolarimeter Radiometer (PPR) turned on. This was the Project being cautious: they wanted to make sure that the instrument's attempts to move its stuck filter wheel would not do itself further harm or harm other instruments (see my Ganymede-1 journal for details on what happened). There was not enough time to transmit to the spacecraft revised instructions telling the PPR to not move the filter wheel. The only solution was to turn PPR off. This meant, importantly, that there was no information on temperatures in the atmosphere when other instruments were taking atmospheric data except what we obtained from infrared telescopes here on Earth.

The thermal imaging data from Hawaii's Infrared Telescope Facility (IRTF for short) during the G2 encounter were breathtaking. In some cases, they were as good as some of the distant Galileo NIMS (near-infrared camera/spectrometer) "global" observations of the planet! We also got to use the University of Hawaii 88-inch telescope. Jupiter was "up" in the sky for only part of the night, so we used the rest of it for Saturn, Neptune, Uranus and Mars, as well!

Almost all of the PPR data (taken before its filter wheel got stuck) were from long wavelengths which were sensitive to the radiometric heat output from Jupiter and its satellites. We were preparing for a nice, leisurely time of writing up our results. Then the project scientist, Torrence Johnson, announced the deadline for the initial articles on what we had learned from the G1 orbit data would be due the next week. This meant we had all of 10 days to have numbers and come to great conclusions from them.

That wasn't enough time. What we submitted for publication suffered from the pains of being brand new data which we didn't wholly understand. Also, the PPR was essentially a single-element detector (for comparison, the CCD in a camcorder can be 1000 elements wide and 1000 elements long), and there are perils when making images or maps from data taken by a single-element detector scanning across the planet. The reviews of the article were critical of the fact that this was painfully evident, and one suggested that we not publish what we had: our article was rejected. This hurt. Something similar had happened to our article on the Venus atmosphere and the PPR became the only remote sensing instrument without a publication in the issue of Science where all the other instruments that took data at Venus were represented.

We started looking at the data again. I began to work on ways to invert the data numerically to determine the temperature at different atmospheric levels, rather than just report what the temperature seemed to be from the thermal radiation we detected. Then, I got a call yet another call from Science - could we please submit a new article by the next day? I asked if I could please have at least the weekend, and I spent all of Friday, Saturday and Sunday working without sleep. It was awful! But the article ended up being fine. Our data showed, for example, that the inner dark part of the Great Red Spot (our primary target on the first orbit enounter) was quite cold and probably represented gas moving upward rapidly.

Galileo wasn't the only science news of the day. While we were examining a planet in our own solar system, other scientists were continuing the search for planets outside our own solar system. At a meeting, I heard about evidence for at least 10 solar systems around normal stars...that REALLY was news to me!

The last thing to happen during the G2 orbit was getting to use the 10-meter Keck telescope--the largest "optical" telescope in the world. The thing that controls how small the features are that we can see for very long wavelengths is diffraction - that is, the light waves passing and hitting both sides of the primary reflecting mirror. The bigger then mirror, the smaller the size of things you can resolve. The Keck is a VERY impresive telescope, but our half night there was a miserable failure, with nothing going right. We later applied for more observing time but were turned down; the lion's share of Keck time given to NASA is for searches for extrasolar planets, so we thought of our getting any Keck time as fortuitous at best.



 

 
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