Live from the Hubble Space Telescope
UPDATE # 10
HEIDI'S RESULTS FROM JUPITER OCCULTATION
6 March 1996 - 2:37AM Hawaii
6 March 1996 - 12:40PM Hawaii
We set up on the planet anyway, and started our instrument running. It was supposed to focus on a small part of the planet where the star would be, and read out data very very fast. We were supposed to use the edge of Jupiter to guide the telescope, but because of the bad seeing, all we could see was blurry fuzziness. We took data anyway, because you have to take data. When the scheduled time of the event had passed (and we saw nothing more than blurry patches of light), we stopped the experiment and took a regular picture. We could see the star - it had popped out right on time. But because we could see the limb of Jupiter, the telescope had drifted, and we probably did not get useful data. We were all pretty depressed. But we went ahead and took all our calibration data anyway, since we may be able to salvage something when we get back to MIT and can take a closer look.
We finally shut down at 4:45 am, and then spent an hour and half taking our camera off the telescope and packing it back into the crates. Lots of sighs. We loaded up the truck and drove down the mountain, talking about how we might have done things differently, and trying to learn from this unsuccessful experience what we need to do for future events. We all went to sleep for a few hours, and now we are about to head down the mountain, to the airport, to begin the long trip back to MIT.
In astronomy, you do everything you can to prepare for your observations, but you can't do anything about the weather except hope for the best. Sometimes you win, and the mysteries of the heavens are yours to savor. Other times, the skies hold their secrets close, and all you can do is imagine what might have been.
Marc Buie February, 1996
Now that the new Pluto observations are moving along toward execution on HST, I must now turn my attention to some preparatory work. Dr. Alan Stern and I have been working on our previous pictures of Pluto. We first started to work on these images last January, January 1995, that is. That month we had time to spend on trying to understand the pictures and how to get the best information from them. Our work at that time lead us to understand that getting good maps of Pluto would not be easy. The size of Pluto makes our job very difficult. Unlike Jupiter, or even Neptune, Pluto is very small and is just barely resolved by HST. Any finite size telescope has a fundamental limit on how small an object it can make out. From the ground most modern telescope are limited at the same level by the atmosphere. In space, the resolution is completely determined by the size of the mirror in the telescope. When you work at the limit of a telescope you must understand everything about what it does in the process of focusing the light to make an image.
So, to get a map of Pluto we found that we would have to remove some blurring effects HST has on the image we see. This blurring comes from the point-spread function (PSF) and is present at some level in all optical systems, whether it's HST or your hand-held 35mm camera. When HST first launched, it's PSF was very, very bad due to a misshapen mirror. After HST was repaired, the PSF was improved but not removed. When we realized this work needed to be done we found ourselves out of time to work on this project. Alan and I both had other projects that were demanding our attentions. Alan had a rocket flight experiment to prepare and I had other ground-based observations to conduct. All of these activities distracted us until late in 1995 when we were able to return to our analyses.
All right, so what's the point here? The time-table for the Live from Hubble Space Telescope program set a very deadline for our work. After all, if we haven't figured out what is in the older data, what will we be able to do with new data? So, I've spent the better part of January and February trying to finish our analysis of the old Pluto images before we get the new data.
All of this work is leading up to a press release and a TV broadcast on our results. Thursday, March 7, Alan and I will be in Washington DC for a presentation of results which will be just one week prior to the unveiling of the new Pluto images as part of the Live From HST project. Because of the press release, I can't show you the results (yet) of our work but I can let you in on a few of the steps leading up to the release.
Our project consisted of images taken at four times such that Pluto had rotated by about 90 degrees between each time. The images clearly show regions of light and dark on the surface but need to have the effects of the PSF removed. I constructed a computer model, or description, of Pluto as it must look and then created steps in the computer that would apply all the effects caused by the PSF. From this I can then make a guess as to what Pluto looks like, blur the image, and then compare to the actual pictures. The Pluto image I want is a grid of pixels that I can relate to the brightness of it's surface. For this model I divided up the visible disk of Pluto into an 8x8 grid of pixels. Then I used my program to vary the brightness of each pixel until the collection of pixels most closely matched the image. The approach works well because we know how big Pluto is in the image. If we didn't know the size this trick wouldn't work.
Each image gives us a set of pixels that covers a part of the surface of Pluto. If we take all of these partial sets, we can add them up to get a complete map of the surface. I don't know if this sounds simple or not but to me this is pretty routine stuff. It certainly didn't sound like 2 months of work to me. But let's look at this a little closer. I was able to pretty quickly write a computer program to find the best set of pixels for each image. But, the program takes about 3-4 hours to run for each image on the fastest computer we have here at Lowell Observatory. We have 20 images in all so running all the images through the computer takes about 2 days before I get an answer. That's a pretty long time.
Have you ever written computer programs? When I was first learning to write programs, my teachers said that it was impossible to write a program that was correct on the first try. I thought at the time that this was silly. If you were really careful, certainly it must be possible to write a good program. Well, I've been doing this for nearly 20 years now and I have to say that those teachers were right. Somehow, a detail here or there will slip through and there will be something wrong with the program. Sometimes the problems are easy to spot, like all the pixels coming out completely black. Usually, the problems are very, very difficult to notice. How do know the answer is right? After all, I can't just pick up an atlas off my shelf and check to see what Pluto must look like. This is the first time this has ever been done and I have to use other means to see if the map I get out is correct. You're probably already guessing that I had a few problems along the way and you'd be right. I found a bad file name (foc410.fit instead of foc410n.fit). I found missing statements that were needed to rotate the images properly. There were others too, and each time I found a mistake that meant another 2 days before I could check the answer. Two months can go by real fast this way. In the meantime, everyone is yelling for final maps and images to get ready for this upcoming press release. At the Space Telescope Science Institute (STScI), they had to redo the press images and video animation sequences several times because of errors I found. Do I have the right answer yet? If you were asking yourself that question already, good for you. I don't know. All I can do is check answers and compare images and do my best to eliminate mistakes. I'm pretty sure I've got a pretty good map pulled out from the data but in the process there are some things that might work even better than my current computer program. Unfortunately for this press release, it will take much too long to try my new ideas so we'll just have to settle for what I've been able to do so far. Next year, maybe I'll have an even better map.
This is a pretty good indication of what it means to do original scientific research. You take an idea, some data, a bag of computer or mathematical tricks, and try to make sense of it. Along the way you learn new tricks, get new data, or get a new idea and before you know it, last year's work has been made obsolete. As you proceed, you never stop checking and re-checking your results. When you finally get the right answer you'll know because the answer is the same no matter how you get there. These new observations we'll be getting on Pluto will become useful checks of the work I've done on the data from two years ago. If nothing looks the same we'll probably have to take another hard look at Pluto to see if we can understand what we're seeing. Anytime I can get new data on Pluto, it helps me to understand Pluto a little bit better and also helps me to believe in my previous results. It also seems that for all the work, you never quite finish (at least until a spacecraft flies by Pluto and then we'll really know what it looks like). As soon as the results have been made public on March 7, I will be posting information on the maps and images we have. Stay tuned, it's only going to get more interesting from here!
PROCESSING DATA AND A CHANCE TO GO TO ARIZONATrisha Borgman
March 4, 1996
I have exciting news! I will be going on an observing run in March! The GSPC-II team (do you remember what that stands for? Guide Star Photometric Catalog II...the "phone book" of the stars) has an observing run at the Kitt Peak telescope (near Tucson, Arizona) in late March, and I will be going along! There will be two of us on the run: the chief observer and myself. I'm really excited about it!! I've never been on a run before, so this will be an amazing opportunity! I will be sure to tell you all about it!!
Last time I wrote, I talked about how I have to run the data which comes back from the telescope through many steps of data reduction in order to remove the "signature" of the telescope itself. That is all done now. But my role in preparing the data for the actual catalog isn't nearly finished! After the data has been cleaned up, I have to run it through a whole sequence of photometry reductions. Photometry is essentially measuring the amount and color of the light which comes from a star. This is what we're interested in (that's why our catalog is called the Guide Star PHOTOMETRIC Catalog).
So what do I do? Well, once again it involves many computer programs. In fact, an entire software system was developed by my boss in order to make this process run more smoothly. I am not much of a programmer myself, but I have learned how to use all of these programs. There are many steps involved, but as I said, the end result is to measure how much light is coming from the stars we're measuring, and what color the light is. The color tells us so much about how the star really works: how much energy the star generates, how old the star is, and how far away it is. All the stars we are studying are from our own Milky Way Galaxy; in fact, when you look up at the night sky, all of the stars you can see are within the Milky Way.
One of the most important steps I am responsible for is actually identifying the stars we want to catalog. The first version of the GSPC catalog was released in 1988 (I was in 8th grade then!), and I use the star charts from that version in order to identify the correct stars for the new version. This was very difficult to get used to at first. When I look at a CCD frame, I know pointed, but I still have to identify which star is which! So, I look very carefully at the star chart and compare the patterns in the chart to the patterns in my image. From there I can usually identify which star is needed. At first, I had to ask my boss for a lot of help with this part of my work--especially when there were hundreds of stars in a single image, it was so hard for my eyes to get used to locating a single star! Now that I have more experience, though, it's pretty easy--it just took time, patience, and practice!
In my biography statement, I said that I also tutor an inner-city elementary school child. I met her for the first time about a week ago--she's a 6 year-old girl named Latarsha, and we're having a lot of fun together. It's an amazing challenge to try to teach someone how to read, or how to understand addition. I see her twice a week, on Mondays and Wednesdays, for about 2 hours each time. It's a great study break, and I really enjoy doing something to help people.
Look at the time!! Well, it's time for me to meet Latarsha! Have a great week, everybody!!
Howard H. Lanning
February 26, 1996
Mondays start off like just about any other day, but often times more chaotic than most, and today is a classic example. I arrived this morning to the usual 60+ email messages including various reports, notices, and problems. It often takes the entire day just to get through the messages because of the diversions and problems one has to deal with from the start. And right off the bat today is email from a PI who has identified a problem with his proposal and needs some help. The first step is to forward the mail to the appropriate individual within the Institute to try and resolve the issue. While waiting for a response, I sketch out a short list of the items that must be done today. While doing so, a call comes in requesting me to attend a meeting tomorrow for a discussion on software related issues to consider for long term improvements, mainly with an effort to provide more input from the scientific side of the fence. Ok, will do. That's two meetings tomorrow already on the schedule.
I continue working my way through the email and come across another proposal problem. This case is a possible duplication of science being done by two different astronomers. Such is not unprecedented since this type of check can't accurately be done until all proposals are received for a given cycle, and as the programs are being worked by the Program Coordinators (PC), or changes occur to certain programs, these things keep popping up. I do some double checking with the target list and formatted list of the affected proposals, then respond to the email providing my comments. Often, in the case of true duplications, we must recommend data to be obtained by one of the scientists be embargoed, i.e. not be allowed to release for publication, until the other executes and is no longer proprietary. This means some science can be on hold for up to a year. Well, that's chewed up a good part of the morning and I still haven't made it all the way through the mail and reports.
Just after finishing the investigation and sending out my comments, I get another call from one of the Instrument Scientists (IS). Turns out we have another proposal which needs to have a more accurate centering sequence put in to prevent the program from failing. After discussing the situation at length with the IS, and getting all my notes together, I talk to the PC, informing her what we need to do. I then call the astronomer who is 2 time zones away to discuss the details and suggest he send in a statement of the problem and scientific justification which I'll append to my summary of the change to be requested. Basically, the centering maneuver will take so much time, that we must ask for an additional orbit to assure success and prevent taking time away from the science exposures. Once the astronomer sends in the memo, I can put everything together and send it out to the rest of the committee which will vote on the change request and then send a recommendation to the Directors Office for consideration.
Well, now I've got 15 minutes to complete my monthly research status report. Done. Now on to reviewing submitted Cycle 6 proposals. I have a stack of Phase II drafts of proposals to review which had been placed on the chair by a PC. These are the detailed submissions including the targets, and all activities including acquisitions, peakups, exposures, calibrations, etc. that the astronomer wants to do. It is the CSs task to verify that the current format of the proposal is acceptable with respect to the science to be obtained, i.e. will the astronomer get what he/she wants, and is the proposal structured to provide an efficient use of the spacecraft? I manage to get through four proposals, talking to the PC on one them, before finally getting to take a short break for a bit to eat. I usually end up eating at my desk through my lunch hour because there's so much to do. But while taking a stroll down the hallway to pick up my mail, I get cornered an asked to attend yet another meeting tomorrow. That's three! Back to the office to put it on my calendar and to send a notice of approval to my PC about the proposals I just finished reviewing.
To get documentation for the latest meeting, the head of the committee indicates I need additional system configuration privileges set up. So email is sent to the system managers. There always seems to be some little thing that hasn't been setup, or is a new feature I need. So, just as with proposal problems, these things pop up from time to time.
Next, I need to determine the status of the GHRS Calibration Plan in order to provide a report to the Data Quality Committee later this week. Off to an impromptu meeting with the calibration Instrument Scientist. From there, I take a short diversion to discuss some Data Quality issues with one of our Data Analysts, since we're trying to put together more details for procedures and products to be delivered to the astronomers.
Upon returning to my office and jotting down my notes, more email to read. It never stops. All day long we get mail coming in. The latest is the change request from the astronomer I talked to earlier in the day. I put together the summary and all details and send it out to the committee for review. It's now 5:30, but I still have 3 more hours to go. Twice a week, while my wife is in class at Johns Hopkins University, I was late putting in about 10-11 hours. I begin the review of the remaining two proposals left by my PC, and a quick review of the material to be discussed at two of our meetings tomorrow. Even though it is late, another Institute Scientist comes in around 7pm to ask questions about another instrument. This time I can't help, but often, I can. Since I used to work in the Planning and Scheduling System as the Lead Operations Astronomer for Proposal Preparation, I had to know something about all the instruments being used. It's training and expertise that often comes in handy.
Around 8:30 I finally finish for the day, and believe it or not, I actually have completed most of the items on the short list of things to do despite all the diversions throughout the day. A rare treat. Still got a couple that won't get done for another two or three days because of the meetings tomorrow, but then, I'll just put them on the next short list for another day.
NASA PRESS RELEASE: 96-43
March 7, 1996
Hubble's snapshots of nearly the entire surface of Pluto, taken as the planet rotated through a 6.4-day period, show that Pluto is a complex object, with more large-scale contrast than any planet, except Earth.
The images also reveal almost a dozen distinctive albedo features, or provinces, none of which have ever been seen before. They include a "ragged" northern polar cap bisected by a dark strip, a bright spot seen rotating with the planet, a cluster of dark spots, and a bright linear marking that is intriguing the scientific team analyzing the images. The images confirm the presence of icy-bright polar cap features, which had been inferred from indirect evidence for surface markings in the 1980s.
This historic new look at Pluto helps pave the way for a proposed Pluto flyby mission early in the next century. Pluto is the only solar system planet not yet visited by a spacecraft.
"Hubble is providing the first, tantalizing glimpse of what Pluto will be like when we get there," said Dr. Alan Stern of Southwest Research Institute's Boulder, CO, research office. Stern led the team who used Hubble to obtain the most detailed view yet of Pluto. The Pluto imaging team also includes Dr. Marc Buie of Lowell Observatory, Flagstaff, AZ, and Dr. Laurence Trafton of the University of Texas, Austin. This team of planetary scientists used the Faint Object Camera aboard the Hubble to obtain over a dozen high-quality visible and ultraviolet images of Pluto in mid-1994. These images have now been carefully reduced and analyzed.
"These results and the maps we constructed from them are much better than I ever hoped for," said Buie. "It's fantastic. Hubble has brought Pluto from a fuzzy, distant dot of light, to a world which we can begin to map, and watch for surface changes. Hubble's view of the tiny, distant Pluto is reminiscent of looking at Mars through a small telescope," said Stern.
Some of the sharp variations across Pluto's surface detected in the Hubble images may potentially be caused by such topographic features as basins, and fresh impact craters (as found on Earth's Moon). However, most of the surface features unveiled by Hubble are likely produced by the complex distribution of frosts that migrate across Pluto's surface with its orbital and seasonal cycles. Pluto is so far from the Sun that even nitrogen, carbon monoxide, and methane gases partially freeze onto its surface during the long period (about 100 years) when it is farthest from the Sun.
The Hubble images reveal much more surface variety on Pluto than on other icy objects in the outer solar system, including Pluto's often-cited twin, Neptune's large moon Triton. According to Trafton, "The HST images are confirming Pluto's individuality. It isn't a twin of Triton after all."
During the short, warm season around Pluto's closest approach to the Sun, these ices sublimate (go directly back to a gas), thickening Pluto's atmosphere. "The light areas are as bright as fresh Colorado snow, and the darker areas are more reminiscent of the brightness of a dirty snow," said Stern. The darkest regions likely result from hydrocarbon "residues" Pluto's complex chemical melange of surface ices.
Pluto is two-thirds the size of Earth's Moon, and 1,200 times farther away. Pluto's apparent size in the sky is so small (0.1 arcseconds, which equals 1/36,000th of a degree), that 18,000 Plutos would need to be lined up to match the diameter of the full Moon. This puts Pluto's surface below the resolution limit of the largest ground-based telescopes; as a result it has been impossible to directly see any significant detail on Pluto before these Hubble observations.
Viewing such a remote and small body has been so difficult that Pluto's moon Charon wasn't detected until 1978, despite the fact that Pluto itself was discovered by Clyde Tombaugh in 1930.
Shortly after its launch in 1990, the Hubble Space Telescope first peered at Pluto and clearly distinguished the planet and its satellite (which is only 1/3000-th of a degree away) as two separate objects. However, a detailed look at Pluto's surface had to wait until Hubble's optics were improved during the 1993 servicing mission.
The Advanced Camera, planned to be installed on Hubble in 1999, will yield slightly better images of Pluto. This will be the best view of the distant planet until space probes eventually make the long trek across the solar system.