Example of a checklist for the first day of a major meeting with parallel sessions.

Monday, May 15, 1989

1. (A) Morning

1. (1) Four slide projectors for use, two spares; four extension cords; two spare bulbs.

2. (2) Four supports for projectors.

3. (3) Four wireless pointers, two spares.

4. (4) Four screens of adequate size (check rooms).

5. (5) Four wireless microphones, two spares.

6. (6) Four podiums with lights (plus spare bulbs).

7. (7) Reserved seats (front row) for speakers and special guests of the opening ceremony.

1. (B) Afternoon

1. (1) Five slide projectors for use, one spare; five extension cords; two spare bulbs.

2. (2) Five supports for projectors.

3. (3) Five pointers for use, one spare.

4. (4) Five screens (check fifth screen for adequate size).

5. (5) Two overhead projectors (for Colloquia).

6. (6) One hundred poster boards with running numbers in upper right corner.

7. (7) 9000 push pins for posters.

8. (8) Five wireless microphones, one spare.

9. (9) Five podiums with lights (plus spare bulbs).

1. (C) Evening

2. Four flip-charts and markers.

1. The colloquium will begin with an introduction of the panelists by the moderator, followed by a sequence of brief presentations by the moderator and the panelists. Thereafter, the panelists will have the privilege of asking each other questions before the general audience is invited to join in.

2. The total time allowed for the colloquium is 100 minutes (17 : 00–18 : 40); of which, each panelist will be entitled to 10 minutes of presentation, if he wishes to make one. However, if a panelist prefers to make no formal presentation, he/she will be given an equivalent amount of time for questions to the other panelists immediately following the formal presentations.

3. The presentations are not supposed to be lengthy ego trips (though slides and/or an overhead projector may be used, if necessary); rather, they should be a means to make an important point for discussion. Mutual challenges in a congenial atmosphere are encouraged. At the end of the Colloquium, the moderator will summarize the results, i.e., agreements, disagreements, and open or new questions.

Satellite symposia can save travel funds for both the main and satellite meetings. On the other hand, they may create problems for the organizer of the main meeting. To avoid this, satellite symposia lasting longer than one day should only be permitted under the following conditions:

1. They are held after the main meeting.

2. They do not compete for funds with the main meeting.

3. Their presentations are coordinated with those of the main meeting.

4. Their budgets are kept separate.

5. Travel support for participants of both meetings is coordinated.

The first condition is based on the experience that: (a) most people feel tired after several days of scientific discussions; and (b) a specialized meeting still attracts a good audience when the general interest is waning. If a general meeting follows a specialized symposium, the chances are that tired participants will either leave early, or spend more time in the hallways than in lecture rooms. And you, the organizer, will cringe at these ‘lobby lizards’ when the audience in some sessions drops to an embarrassing low.

On the other hand, a conference dealing with a topic directly relating to one's research has an enlivening effect, provided there is a chance for discussion, and not just another barrage of talks. Thus, a well-conceived satellite symposium should not suffer from a preceding main event. A good satellite symposium will provide opportunities for personal interaction, such as Workshops, Round Table Discussions with participation of the audience, and Poster Sessions.

The second condition is self-evident, but all too often ignored. An extreme case should make the point.

Dear Colleagues,

Enclosed with this note you will find the preliminary list of prospective participants in your workshop.

Undoubtedly further changes and additions will be requested; in particular, I foresee that some of you may wish to add participants to the list for your Workshop. You are welcome to do so, provided: (a) this person has agreed to participate; and (b) the person has registered, or will pay the fee for delayed registration upon arrival at the meeting. However, after February 15, it will be too late to add names to the printed program since the latter will then go press.

If questions concerning fees should arise, please make it clear to prospective late registrants that there will be no discount bargaining; in fairness to other participants, we must insist on the full payment for delayed registration.

I would like to emphasize that it is not necessary (and for time's sake not even desirable) that the participants introduce themselves with more than a few remarks on their research interests. After all, they should have submitted their ‘statement of research interest’ to you, and everybody should have had time to read the ‘statements’ of the other participants.

When you contact the participants of your Workshop, please include the sample of a ‘statement’ in your mailing.

Mini-Machiavellian management

Making and breaking of committees

According to an old adage, the camel is a horse designed by a committee. It may be difficult to express better the feelings of many people who have had to deal with committees.

Before you consider working with committees recall that, in general, they serve one of four functions: (1) to come up with something useful; (2) never to produce anything of consequence; (3) to fulfill a requirement without making waves; (4) to hide foregone conclusions behind a collection of yes-men.

The first type of committee is often set up, and may even deliver something meaningful. It requires qualified and cooperative members, and it functions best when chaired by an enlightened dictator.

The second type is useful when a problem requires benign neglect. The more members it has, the less likely it is to come up with something serious. Committees of the third type often exist in the form of editorial boards for the conference, or they advise on tantalizing matters such as ceremonies and protocol.

The last type of committee may better be termed ‘pseudocommittees.’ Usually, they are ad hoc collections of friends, or people who depend on the grace of the chair.

Someone experienced in dealing with committees will probably subscribe to the following rules:

1. Never set up a committee unless and before it is necessary.

2. Select committee members very carefully choosing persons who genuinely will participate and are qualified to do so.

3. If a committee is meant to function, keep it as small as possible, but as large as necessary.

4. If a committee does not function, dissolve it.

General considerations

In the selection of a meeting place, the odds for a mishap are probably greater than in Russian roulette, and they grow with the naiveté and/or laziness of the organizers). To avoid major mistakes, it pays to make thorough inquiries about potential meeting sites. The more information you can get, the better. Ask both organizers and participants of recent meetings. Why also ask participants? Because organizers often remain unaware of serious flaws; and, on the other hand, they may be reluctant to admit major mistakes. Of course, the best recommendation for a meeting place is when it is used year after year by the same scientific societies.

Never trust a hotel or meeting facility without a written contract. If they refuse to sign one that is to your satisfaction, thank them for the warning and go elsewhere. Scientists typically totally underestimate the tricks of the convention trade. The example of a contract in Appendix I gives you some idea of what a skillful negotiator can obtain for a major meeting.

Whenever possible, prepare a list of questions and contact by phone the organizer of a previous conference at your envisioned meeting site. Perhaps, you can persuade him to send you copies of his contract(s). If his meeting included exhibitions, also ask about contracts with the decorator and exhibition service (see Section 3.4). Ask the managements of the hotel and meeting site for copies of contracts with previous organizations. Their reactions may be revealing.

Why is a written, legally binding contract so important? The following experience will answer that question.

When I organized a major international meeting, I made oral arrangements with the manager of the congress hotel.

During the first few hours after each impact, numerous phenomena were observed with telescopes on Earth, in orbit, and in space. The primary events in that time were: impacts themselves, rise and fall of large plumes of ejected material, and atmospheric waves; also of interest were the characteristic morphologies of fresh sites. Based on timing from Galileo instruments and ground-based observations, the Hubble Space Telescope (HST) recorded actual impact phenomena for fragments G and W, with the A and E impacts occurring just prior to the HST observation window. For these four events, plumes were directly imaged; plume development and collapse correlated with strong infrared emission near the jovian limb, supporting the interpretation that the IR brightness was created by the fall-back of plume material from high altitude (see chapter by Nicholson). For medium-to-large fresh impact sites imaged by HST within a few hours of impact, expanding rings were detected, caused by horizontal propagation of atmospheric waves (see chapters by Ingersoll and Zahnle). Initial site morphology at visible wavelengths was similar for all medium-to-large impacts: a dark streak surrounded by dark material, dominated by a large crescent-shaped ejecta to the southeast. Smaller impact sites typically only showed a dark patch (no ejecta) which dissipated quickly. This chapter summarizes the most recent measurements and interpretations of plumes and fresh impact sites as observed by HST.

The dark clouds that were easily seen in small telescopes after the comet impacts were caused by small particles which were deposited in Jupiter's stratosphere. Observations from the Hubble Space Telescope and from ground-based instruments at visible and infrared wavelengths indicate that the mean radius of the particles is in the range 0.1 to 0.3 μm, and the total volume of particles is approximately the same as that for a 1-km diameter sphere. In the dark core regions of freshly-formed impacts, the particles are distributed over a large vertical extent, between about 1 mb and 200 mb or deeper. The diffuse outlying haze is confined to the high-altitude end of the range. Such a distribution probably reflects different methods of emplacement of the debris as a function of distance from the impact. The color of the particles, and their volatility as required to make waves visible, suggest an organic material as the main constituent. These relatively volatile materials are thought to have condensed onto more refractory grains after the plume material cooled, some 30 minutes or more after impact. The most refractory materials expected to condense from an evolving fireball are Al2O3, magnesium and iron silicates, and soot, depending on the C/O ratio. A silicate spectral feature was observed, confirming that cometary material was incorporated into the grains, although silicate grains make up only 10–20% of the particle volume.

Galileo observations in the UV, visible, and infrared uniquely characterize the luminous phenomena associated primarily with the early stages of the impacts of SL9 fragments—the bolide and fireball phases—because of the spacecraft's direct view of the impact sites. The single luminous events, typically 1 min in duration at near-IR wavelengths, are interpreted as initial bolide flashes in the stratosphere followed immediately by development of a fireball above the ammonia clouds, which subsequently rises, expands, and cools from ∼ 8000 K to ∼ 1000 K over the first minute. The brightnesses of the bolide phases were remarkably similar for disparate events, including L and N, which were among the biggest and smallest of the impacts as classified by Earth-based phenomena. Subsequent fireball brightnesses differ much more, suggesting that the similar-sized fragments were near the threshold for creating fireballs and large dark features on Jupiter's face. Both bolides and fireballs were much dimmer than had been predicted before the impacts, implying that impactor masses were small (∼0.5 km diameter). Galileo data clarify the physical interpretation of the “first precursor,” as observed from Earth: it probably represents a massive meteor storm accompanying the main fragment, peaking ∼10s before the fragment penetrates to the tropopause; hints of behind-the-limb luminous phenomena, recorded from Earth immediately following the peak of the first precursor, may be due to reflection of the late bolide/early fireball stages from comet debris very high in Jupiter's atmosphere.

Measurements of thermal emission in spectral regions, ranging from the near-infrared to mm wavelengths provide information on the atmospheric thermal structure over impact sites from μbar levels in the upper stratosphere down to the upper troposphere. Systematic time series of observations relevant to this entire height range over individual spots do not exist. However, by piecing together information at different times from various spots, it is possible to obtain a provisional, semi-quantitative picture of the behavior of the thermal structure over a typical impact site. Immediately after fall-back of the ejecta plume, the upper stratosphere is heated to ∼ 600–1300 K above ambient temperature. The amplitude of the temperature perturbation diminishes with increasing depth in the atmosphere, but even in the upper troposphere a temperature increase of a few kelvins is observed. Initially, the upper stratosphere cools very rapidly with time scales of tens of minutes, presumably the result of strong radiative cooling associated with the high temperatures. After the initial cooling, all levels continue to cool at slower rates with time scales of a few days; however, this is still very rapid compared to radiative cooling of the ambient atmosphere. Enhancements in infrared opacity necessary to produce the cooling radiatively do not appear to be viable, suggesting that dynamical effects may play a dominant role. Possible mechanisms include horizontal mixing with the ambient atmosphere and adiabatic cooling produced by upward motion associated with an anticyclonic vortex.

Two months after the discovery of comet Shoemaker-Levy 9 came the astonishing announcement that the comet would impact Jupiter in July 1994. Computing the orbital motion of this remarkable comet presented several unusual challenges. We review the pre-impact orbit computations and impact predictions for SL9, from the preliminary orbit solutions shortly after discovery to the final set of predictions before the impacts. The final set of predicted impact times were systematically early by an average of 7 minutes, probably due to systematic errors in the reference star catalogs used in the reduction of the fragments' astrometric positions. The actual impact times were inferred from the times of observed phenomena for 16 of the impacts. Orbit solutions for the fragments were refined by using the actual impact times as additional data, and by estimating and removing measurement biases from the astrometric observations. The final orbit solutions for 21 fragments are tabulated, along with final estimates of the impact times and locations. The pre-breakup orbital history of the comet was investigated statistically, via a Monte Carlo analysis. The progenitor nucleus of SL9 was most likely captured by Jupiter around 1929 ± 9 years. Prior to capture, the comet was in a low-eccentricity, low-inclination heliocentric orbit entirely inside Jupiter's orbit, or, less likely, entirely outside. The ensemble of possible pre-capture orbits is consistent with a group of Jupiter family comets known as the quasi-Hildas.

The breakup of Comet Shoemaker-Levy 9 is discussed both in the context of splitting as a cometary phenomenon, comparing this object with other split comets, and as an event with its own idiosyncrasies. The physical appearance of the comet is described, features diagnostic of the nature of tidal splitting are identified, and the implications for modelling the event are spelled out. Among the emphasized issues is the problem of secondary fragmentation, which documents the comet's continuing disintegration during 1992–94 and implies that in July 1992 the parent object split tidally near Jupiter into 10–12, not 21, major fragments. Also addressed are the controversies involving models of a strengthless agglomerate versus a discrete cohesive mass and estimates for the sizes of the progenitor and its fragments.

Introduction

Splitting is a relatively common phenomenon among comets, even though its detection is observationally difficult because companions are almost invariably very diffuse objects with considerable short-term brightness variations. Comet Shoemaker-Levy 9's behavior was generally less erratic than that of an average split comet, which may have in part been due to a major role of large-sized dust. The breakup products that contributed most significantly to the comet's total brightness are referred to below as components, or, because of their diffuse appearance, as condensations, both common terms of cometary phenomenology. The terms nuclei and fragments are instead reserved for genuine solid bodies of substantial dimensions (≳ 1 km across) that were “hidden” in the condensations.

A new analytical model that is calibrated against numerical simulations performed with the CTH shock physics code provides a useful description of the entry of Periodic Comet Shoemaker-Levy 9 into the Jovian atmosphere. Mass loss due to radiative heating of fragments larger than 100 m in diameter is insignificant because of energy conservation during the ablative process. Nevertheless, radiative ablation is a major contributor to atmospheric energy deposition at high altitude and plays an important role in early-time fireball evolution. The analytical model provides the initial conditions from which fireball and plume evolution can be calculated using CTH. The results from these simulations suggest that if the tops of the plumes originated from a specific level of the Jovian atmosphere then maximum plume heights are independent of fragment size provided the fragments penetrated at least 30 km below this level. If the tops of the plumes originated from the visible cloud tops, then fragment masses greater than 4 × 1012 g, corresponding to 200 m diameter fully dense water ice, are required to explain the observations. If the plumes originated from the NH4SH layer then masses greater than 3 × 1013 g (400 m water ice) are required. The lateral extent and mass of the observable plume are functions of fragment size and contribute to the lateral extent and albedo of the debris patterns after re-impact with the atmosphere.

The SL9 impacts are known by their plumes. Several of these were imaged by HST towering 3000 km above Jupiter's limb. The heat released when they fell produced the famous infrared main events. The reentry shocks must have been significantly hotter than the observed color temperature would imply, which indicates that the shocks were radiatively cooled, and that most of the energy released on reentry was radiated. This allows us to use the infrared luminosities of the main event to estimate the energy of the impacts; we find that the R impact released some 0.3 − 1 × 1027 ergs. Shock chemistry generates a suite of molecules not usually seen on Jupiter. The chemistry reflects a wide range of different shock temperatures, pressures, and gas compositions. The primary product, apart from H2, is CO, the yield of which depends only weakly on the comet's composition, and so can be used to weigh the comet. Abundant water and S2 are consistent with a somewhat oxidized gas (presumably the comet itself), but the absence of SO2 and CO2 shows that conditions were neither too oxidizing nor the shocks too hot. Meanwhile, production of CS, CS2, and HCN appears to require a source in dry jovian air; i.e., the airbursts occurred above the jovian water table. Tidal disruption calculations and models of the infrared light curves agree on an average fragment diameter of about half a kilometer.

Images of Jupiter taken by the Hubble Space Telescope (HST) reveal two concentric circular rings surrounding five of the impact sites from comet Shoemaker-Levy 9 (SL9). The rings are visible 1.0 to 2.5 hours after the impacts. The outer ring expands at a constant rate of 450 ms−1. The inner ring expands at about half that speed. The rings appear to be waves. Other features (diffuse rings and crescent) further out appear to be debris thrown out by the impact. Sound waves (p-modes), internal gravity waves (g-modes), surface gravity waves (f-modes), and rotational waves (r-modes) all are excited by the impacts. Most of these waves do not match the slow speed, relatively large amplitude, and narrow width of the observed rings. Ingersoll and Kanamori have argued that internal gravity waves trapped in a stable layer within the putative water cloud are the only waves that can match the observations. If they are correct, and if moist convection in the water cloud is producing the stable layer, then the O/H ratio on Jupiter is roughly ten times that on the Sun.

Introduction

Much of what we know about the interior of the Earth has come from the study of seismic waves—a branch of seismology. Recently, much has been learned about the interior of the Sun from helioseismology. Now, the SL9 impacts give us an opportunity to do jovian seismology. The waves probe Jupiter's atmosphere to depths that cannot be reached by remote-sensing instruments.