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Shoemaker by Levy:
The Man Who Made an Impact
David H. Levy

Book Description | Reviews | Table of Contents

COPYRIGHT NOTICE: Published by Princeton University Press and copyrighted, © 2000, by Princeton University Press. All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means (including photocopying, recording, or information storage and retrieval) without permission in writing from the publisher, except for reading and browsing via the World Wide Web. Users are not permitted to mount this file on any network servers. Follow links for Class Use and other Permissions. For more information, send e-mail to permissions@press.princeton.edu

Chapter 1

OF BONDING AND DISCOVERY: 1993

Strange, is it not? that of the myriads who
Before us pass'd the door of Darkness through,
   Not one returns to tell us of the Road,
Which to discover we must travel too.

--Fitzgerald, Rubaiyat of Omar Khayyam

Do you three ever have a comet!" said Jim Scotti from the control room of his telescope. Shielded from the cold night atop a mountain in southern Arizona, Jim was looking at his monitor screen and beholding the strangest sight he had ever seen in the night sky—a train of several comets, each one coupled to the next by a thick layer of dust. Gene and Carolyn Shoemaker and I were in a room beneath our telescope, four hundred miles to the west on Palomar Mountain, also huddled against the wind and snow outdoors. We would not be opening the telescope this night, but thanks to Jim's confirmation, our cometary prey was already in the net.

    Two nights earlier, the evening of March 23, 1993, Gene; his wife, Carolyn; and I were at Palomar Mountain Observatory, working on his Palomar Asteroid and Comet Survey. We were taking photographs of the sky—as much of it as possible each month—in search of comets and asteroids. Gene's goal was to determine the rate of impacts in our corner of the solar system.

    Gene had a dream. With all the craters, and crater-making objects he had seen, he wanted to cap his career by actually witnessing an impact, perhaps on some remote desert area in Australia, and then rush out and map the result. He talked about that dream often, and even might have been thinking of it on that evening of March 23, when a row of clouds put a stop to our observing. We walked outside, together with Philippe Bendjoya, an astronomer from France who was checking out our operation that month.

    "I think we should keep on observing," I said, conscious that in an El Niño year, the onset of clouds likely meant that we would not get to use the telescope for several days.

    Gene's reply had a financial twist to it. "There's David, ever the optimist!" he began. "But really, we spend some four dollars each time we slap a piece of film into that telescope. In the course of a year that might amount to some eight thousand dollars just on film. David, we're just going to have to wait this one out."

    As we stood there silently, gazing up at what stars could be seen through the gathering clouds, I remembered the rude surprise we had received the evening before: we had to stop observing because our film had gone bad. Someone had opened our box of carefully prepared emulsion, exposing its contents to light. The films had been stored one on top of the next, so the uppermost films, which were completely ruined, served somewhat to protect the lower ones. We limped through the rest of that night with these damaged films—their centers were usable, but their edges were struck with light.

    Our second night began on a better note. Armed with a fresh supply of film, we began work and kept on until those clouds rolled in. And here we were, waiting out what appeared to be the leading edge of another storm. I thought about last night's damaged films, and of Gene's financial argument, and had an idea.

    "Gene, do we have any damaged films left over from last night?"

    "Yes, I saved them for focus tests."

    "Those films don't cost us anything," I continued. "If we use them, we have nothing to waste but our time."

    We looked at the sky, then at each other. "Let's do it!" Gene bellowed. We rushed up to the dome. Gene gave me the filmholder, which I locked into place in the belly of the eighteen-inch Schmidt camera. He read me two coordinates, the right ascension and the declination—the sky's extension of longitude and latitude—and I positioned the telescope. I looked through the eyepiece to locate the star on which I would guide the eight-minute exposure and was really surprised to see a bright glow. I looked hard and found the guide star, barely visible amidst the glow. I looked up and saw the problem at once: Jupiter, the solar system's largest planet, was very close to the center of where I had pointed the telescope.

    I suggested to Gene that because the partly clouded sky was so bright from Jupiter's glare, maybe we should move to another field of sky. But since this was the next field on our program, we decided to stick with it. "If you can't see the guide star at all," he said, "then we'll go somewhere else."

    "No," I answered, "the star is faint, but I can follow it. We can stay here. I'm ready to go!"

    Gene then waited until the clock's second hand was about to reach a quarter minute, and then began to count: "Five, four, three, two, one, Open!"


How to Learn a Lot in Four Minutes


Pulling on a lever, I heard a soft squeaking sound as the telescope's two metal shutters swung open. The exposure was in progress. Gene went downstairs to load another sheet of six-inch diameter circular film into its holder, then returned. For about three minutes, Gene could relax as I guided the exposure. We chatted casually.

    These three-or four-minute chats were extremely useful times for us. While I can't recall what we talked about during this particular exposure, these times were golden opportunities to get caught up on news, to express our opinions about various subjects, or just to enjoy the night. Conversation was important during this time, especially as the night wore on and we grew tired. We also had a cassette recorder that played classical, jazz, country, or Australian music.

    Sometimes—especially late at night—the conversation would be just plain fun. When Carolyn and I observed together we got downright nonsensical—the humor kept us going and made the long nights pass quickly. On our very first observing run together, Carolyn and I were at the telescope while Gene was in Pasadena as part of the Voyager 2 imaging team looking at images coming in from the spacecraft as it swung by Neptune's moon Triton. Carolyn had prepared two boxes of films for use that night—using a film cutter to shape the films into six-inch circles, she then connected the boxes to a supply of "forming gas" of 92 percent nitrogen and 8 percent hydrogen, and placed them into an oven. In six hours, the films were hypersensitized—which meant that with our Kodak 4415 Technical Pan film, the hypersensitizing process increased the sensitivity of films to light by a factor of nine. Gene called the process "baking the cookies."

    On that second night together, our program was proceeding faster than expected. Thinking that our supply of films was running low, Carolyn mused that we might actually have to stop before dawn if we ran out of hypersensitized film. So as Carolyn guided an exposure, I went downstairs, replaced the film, and retraced the twelve steps to the observatory dome. "Carolyn," I said plaintively, "I checked. We're completely out of film."

    "I see," she replied.

    "The film you have is the last one."

    "Hmmm."

    "But I think I found a way to use more film."

    "What's that?"

    "Two minutes to go in this exposure, Carolyn. Well, you know I've been using hypered 35mm film in my own camera ..."

    "Yes?"

    "Well, I brought some. What I did was, I took four strips of the film, crunched it into the filmholder, and like that!"

    Carolyn looked really puzzled. "How do I tell this nice man," she later admitted thinking, "who has come all this way to be a part of the program, that his idea is just plain dumb?"

    Instead she said, "But David, when we develop these strips of film, how shall we know which one goes where?"

    "Forty-five seconds, Carolyn," I noted the time remaining on the current exposure. "Well, we can put them together with Scotch tape and then I'd compare them with a nice star Atlas and we could figure it out." Really concerned now, Carolyn looked up from her eyepiece and noticed my wide grin.

    "David! I think I've just been had!"

    "Twenty seconds!"

    We laughed about that one for years. It was the first of many moments of genuine laughter between us that helped make these moments so special. The best jokes came late at night. On another night I rushed up the twelve stairs to the dome to present Gene with a new film, only to realize that there was still a few minutes left of the exposure. "You're in a hurry!" Gene said, his nimble fingers pressing the buttons that guided the telescope. Since this particular exposure was in the eastern half of the sky, where the telescope tended to wander off its guide star, Gene was pressing the east and west guiding buttons every few seconds. With each press the telescope made a ssssst sound as it raced to catch up with the Earth's rotation, and a lower pitched bzzzt! if it needed to slow down.

    "Well, maybe the night will go faster if I hurry," I admitted, quite out of breath.

    "Well, I don't know. Did you hear about the old bull and the young bull?" Sssst, sssst.

    I admitted that I hadn't.

    "Well," Bzzzzt! "Damn! Wrong way." Ssssssssssssssssst. "Two bulls were standing at the top of a hill, an old bull and a young one." Ssssssst. "They were watching a herd of cows at the bottom of the hill, and the young bull was strutting around." Sssssst. Bzzzzt! Bzzzzzzt! "`I wanna charge down the hill and make love to the first cow I run into!"' Bzzzzt! Bzzzzt!

    "The old bull looked out over the herd. `Well, you can do that. I will walk downhill slowly and sagely.'" Ssssssssst! "`And then I'll get the whole damn herd!' Damn!" Sssssssssssssssssssst!

    "One minute, Gene!"

    Usually our conversations were more serious, like the time I asked Gene what he thought of Frank Drake's famous equation on how common life is in our galaxy. The equation reads


N = N* fp ne fl fi fc fL


where N is the number of intelligent civilizations in our galaxy capable of communicating with us. N is based on numbers and fractions that express the number of stars in our galaxy, the fraction of those stars with planets, the number of those planets that are Earth-like, the fraction where life took hold, the fraction where life evolved to intelligence, the fraction where life evolved to technological communication, and finally, the fraction of time a civilization is likely to last. The traditional Ns vary widely; optimists suggest several hundred thousand; pessimists say one.

    I found that while Gene did think that N is more than one, he feared that it is very low. He explained that the equation leaves out one important factor that might reduce the value of N. A solar system must have at least one Jupiter-sized planet. "Jupiter works like a vacuum cleaner," he said. "The planet's gravity is so strong that it rids the solar system of billions of comets." These comets, he continued, are affected by Jupiter's gravity and are flung out of the solar system, or, in rarer cases, actually collide with the giant planet. Without a Jupiter in the system, comets would continue to rain down on Earth-sized planets, just as they did in our system when it was young. Without Jupiter, our Earth would still be a target for ten kilometer-diameter comet strikes at the rate of one per century instead of the present comfortable rate of one each hundred million years.

    "Thirty seconds!" Gene interrupted his train of thought to let me know to get ready to close the shutter. With time running out for the exposure, I asked Gene how serious this consideration was. "Pretty serious," he answered. I think it brings the value of N pretty close to one. I don't think we are alone, but I do think that the development of advanced life forms is pretty rare in our galaxy.

    In this way, I learned an awful lot of planetary geology in three- or four-minute segments.

    Out of little stories like these were wonderful memories built. I learned more about geology, impacts, and the character of Gene and Carolyn during these short segments—all while the telescope patiently gathering photons of stars, galaxies, asteroids, and comets—than at any other time during our relationship. And Gene, Carolyn, and I never let the stories overstretch the exposures. Whatever jokes, stories, educational anecdotes, or other conversation was happening on this night of March 23, 1993, the time for the Jupiter exposure finally ran out as Gene called out "five, four, three, two, one, close!"


The Night Groans On


The sky clouded over again as we struggled through the next two images. Finally we had to stop. I went outdoors several times to check on the sky. We worried that if we did not begin the "bottom half of the inning" soon, we might have to scrap the set. The way our films work for comet discovery is that they detect the motion of a comet or an asteroid; it is in different places from one film to the next. When Carolyn stereoscopically studies a pair of films that are identical in every regard except that they were taken some forty-five minutes apart, she can see a moving object appear to "float" on top of the background of stars. What an elegant way to search for new worlds!

    In order to see these new worlds, we needed two films of every area, and ideally the films should not be spaced shorter than forty minutes apart, or longer than about an hour. As we waited for the clouds, an hour passed from the start of the first exposure, then ninety minutes. Despairing, I went outside one more time. There appeared to be a small hole in the clouds, moving eastward. With a little luck, I thought, it would pass the Jupiter area and stay clear long enough for me to just get in the second exposure. Gene and I ran up the stairs, loaded the film, and reset the telescope. For a while I couldn't see the guide star at all, but after a few more minutes the break in the clouds reached the Jupiter region and the guide star just slightly appeared. I began the exposure and kept going for eight minutes. The clouds closed over again just before the end of the exposure. We struggled through the rest of that night, and on the following night we took a few more exposures before the heavier clouds moved in, shutting off our observing run for the next few nights.


A Unique Discovery


Even though we were not accomplishing much because of the weather, we were thoroughly enjoying each other's company this run. Philippe Bendjoya, one of the most delightful people we've ever shared the dome with, was interested in watching what we were doing, yet each cloudy evening he would assist me with my faltering French. Our late night dialogues covered politics, religion, even astronomy—and were all en Français. So by the afternoon of March 25, we were a quiet but satisfied group, saddened only because the weather was keeping us from observing. Carolyn even looked up from her scanning, saying plaintively, "You know, I used to be a person who found comets."

    "Used to be?" Gene asked.

    On a few occasions, when she said those words, Carolyn would find a comet. She completed her scanning of the first night's films with no luck. It was time for Gene and me to head over to the nearby sixty-inch telescope dome, which housed the oven for hypersensitizing. By now the storm was raging, with high winds and light snow. We knew that there would be no observing that night, but we were going through the motions of hypering the film and preparing the night's observing plan, just in case.

    We returned to our eighteen-inch telescope dome. With observing unlikely that night, 4 P.M. was the slow part of the afternoon. I continued working on my cloudy-day activity of writing a book called The Quest for Comets. Gene was catching up on his reading of a paper being prepared for publication. Carolyn was scanning the Jupiter field. Somewhat tired from the previous night's observing, Philippe was napping in the car.

    Suddenly Carolyn stopped the steady movement of her stereomicroscope. She had just skidded past a fuzzy something that looked a bit like the fuzzy appearance of a distant galaxy. Was it floating? She backed up, increased the magnification, sat straight in her chair, and peered intently into the eyepieces. After a few seconds she looked at us. "I don't know what I've got, but it looks like a squashed comet."

    As Gene walked over to look, Carolyn smiled at me. Was she being humorous? After all, she had just defined herself as a person who used to find comets! "No," she said, "there's something strange out there."

    Gene studied the images carefully, then looked at me with the most bewildered look I've ever seen on the man. Now it was my turn. I saw two discrete images of what really did look like a comet someone had stepped on. At the center was a bar of fuzzy, cometary light, appearing dark of course, since we were using the original negative films. Stretching to the north of the bar were clearly defined cometary tails. "It's got to be a comet," I called out, "look at those tails!" Then I noticed the pencil-thin lines extending along either side of the bar.

    Sensing the excitement, Philippe appeared. We told him what had happened and he, too, looked at this unique object. I prepared an e-mail message about the comet; then Gene and I logged into the computer service of the International Astronomical Union's Central Bureau for Astronomical Telegrams. It was time to report our discovery to the center's director, Brian Marsden. After our initial message was cut off in midtransmission, we wrote this letter:


We got cut off on our last message to you (the one we logged directly to your computer service) so we are resending with more details.


The strange comet is located as follows:


1993 03 24.35503 12 26.7 (2000.0) - 04 04 M = 14


[The numbers refer to the year, month, and date to five decimal places; the right ascension and declination in coordinates standardized to the year 2000; and the brightness of the comet at magnitude 14.]

The motion is west-northwest (not southeast as in the previous message) at about 7 arcminutes per day. The image is most unusual in that it appears as a dense, linear bar very close to I arcminute long, oriented roughly east-west. No central condensation [a thickening of the comet toward its center] is observable in either of the two images. A fainter, wispy "tail" extends north of the bar and to the west. Either we have captured a most unusual eruption on the comet or we are looking at a dense tail edge-on.

Right now we are sitting in the middle of a cloud with no hope of observing tonight, and we had very poor observing last night. Observers are Eugene and Carolyn Shoemaker, David Levy, and Philippe Bendjoya."


    After we sent this message, we left the observatory to head for the house we rented for the observing runs. During the drive back Gene suggested a possible scenario for the comet's appearance. The comet is close to Jupiter in the sky. Suppose the comet was physically near it in space, close enough to have been tidally disrupted by the planet? Maybe the comet's elongated appearance indicated that it had split apart. Like many of Gene's hunches, this one turned out to be spectacularly correct.


Confirming the Discovery


After our dinner break we returned to the observatory. The sky was hopelessly cloudy, so there was no chance of rephotographing the new comet ourselves. I called Jim Scotti, a close friend who was that night observing with the Spacewatch camera on Kitt Peak, west of Tucson, as part of a search for asteroids and comets, and told him that we had an unusual comet not far from Jupiter. When I gave him the two positions, he quickly realized that the comet was also moving in the same direction and velocity as Jupiter. He suggested that our "comet" was nothing more than a reflection of Jupiter's light in the telescope! He did agree, however, to try to get an image for us.

    Concerned, Gene quickly took a straight-edge and extended the line that the comet drew in space toward Jupiter. The line passed just south of the planet. If it had been a reflection, Gene reasoned, the line should have gone straight to the big overexposed splotch that was Jupiter. In the meantime, Gene and I went over to the dome of the forty-eight-inch Schmidt, which housed the device we used to measure accurate positions of our comet. Jean Mueller, our friend who works the forty-eight-inch telescope for the Second Palomar Sky Survey, greeted us there and helped us measure the comet's discovery images. About two hours later we returned to the eighteen-inch.

    Because the night was stormy, we brought our music downstairs; it was playing Beethoven's first symphony. It was time to call Jim. He picked up the phone and began to clear his throat. "Jim," I said, "Are you all right!"

    "Oh, yes!" he got himself to answer, shakily.

    "Do we have a comet?" Right at this moment, the opening chords of the final movement of Beethoven's first began.

    "Do you three ever have a comet!" I repeated Jim's words as he explained that his telescope was showing at least several nuclei, all connected by dust, five tails, and two long pencil-thin lines (that turned out to be trains of dust) on either side of the nuclei—all as the music lurched into the movement's opening crescendo of what we renamed Beethoven's Comet Symphony. Later, Jim reported to the Central Bureau for Astronomical Telegrams:


It is indeed a unique object, different from any cometary form I have yet witnessed. In general, it has the appearance of a string of nuclear fragments spread out along the orbit with tails extending from the entire nuclear train as well as what looks like a sheet of debris spread out in the orbit plane in both directions. The southern boundary is very sharp while the northern boundary spreads out away from the debris trails.


    At Palomar, the energy in that little room was extraordinary. We knew that our program had uncovered the most unusual-looking comet in history. Comets typically sport heads and tails; this one was a line consisting of several heads and tails. We were walking on the ceiling. In Gene's exhilaration that night, he had no idea that this comet's performance was only the overture, and that the comet's four-billion-year-long journey through the solar system was about to end in the most spectacular collision ever seen in the solar system. The coming event would grab Gene's lifework, confirm its significance, and blaze it over the front pages of the world.

Copyright © 2000 Princeton University Press. All rights reserved.

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