BOOKS

Comet Halley: a Unique Scientific Lab Reviewed by Michael F. A'Hearn

The current reappearance of Hal-ley's Comet has led to a plethora of commercial activity, frequently re­ferred to as Halley hype. Available now on the market because of it are new telescopes, T-shirts, pins, news­letters, hotlines, bumper stickers, silver spoons, and a host of other souvenirs. Naturally, too, a wealth of books have been published re­cently about Edmund Halley and his comet.

Virtually all this commercial ac­tivity is aimed at a very popular lev­el—for the person in the street who knows of no comet other than Hal-ley's. Astronomers tend to have mixed feelings about such commer­cialism. Some are offended and find it tawdry and distracting from the real scientific significance of com­ets; others are of the opinion that the commercial activities generate public interest, which ultimately gets transformed into support for scientific studies.

But why does this particular com­et attract so much attention? Of the 15 to 25 comets that are discovered or reappear annually, most never become bright enough to be seen with the unaided eye. Even though faint comets are important scientifi­cally, that the average person can­not hope to see them makes them relatively less interesting than a comet such as Halley's. Every five to 10 years, however, a truly spectacu­lar comet appears, one that is far more impressive to the unaided eye than Halley's Comet will ever be during its current orbit. The most recent of these was Comet West, a magnificent sight in the early morn­ing hours during March 1976, yet this comet is totally unknown to most people other than astrono­mers.

The difference is that Halley's is the only periodic comet that can be seen during every return and bright enough to be spectacular during geometrically favorable returns. All

26 January 6, 1986 C&EN

The reappearance of Halley's Comet offers an opportunity for studying

the solar system and

basic physical processes

"Comet Halley: Once in a Life­time" by Mark Littmann and Don­ald K. Yeomans, American Chemi­cal Society, 1155—Sixteenth St., N.W., Washington, D.C. 20036, 1985,176 pages, $19.95 (hardcover), $12.95 (paperback)

Michael F. A'Hearn, professor and act­ing director of astronomy at the Univer­sity of Maryland, has done research on comets for more than 10 years and now is involved with several observational programs on Comet Halley

of the other bright comets are non-periodic (or, at least, have orbital pe­riods longer than recorded history) and were discovered only weeks to months before they became spectac­ular. Halley's Comet, on the other hand, can be predicted in advance and has been known for so long that it has a rich history. There are more anecdotes told about it than about any other comet, such as its associa­tion with Josephus, Attila, William the Conqueror, Pope Calixtus III, Agrippa, and Mark Twain.

These stories fascinate many peo­ple who would not otherwise think of reading about comets. Nearly all the books recently written about Halley's Comet are aimed at this large audience, the people who want to hear the stories and see the comet for themselves, rather than at scientifically oriented readers.

This might lead one to ask wheth­er this comet is of more scientific interest than other comets. To an­

swer this question, it is essential to understand both the nature of com­ets generally and the reasons astron­omers study them. These points are discussed in virtually none of the recent books about Halley's Comet.

Mark Littmann and Donald K. Yeomans, like the authors of the other books, have targeted "Comet Halley: Once in a Lifetime" at a gen­eral audience interested mainly in the stories and in what to look for. They present a lot of fascinating his­torical detail of which I was not pre­viously aware. But Littmann, sci­ence communicator for NASA's Space Telescope Science Institute at Johns Hopkins University, and Yeo­mans, an astronomer at the Jet Pro­pulsion Laboratory, also present more scientific background than ex­ists in any of the half-dozen other books about the comet that I have looked at with any care. (There are, of course, many books on the comet that I have not had time to examine closely.)

Several reasons exist for studying comets. They are excellent laborato­ries for some basic physical process­es, particularly in plasma physics: ionization mechanisms, accelera­tion mechanisms, instabilities, the interaction between moving plas­mas, magnetic reconnection, and even the basic properties of the plasma—known as the solar wind— streaming out from the sun. They also may help answer several basic questions about how things got to be the way they are today. Comets may have played a major role in de­termining the variety of living spe­cies now present on Earth, a role that will be clarified by further studies of their dynamics. They also are generally thought to consist of primordial, unprocessed material preserved since the solar system formed. Studies of the chemical and physical nature of the cometary nu­cleus could place critical constraints on our models for the formation of the solar system. Dead comets also may be the source of many of to-

day's Earth-approaching asteroids, a possibility that requires further studies of the dynamics as well as of the physical nature of both asteroids and comets.

The basic scientific facts relevant to answering these important ques­tions are laid out in "Comet Halley: Once in a Lifetime," although the potential of future or even current studies is barely hinted at, except for a discussion of comets as clues to the origin of the solar system. In my mind, this is the most important role for comets in solar system studies, but I would have liked some discus­sion of their other roles. The aver­age reader of C&EN, with perhaps no knowledge of comets but a strong technical background, al­most certainly will finish the book with unanswered questions. At some level this is good, but a more detailed discussion of the role of comets might have elevated these questions to a higher level.

The book itself is chopped up, with single pages (or pairs of facing pages) that present straight, techni­cal details scattered within the chapters, each of which otherwise follows a single, clear line. Al­though setting some of the material apart allows a nontechnical reader to get through the book more easily, it also makes the book somewhat harder to read for those with a strong technical background. And it becomes very inconvenient to look up certain ideas without constantly referring to the index.

Perhaps one of the most surpris­ing omissions from "Comet Halley: Once in a Lifetime," particularly in view of the direct involvement by Yeomans in the planned comet fly-by missions, is the absence from the chapter on these space missions of any discussion of the types of mea­surements that will be made from the spacecraft. It seems to me that even a general reader might want to know something about what the spacecraft will measure that we don't already know.

My overall impression is that the book is easily the best and most comprehensive of the many recent books on Halley's Comet that I have read. But it still has a number of de­fects that may bother a technically oriented reader. Fortunately, such a

reader will be considerably aided by what appears to be a very well-bal­anced list of references that can be used to fill in many of the missing ideas. On the other hand, looking up specific information is compli­cated both by the separation be­tween popular and technical materi­al and by an index in which every reference beyond page 138 is incor­rect.

In view of the many reasons for studying comets, does anything make Halley's Comet special? Is there any scientific importance to Halley's being the brightest of the periodic comets? In fact, there is. Many studies can be carried out only on a bright, active comet. Earth-based observers are con­strained by the number of photons arriving from the comet, a factor over which they have no control. Despite recent technological ad­vances, for example, it is still not possible to measure relatively weak spectral features in any but the brightest comets. Similarly, it is not possible to study the range of plas­ma phenomena in any but very ac­tive comets. Even measurements from space probes require a bright comet unless the spacecraft can ren­dezvous with the comet and per­

form measurements with very long integration times. Spacecraft such as those headed toward Halley's Com­et must make their measurements in a very short time and therefore re­quire an active comet with high densities of gas and dust.

Although these measurements could, in principle, be carried out on any bright comet, many of them re­quire so much advance planning that it is not practical to carry them out on any but a periodic comet. It is out of the question, for example, to build spacecraft to fly by a comet and then leave them sitting on a shelf until a comet bright enough is discovered, in part because it is im­possible at present to predict the precise orbit of such a comet.

Even some ground-based mea­surements demand similar advance planning, particularly programs that require many different tele­scopes for simultaneous ultraviolet, optical, infrared, and radio studies or programs that require observa­tories at many longitudes to provide continuous coverage in time. This combination of a need for advance planning and a need for a bright comet makes Halley's Comet unique—the only bright, active pe­riodic comet. D

Handbook of Hazard Communication and OSHA Requirements. George G. Lowry, Robert C. Lowry. 148 pages. Lewis Publish­ers, 121 South Main St., Chelsea, Mich. 48118. 1985. $24.95.

Handbook of Monoclonal Antibodies. Sol-dano Ferrone, Manfred P. Dietrich, editors, xxii + 477 pages. Noyes Publication, Mill Rd. at Grand Ave., Park Ridge, N.Y. 07656. 1985. $72.

Heterocyclic Chemistry. Vol. 4. H. Sus-chitzky et al. xx + 466 pages. Royal Society of Chemistry, Distribution Centre, Blackhorse Rd., Letchworth, Herts., SG6 1HN, England. 1985. $138.

Higher Excited States of Polyatomic Mole­cules. Vol. 3. Melvin B. Robin, xv + 465 pages. Academic Press, 111 Fifth Ave., New York, N.Y. 10003. 1985. $49.50.

Oils, Lubricants, and Petroleum Products: Characterization by Infrared Spectra. John P. Coates, Lynn C. Setti. xxvi + 2^4 pages. Marcel Dekker Inc., 270 Madison Ave., New York, N.Y. 10016. 1985. $145.

Organophosphorus Chemistry. Vol. 15. D. W. Hutchinson et al. xiv + 335 pages. Royal Society of Chemistry, Distribution Centre, Blackhorse Rd., Letchworth, Herts., SG6 1HN, England. 1985. $122.

Plastics for Electronics. Martin T. Goosey, editor, ix + 380 pages. Elsevier Science Pub­lishing Co., 52 Vanderbilt Ave., New York, N.Y. 10017. 1985. $67.50.

Polymer Blends and Mixtures. D. J. Walsh, J. S. Higgins, A. Maconnachie, editors, ix + 469 pages. Kluwer Academic, 190 Old Derby St., Hingham, Mass. 02043. 1985. $59.50.

Polyurethane Handbook. Gunter Oertel, editor, xxiii + 626 pages. Macmillan Publish­ing Co., 866 Third Ave., New York, N.Y. 10022.1985. $128.

Principles of Instrumental Analysis. 3rd Ed. Douglas A. Skoog. xii + 879 pages. CBS Col­lege Publishing, 383 Madison Ave., New York, N.Y. 10017. 1985. $43.95.

Processing, Structure, and Properties of Block Copolymers. M. J. Folkes, editor, χ +

January 6, 1986 C&EN 27

Books

212 pages. Elsevier Science Publishing Co., 52 Vanderbilt Ave., New York, N.Y. 10017. 1985. $45.

Pseudopotential Theory of Atoms and Mol­ecules. Levente Szasz. xi + 309 pages. John Wiley & Sons Inc., 605 Third Ave., New York, N.Y. 10016. 1985. $54.95.

Reactivity of Solids. Parts A&B. Pierre Bar­ret, Louis-Claude Dufour. xxix + 1148 pages/2-vol. set. Elsevier Science Publishing Co., 52 Vanderbilt Ave., New York, N.Y. 10017. 1985. $194.50/set.

Scaleup of Chemical Processes. Attilio Bisio, Robert L. Kabel. xviii + 699 pages. John Wi­ley & Sons Inc., 605 Third Ave., New York, N.Y. 10016. 1985. $69.95.

Solid State Chemical Sensors. Jin Janata, Robert J. Huber, editors, ix + 211 pages. Aca­demic Press, 111 Fifth Ave., New York, N.Y. 10003. 1985. $49.

Solvent Extraction and Ion Exchange in the Nuclear Fuel Cycle. D. H. Logsdail, A. L. Mills, editors, 223 pages. John Wiley & Sons Inc., 605 Third Ave., New York, N.Y. 10016. 1985. $62.95.

Spectrometric Techniques. Vol. 4. George A. Vanasse, editor, xii -I- 262 pages. Academic Press, 111 Fifth Ave., New York, N.Y. 10003. 1985. $75.50.

Spectroscopic Properties of Inorganic and Organometallic Compounds. Vol. 17. G. Da­vidson et al. 395 pages. Royal Society of Chemistry, Distribution Centre, Blackhorse Rd., Letch worth, Herts., SG6 1HN, England. 1985. $138.

Spray Drying Handbook. 4th Ed. K. Masters xiv + 696 pages. John Wiley & Sons Inc., 605 Third Ave., New York, N.Y. 1985. $79.95.

Stiff Computation. Richard C. Aiken, editor, xiv + 462 pages. Oxford University Press, 200 Madison Ave., New York, N.Y. 10016. 1985. $75.

Structural and Resonance Techniques in Biological Research. Denis L. Rousseau, edi­tor, xi + 476 pages. Academic Press, 111 Fifth Ave., New York, N.Y. 10003. 1984. $69.

Structural Chemistry of Silicates. Friedrich Liebau. xii + 347 pages. Springer-Verlag New York, 175 Fifth Ave., New York, N.Y. 10010. 1985. $57.

Structure-Property Relationships in Poly­mers. Raymond B. Seymour, Charles E. Car-raher Jr. xiii + 232 pages. Plenum Press, 233 Spring St., New York, N.Y. 10013. 1984. $22.50.

The Subatomic Monster. Isaac Asimov. 213 pages. Doubleday & Co., 245 Park Ave., New York, N.Y. 10167. 1985. $16.95.

Surface and Colloid Science. Vol. 13, Egon Matijevic, Robert J. Good, editors, xiii + 297 pages. Plenum Press, 233 Spring St., New York, N.Y. 10013. 1984. $45.

Textile Identification, Conservation, and Preservation. Rosalie Rosso King, xvi + 361 pages. Noyes Publications, Mill Rd. at Grand Ave., Park Ridge, N.J. 07656. 1985. $39.

Thin Films and Interfaces II. J. E. E. Baglin, D. R. Campbell, W. K. Chu, editors, xv + 684 pages. Elsevier Science Publishing Co., 52 Vanderbilt Ave., New York, N.Y. 10017.1984. $85.

Thorium Dioxide: Properties and Nuclear Applications. J. Belle, R. M. Berman, editors, xiii + 573 pages. National Technical Informa­tion Service, U.S. Department of Commerce, 5285 Port Royal Rd., Springfield, Va. 22161. 1984. $41.50.

To Engineer Is Human: The Role of Failure in Successful Design. Henry Petroski. xiii +

Ammonia Plant Safety and Related Facili­ties. Vol. 25. 208 pages. American Institute of Chemical Engineers, 345 East 47th St., New York, N,Y. 10017. 1985. $18 AIChE members; $36 others.

Atoms of the Living Flame: An Odyssey into Ethics and the Physical Chemistry of Free Will. George Prescott Scott, Ilya Prigo-gine. xiii -I- 375 pages. University Press of America. 4720 Boston Way, Lanham, Md. 20706. 1985. $29 hardback, $15.75 paperback.

Carbon-14 in the Environment, vi + 108 pages. National Council on Radiation Protec­tion & Measurement, 7910 Woodmont Ave., Bethesda, Md. 20814.1985. $12.

Chemical Demonstrations: A Sourcebook for Teachers. Lee R. Summerlin, James L. Ealy Jr. 190 pages. American Chemical Soci­ety, 1155—16th St., N. W. Washington, D.C. 20036. 1985. $19.95.

Chemical Engineering Faculties 1985-1986. Vol. 34. John G. Ekerdt, editor, ix + 255 pages. Publication Sales Dept., American Institute of Chemical Engineers, 345 East 47th St., New York, N.Y. 10017. 1985. $20 AIChE members; $40 others.

Chemical Principles in the Laboratory. 4th Ed. Emil J. Slowinski, Wayne C. Wolsey, Wil-

247 pages. St. Martin's Press, 175 Fifth Ave., New York, N.Y. 10010. 1985. $16.95.

Transition Metal Chemistry. Vol. 9, Gordon A. Melson, Brian N. Figgis, editors, vi + 312 pages. Marcel Dekker Inc., 270 Madison Ave., New York, N.Y. 10016. 1985. $65.

Transmission. Vol. 2, Book T-2, Compressor Station Operations, xv + 286 pages. Ameri­can Gas Association, 1515 Wilson Blvd., Ar­lington, Va. 22209. 1985. $25 AGA members; $30 nonmembers.

Water Treatment Principles and Design. James M. Montgomery, xii + 696 pages. John Wiley & Sons Inc., 605 Third Ave., New York, N.Y. 1985. $49.95.

Water Treatment Specification Manual. Frank Rosa, χ + 207 pages. McGraw-Hill Book Co., 1221 Ave. of the Americas, New York, N.Y. 10020. 1985. $35.

What Went Wrong? Case Histories of Pro­cess Plant Disasters. Trevor A. Kletz. xix + 204 pages. Gulf Publishing Co., P.O. Box 2608,3301 Allen Pkwy., Houston, Tex. 77001. 1985. $39.95.

liam L. Masterton. xi + 335 pages. CBS Col­lege Publishing, 383 Madison Ave., New York, N.Y. 10017. 1985. $21.95.

Consider a Spherical Cow: A Course in En­vironmental Problem Solving. John Harte. xvi + 283 pages. William Kaufmann Inc., 95 First St., Los Altos, Calif. 94022. 1985. $24.95 hardback; $12.95 paperback.

The Elements of Graphing Data. William S. Cleveland, xii + 323 pages. Wadsworth Ad­vanced Books & Software, 555 Abrego St., Monterey, Calif. 93940. 1985. $27.95 hard­back; $18.95 paperback.

Experimental Results from the Design In­stitute for Physical Property Data. 1: Phase Equilibria. Montford S. Benson, David Zud-kevitch, editors, viii + 164 pages. AIChE, 345 East 47th St., New York, N.Y. 10017.1985. $20 members; $40 others.

Heat Transfer-Denver 1985. Nayeem M. Farukhi, editor. 281 pages. AIChE, 345 East 47th St., New York, N.Y. 1985. $25 AIChE members; $40 others.

Separation of Heavy Metals and Other Trace Contaminants. Robert William Peters, B. Mo Kim, editors. 203 pages. American In­stitute of Chemical Engineers, 345 East 47th St., New York, N.Y. 10017. 1985. $17 AIChE members; $35 others.

28 January 6, 1986 C&EN

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