REVIEW
THE GREAT COMET CRASH THE COLLISION OF
COMET
SHOEMAKER-LEVY 9 AND JUPITER
edited by John R. Spencer and Jacqueline Mitton
Cambridge University Press, Cambridge, 1995, 118 pp.
Color photographs and illustrations.
Hardcover, 0-521-48274-7. $24.95
On the warm, swampy Saturday afternoon of July 16, 1994, a handful of scientists with nothing terribly interesting to do were trying to look busy or wandering the nearly empty hallways of the Lunar and Planetary Institute in suburban Houston. Some of our summer intern students were also loitering about trying to be busy. In fact, we were all waiting. Around 4 p.m., a message was received via electronic mail. We read this simple message several times. After months of second-guessing and speculation, the first of some 21 fragments of disrupted Comet Shoemaker-Levy 9 were in; they had struck Jupiter. The resulting impact was visible from Earth after all, and was brighter in the infrared than Jupiter's large satellite Io. And the big fragments were yet to hit! Even without details or pictures, our initial realization that these events were producing major and obvious damage was electrifying. We returned late that evening from a futile attempt to witness light from the (fizzled) second comet fragment to see the amazing Hubble images of the first impact showing a domelike plume of hot gas rising over the limb of Jupiter.
SL9 imaged with the Isaac Newton Telescope on La Palma in the Canary Islands on May 15, 1994. The comet is 1.5 million kilometers long at this time. (M. Irwin, A. Fitzsimmons, and I. P. Williams.)
There is a special exhilaration for many humans that comes from witnessing such a powerful natural event for the first time, whether in the trenches doing the observing or on the sidelines as we in Houston were that week. I remembered similar emotions when we first saw the surface of Triton nearly five years earlier. Reading The Great Comet Crash, edited by John Spencer and Jacqueline Mitton, brought back vivid memories of that special week last July. The Great Comet Crash is a delight to read and leaf through. The text, by some of the astronomers and planetary scientists who participated, covers nearly every possible aspect of this event. Indeed, observing the comet and its fate united many branches of astronomy, geology, chemistry, and physics as few human endeavors can.
If I permit myself a quibble, it would be that times are given in Universal Time (UT), which not everyone knows requires five hours subtraction to convert to Eastern Standard Time (and which took us geologists half an hour to figure out). Also, the book does not fully benefit from the remarkable synthesis achieved during the IAU Colloquium on the SL9 impacts, held in Baltimore in May 1995, just after the book was completed. Several authors represented in the book come close to achieving this themselves, however. A reader may catch up with the colloquium results by reading articles in the October 1995 Sky and Telescope, which make nice companion pieces for this volume. This is by no means a flaw, because in the fast-paced world of astronomy (or most sciences), no book can be 100% up-to-date, and no doubt several more years will be required to fully reconstruct what occurred on Jupiter that fabulous week. Fortunately, little in this book will require revision on this basis.
The book itself is visually impressive. The black-and-white and especially the color illustrations are all reproduced with excellent detail and color balance, and it is obvious considerable care went into figure selection and preparation. Observational images are nicely supported by a number of useful diagrams or supplementary photographs.
But the real magic of this book is the story behind the pictures: Why comets are interesting, what was special about this comet, how observations were conducted, and some of the difficulties and adventures involved in obtaining these data are well described. The story of how the comet was discovered, including a foreword by Gene and Carolyn Shoemaker, as well as the process by which we determined its fate and set about planning to observe it, are all nicely told. Although not intended as a technical treatise (those will be published in the next few years), the scientific "impact" of this event is well explained in generally understandable terms.
The G impact produced the most dramatic impact scar yet seen, as shown in this HST image. It was taken between 09:19 and 09:25 UT, one and three-quarter hours after impact, when the site had rotated onto the visible disk. A dark ring, presumably some type of wave, spreads outward at 2000 kilometers per hour from the impact site, which is at one end of a dark streak that marks the approximate direction of the comet's entry into the atmosphere. Beyond the circular wave is a huge (Earth-sized) asymmetric halo. The much smaller site of the D impact, now 28 hours old, can be seen to the left of the E site. (Heidi Hammel and the HST Comet Team; additional processing by Robin Evans of JPL; courtesy John Trauger.)
The book concludes with two chapters discussing the comet crash and its aftermath as it affects our perceptions, both of the events themselves and what they might mean for our place in the solar system. (Two or three lines are missing from the final chapter and these are the only production flaws I encountered.) Even better, these stories are told by some of the major players and are all written in an easily accessible, occasionally humorous, but always meaty style. During the last 10 years we have begun to understand that the solar system is a vastly more dynamic place than the static, ordered family of regular planets visualized in many of the books I read growing up in the 1960s. The events of the week of July 16, 1994, demonstrate this in dramatic fashion, and this book nicely captures these and the events leading up to it with style.
--Paul M. Schenk
(Dr. Schenk is a staff scientist at LPI.)
Clementine Explores the Moon, compiled by Paul D. Spudis, is a 20-slide set that features an overview of the Clementine Mission, also known as the Deep Space Program Science Experiment, as well as images and image products from the data collected during the spring of 1994. Clementine began the work of building the first truly global digital image model of the Moon. With its ultraviolet-visible and near-infrared camera, the spacecraft obtained 11-color multispectral data of virtually the entire Moon. Compiled by the Deputy Science Team Leader for the Clementine Mission, the set includes a south pole mosaic, nearside and farside albedo maps, global color data, global topography, global iron data, a full- Earth mosaic, and more. $15.00 from LPI; see Order Form in this Bulletin.