by Mike Brown
Wide areas of the sky! This was just what I needed! The study of the Kuiper belt, still in its youth, was hampered by the fact that astronomers had been searching for objects in the Kuiper belt with digital cameras that covered only small areas of the sky at once. They were successfully finding objects, but the objects were all small and faint. Imagine being interested in exploring the inhabitants of the ocean but all you have is a small handheld net. If you dip your net in the sea many times, you will certainly find a vast collection of microbes and krill, but you will never know that there are dolphins and sharks and even the occasional whale. In contrast, the photographic plates from the 48-inch Schmidt were not nearly as sensitive as the digital cameras that other astronomers had used—the net was so large that the krill and the microbes would fall right through—but we had a net big enough that we could cover the whole ocean. The big fish would have nowhere to hide.
I thought about the biggest fish.
I had already been thinking by this time that Pluto might not be a solitary planet out there in the Kuiper belt; there might be others still to be found. And using the Schmidt was clearly the way to find them. There was a major problem, though. The last time I had touched real film was when I was in third grade and my father and I had built a little darkroom and developed our pictures from the pinhole cameras we made. There was no way I could carry off this project. I gingerly inquired as to what Jean was doing next fall, when the telescope was to be idle. She didn’t know. She and her coworker would presumably be assigned other tasks around the observatory during that nonworking season. And what if someone else was interested in using the telescope? I asked. Her face lit up as she quickly exclaimed, “I’m sure everyone would be thrilled—we would love to have new projects on the telescope.”
Then she asked: “Do you think we might find a planet?”
• • •
And so I came to be looking for planets. A year later I got to know Jean and her coworker Kevin Rykoski extremely well, as every night, except for bright time, when my nemesis interfered, I called in to talk about what section of the sky to photograph that night. Every night, in all possible permutations, we discussed the position and phase of the moon, the possibility of clouds or fog, and the success or failure of the pictures from the night before. Everywhere I went I carried my hardbound notebook containing maps and calendars and records of everything that we had done to date. Every night, no matter what time zone I was in or continent I was on, I called in to the 48-inch Schmidt precisely thirty minutes before the sun set (the time of which was recorded for every night in my black notebook). I remember making the call from a pay phone on a busy evening street in Berkeley, early in the morning from a hotel in northern Italy, well past dark from my mother’s house in Alabama, but most of all from that little cabin in the woods.
I had meticulously worked out the procedure. Every month we would cover fifteen separate fields, or an area that covered a little over 1 percent of the full sky. While that doesn’t sound like much, in just a single month we were going to have covered more sky than all other astronomers searching for Kuiper belt objects had covered in the preceding five years. On a typical night, we would try to cover three or four fields. To do so, Kevin or Jean would walk from the dimly lit control room crammed with computer equipment and go up a winding set of stairs to the floor of the telescope dome. Once inside, all of the lights would be put out as they would unpack one of the photographic plates from where it had been stored in a light-tight box. From my pinhole camera days I remembered that film was developed in red light, which doesn’t affect it. But these photographic plates were designed to be especially sensitive to red light, as objects in the Kuiper belt tend to be on the red side. All of the work on the plates, then, had to be done with no lights whatsoever. When the plate was unpacked, it would be walked to the telescope and inserted into the base. Only then was the shutter of the telescope opened and the light from the sky allowed to beam onto the plate. Thirty minutes later, someone would again walk to the top of the stairs in the dark, take the plate out of its holder, and then walk to the other side of the dark dome floor and place the plate into a miniature manual elevator and drop it down to the other person who was waiting in the darkroom below. The person on the dome floor would get a new plate and begin looking at a new patch of sky, while the person in the darkroom washed the plate in a succession of developer and fixer fluids until, about the time that the plate was finished, a new plate would appear in the miniature elevator. In the morning, before going to sleep, Jean and Kevin would look at the crop of pictures from the night. Some would be smeared or have defective photographic emulsion and have to be rejected, but the good ones got labeled, put into the cabinet, and filed on my list. The next night we would review what had happened the night before, discuss the weather forecast, curse the encroaching moon, and start over again.
I found this exhausting, and I was the only one of the three of us actually sleeping at night.
The goal was to get three good images of each of the fifteen fields during the course of the month. Ideally they would be taken three nights in a row. My job was to examine each of the images and, as astronomers had been doing for two hundred years, look for the things that move.
Kevin and Jean must have been happy that the moon existed, since bright time was the only time that they got a few days off. But I was no fan of the moon. I became increasingly agitated as the month progressed from gray to dark to gray again and finally the bright approached. Invariably as the month was coming to an end we would be behind schedule owing to problems with the weather or problems with the photographic plates. I would count ahead the number of nights left before bright time commenced and almost always find that everything had to go perfectly or we would lose one of our fields. And every lost field meant that any planets out there in the sky suddenly had a huge place to hide. Our net would have holes. Near the end of the month, Jean and Kevin would invariably work overtime. I could do nothing except sit in Pasadena, stare at the moon, and fret.
Somehow, we managed. In two years of surveying the sky with the 48-inch Schmidt Telescope, we actually managed to get every image of every field we wanted except for one. We mostly beat the moon. Final score: 48-inch Schmidt, 239 fields; moon, only one field. Those 239 fields we had covered were only about 15 percent of the whole sky, but it was, we thought at the time, the right 15 percent. The moon and planets are all strewn across the sky in a giant ring encircling the sun, and we had looked at that ring—as well as a good bit above and below—for a period of about four months, or one-third of the whole ring. So while we had looked at a relatively small fraction of the sky, it was much of the interesting sky, and it was enormous compared to what had been previously examined. We hadn’t taken our net through the entire ocean, but thought we knew one of the whales’ major swimming grounds, and we had trawled it all.
Looking at vastly more sky than anyone else had ever looked at for large objects out in the Kuiper belt was so immensely exciting that I could hardly contain myself. I knew that there would be big discoveries, and having new pictures come in night after night after night with only a break for the full moon kept everything at a constant peak. I talked to my friends about new planets. I thought about names for new planets. I gave lectures about the possibility of new planets. I did everything I could, except find new planets.
Of course, I did more than talk on the phone and make sure that the pictures got taken. After each set of pictures was exposed, the photographic plates would be put into large wooden crates and shipped from the mountaintop down to my office in Pasadena, where my work would begin. I needed to turn those crates full of plates into discoveries of planets.
Seventy years earlier, Clyde Tombaugh found Pluto by doing almost exactly the same thing that I was currently doing, except that he did all of the work himself. He would stay up all night exposing the photographic plates to the sky, and then in the daytime he would look for things that moved. To look, he would take a pair of p
hotographic plates that showed the same region of the sky and then load them into a specially constructed apparatus the size of a large suitcase, called a “blink comparator.” Inside the blink comparator, a light would shine through one of the plates and project an image toward the top, as if the photographic plate were a giant slide. On the outside, Tombaugh could look into the comparator with an eyepiece and have one of the slides projected into his view. The special part, though, was a little mirror inside that could quickly flip back and forth so that Tombaugh could look at one of the photographic plates and then the other in as quick a succession as he wished. All of the stars in the sky, all of the galaxies, all of the nebulae, would appear the same on each of the two plates, but anything that moved or changed or suddenly appeared would jump out as the two photographs were blinked.
Palomar Observatory had had a similar apparatus to Tombaugh’s in its early years, but it had been disassembled a couple of decades earlier. But even if such a thing did still exist, it would have done me no good. Because the telescope that I was using was so much more powerful than the one Tombaugh had used to find Pluto, each of my images showed one hundred times more stars, and thus would have taken one hundred times longer to have gone over by eye. Early on in the project, I calculated that to look at every star on every photographic plate by eye would have taken me forty straight years of staring into the blink comparator and slowly watching pictures of the sky go by.
Not wanting to wait forty years, and it being 1998 instead of 1930, I put the computers to work instead. First, we needed to scan the photographic plates to get them into digital form, and then the computer could do the rest. The scanning was quickly done on a big machine that already existed. Getting the computer to do the rest, though, took longer. There is no software package that looks for planets. I would have to write it myself. Though I knew nothing about emulsion and developer and fixer, this I could do. This I was good at. I had been writing little computer programs to analyze and predict and follow the stars and moons and planets in the night sky since high school. This would be the first program that actually mattered.
I spent most of that year slouched in front of a computer screen in my office, testing, scowling, starting over, typing furiously, and pondering. For someone looking for planets, I spent an awful lot of my time looking at computer code and numeric outputs instead. My nights were spent not outside staring at the sky but inside staring at numbers and computer programs and doing every test conceivable. I needed to make sure the software wasn’t going to make any mistakes. I wanted to make sure that I didn’t do anything stupid that made me miss planets that were right in front of me.
I made the computer begin by looking at a triplet of scanned photographic plates. It examined each of the little blips of light on each of the three images taken over the three nights. All of the stars in the sky, all of the galaxies, all of the nebulae, had the same coordinates on each of the three photographic plates, so the computer quickly identified them as not moving and tossed them aside. Sometimes, though, something appeared at a spot in one image where the other two images showed only blank sky. The computer took note. It could be many things. Sometimes stars in the sky get brighter and suddenly show up where they weren’t seen before. Sometimes satellites in orbit around the earth give a sudden glint that looks like a star. Sometimes dust blowing around at night sifts through the open shutter of the telescope and settles down on the photographic plate, disturbing the precarious emulsion and making something that looks vaguely like a star. But sometimes something appears where it has never appeared before because it is slowly wandering across the sky and that single picture happened to catch it momentarily in one spot. In that case, an image the next night would find it again, only a little displaced from the previous night. I used the third picture as a final check. When the computer found a third object that looked as though it could be connected to the first two, it put that object on a list of potential new wanderers and moved on to the next spot in the sky. All of this takes, of course, about a millisecond. To process our two years’ worth of images took under two hours.
So after Kevin and Jean had spent all of those nights loading and developing plates, and I had spent a year programming the computer, and the computer had spent two hours processing all of the final data, I finally had a list of all of the potential new planets to look at. I had been sustained throughout this time by the thought of this moment. I was going to find a planet, and the solar system would never again be the same. When I first opened up the list on the computer screen and started scrolling down, I must have gasped. The list was 8,761 candidates long.
I knew that the computer would be overzealous in identifying potential planets; in fact, I had written the program to make sure that the computer was overzealous. I had decided early on that I would make the computer find everything even remotely possible, and I would look at each thing the computer picked out by eye to double-check it. But 8,761 objects to check by eye was going to take a long time.
I slowly began to go through the list. I would press a button on my computer, and on my screen three pictures would appear of the three nights of the same small region of the sky, with little arrows showing where the potential planet lay. I saw an amazing number of small glitches that had fooled the computer. Scratches on the photographic plates, of which there were many, would cause a star to disappear one night and so appear as if it were new the next. Anyone looking at the pictures could see that it was just a scratch, but to the computer it appeared as dark sky. Sometimes the light from a particularly bright star would get reflected around in the telescope perhaps dozens of times and give tiny apparent glints all across the sky. By eye, you would notice all of the glints and you’d see the proximity of the bright star, and you would quickly say, “Ah, that’s just a bright star making glints,” but to the computer it was a star never seen before.
The examination took months. On the computer screen, I had a “no,” a “maybe,” and a “YES!” button that I chose from after examining each of the pictures. Had it been a mechanical button instead of a virtual one on the computer screen, I would have worn the “no” button through. The “maybe” button got a little bit of action, too. Sometimes I would look at three pictures and find no obvious problems with what the computer had done, but I still wasn’t entirely convinced that what the computer had picked out was really there at all. The photographic emulsion was sometimes a little uneven, and the computer might have picked out a slightly brighter spot that really was just the sky. A tiny speck might appear that was possibly a faint star, but I was not quite convinced. In all of those not-entirely-sure cases, I would simply press “maybe.”
“YES!” was reserved for the no-questions-no-problems-definitely-really-there-moving-through-the-sky cases. Every day I would come in thinking that perhaps today was the day that I would finally push the “YES!” button. Every day I would spend hours staring at the computer screen, pushing “no,” and occasionally, very occasionally, “maybe.” But the “YES!” button remained untested. After going through the entire set of potential planets that the computer had picked out, I never once used the “YES!” Final score: “no,” 8,734; “maybe,” 27; “YES!” 0.
It was hard not to feel distressed. What if there really were no other planets out there? What if three years of photographing and computing and blinking came down to nothing at all? What if the big project designed to make my splash as a young professor at Caltech disappeared without a ripple? I had been telling everyone for three years now that I was looking for planets, that I was going to find planets. What if there were no planets?
I still had hope, though, in the twenty-seven maybes. I spent much of the fall of 2001 at Palomar Observatory trying to track them down. For a few dark nights every month, I would drive to the mountaintop, arriving early in the day to plan for the night and prepare the telescope, eating dinner before the sun was close to setting, packing up a bag full of truly awful snacks designed to keep me awake throughout the night
, and then heading for the control room of the 60-inch telescope.
This telescope had a modern digital camera, which meant that it was quite sensitive but that it covered a tiny area of sky. The nights were carefully choreographed so that I could spend the most time looking at the expected locations of the twenty-seven maybes. Because a full year had passed, they had moved quite a ways, and it was impossible to know precisely where they might be, so I would spend hours scouring large parts of the sky, taking a picture, and coming back to the same spot an hour later and taking another picture. I didn’t even bother writing a computer program for these; I would just look at the blinking images on my computer screen the second that they came down from the computer. All night, every night there, I would take a picture, move the telescope over, immediately start another picture, stare at the last picture while taking the current picture, and continue on until dawn. Then I would slowly and wearily walk the winding road the half mile back to the Monastery, often startling foxes or bobcats out for a dawn hunt. Around noon, I would wake up, have breakfast, and begin the day again.
During those first few months tracking down maybes, I felt excited when the sun went down.
Tonight is the night! I would think.
As the fall progressed, though, I was slowly becoming dejected.
I spent so much of my time at Palomar Observatory that fall that I didn’t have to think twice when I got a request to give a talk at the observatory to a group associated with Caltech. I was going to be there the night before anyway, so I figured I might as well stay one more night to give the talk. On my calendar I just wrote “talk to some group.” The group was to arrive by bus in the late afternoon, take a tour of the massive Hale Telescope, and eat dinner and hear my talk on the floor of the dome with the telescope perched overhead. It sounded fun. I like giving talks to groups like this.