Science: Greeting Halley’s Comet

For more than three decades, as the frozen mass hurtled along its lonely path, the distant star had grown bigger and brighter in the blackness of space. Now the icy wayfarer was picking up speed, and the star had become a shining yellow sphere, its intense light illuminating the planets circling it. Basking in the rays of the star, the approaching comet warmed, giving off vapors that formed a growing cloud around it. And in the brightening light, the cloud began to glow.

For inhabitants of earth, the third closest planet to the star, the long- awaited spectacle had begun. After a 75-year sojourn through the solar system, Halley’s (rhymes with valley’s) comet had again swung into view, but just barely. At Kitt Peak National Observatory near Tucson one night last month, several large telescopes tracked the approaching comet, projecting images that flickered across television monitors. But like countless amateur stargazers around the world, the astronomers wanted to see the cosmic celebrity with their own eyes. Huddled in the chill mountain air outside an observatory dome, necks craned, binoculars raised, they and a group of visitors searched a patch of sky.

“I’ve found it!” somebody cried. “Where? Where?” a chorus responded. One of the astronomers gave directions, as though to an out-of-the-way restaurant: Begin with the Pleiades, a glittering cluster of stars known as the Seven Sisters, then look south to find two middling bright stars, then move half a binocular field to the northeast.

And there it was. The sight, however, was decidedly unspectacular. Because it was still too far from the sun to sport a visible tail, and 58 million miles away from earth, the comet looked like little more than a smudged and dusty fingerprint. Or, as Hyron Spinrad, a cosmologist from the University of California, Berkeley, declared, “It’s a wimp.” Still, everyone was delighted. For the skywatchers, the appearance of Halley’s was a once-in-a- lifetime event, and they viewed it as a sort of psychological and even spiritual landmark. Said Astronomer Susan Wyckoff of Arizona State University in Tempe: “Just to see it at all is a thrill.”

But for astronomers and other scientists, the thrill goes far beyond a squint through an eyepiece on a shivery night. Although experts warn that Halley’s latest go-round — or apparition, as they call it — could be the dimmest of the 30 visits in recorded history, from a scientific standpoint it will be nothing short of the Fourth of July. Next March, as Halley’s speeds toward its closest approach to earth, it will be greeted by five diminutive, instrument-crammed space probes, two launched by Japan, two by the Soviet Union and one by the eleven nations of the European Space Agency (ESA). The close encounters were set for March because that is when the comet passes through earth’s orbital plane, the same level in which the spacecraft travel. Over several whirligig days, the flotilla will scrutinize the comet in exhaustive detail, from the fuzzy gaseous cloud that surrounds its icy nucleus to the two tails that by then will be streaming for millions of miles behind it.

Like dancers in an intricately choreographed ballet, each craft will perform a variety of tasks, complementing and aiding one another every thrust of the way. Japan’s two probes, Sakigake (Pioneer) and Suisei (Comet), between them will study the solar wind and examine the hydrogen cloud surrounding the comet. The Soviet Union’s Vega 1 and Vega 2 will analyze the abundant dust motes and charged gases that envelop the comet’s nucleus. Most remarkable of all, data and pictures from the Vega twins will enable European scientists to chart Halley’s course precisely enough to allow their probe, Giotto, to come within about 300 miles of the nucleus, snapping thousands of photographs as it swoops by. Says Kunio Hirao, a former top official at Japan’s Institute of Space and Astronautical Science (ISAS), “This kind of space-based collaboration by scientists all over the world could never have been accomplished before.”

Although for budgetary reasons it opted in 1981 against launching a Halley’s probe of its own, NASA nonetheless remains smack in the middle of the action. The agency plans to dedicate part of two shuttle missions, including the flight that will boost aloft Teacher Sharon Christa McAuliffe, to comet- related experiments. The Solar Max satellite, brought back to life l8 months ago by a shuttle repair crew and now performing its normal duty of monitoring the sun, will examine Halley’s off and on for about 60 days. Pioneer 12, in orbit around Venus, will watch Halley’s when it ducks behind the sun. The U.S. is also a major backer of the International Halley Watch (IHW), a vast effort to coordinate the megabytes of comet information that will be generated both by the probes and at ground-based observatories around the world. According to the latest figures, some 900 professional astronomers from 47 countries will participate in the international venture. Says Ray Newburn, director of IHW for the Western Hemisphere: “We’re going to learn more about comets in the next few months than we have in the whole history of cometary science.”

There are good reasons for this intensive scrutiny. To astronomers, a comet is a sort of flying museum stocked with precious artifacts from the very earliest moments of the solar system. They hope that by peering into Halley’s cold heart and sniffing out the dust and gases that stream from its surface, they can discern the conditions that existed at the birth of the sun and the nine planets some 4.5 billion years ago. That in turn could reveal how common an occurrence the formation of planets around other stars may be, hence how likely it is that extraterrestrial life exists. “Comets are like a cosmic refrigerator,” says Paul Feldman, an astronomer at Johns Hopkins University in Baltimore. “They’ve internally preserved the whole history of the solar system.”

Still, the mounting mania greeting Halley’s return has less to do with science than with the comet’s reputation as a fiery harbinger of doom and its familiar role in presaging such events as the fall of Jerusalem in the 1st century or the Norman Conquest (see box). Indeed, for the public as well as scientists, 1986 may turn out to be the Year of the Comet. “The arrival of Halley’s comet is not just an astronomical event,” insists Joseph Laufer, ^ editor and publisher of a three-year-old Halley’s comet newsletter. “It’s a cultural event that links generations.”

Its notoriety notwithstanding, Halley’s is only one of a thousand or so comets that have been observed since the first reliable account of these enigmatic travelers, recorded by Chinese astrologers in 613 B.C. The Chinese were also the first to chronicle the comet now known as Halley’s — in 240 B.C. In the Western world, Aristotle tried to explain the nature of comets. He had divided the universe into two realms: the imperfect and ever changing world between the earth and the moon; and the flawless, spherical heavens beyond. Since comets do not look round and perfect, the Greek philosopher reasoned that they must originate somewhere between earth and moon. Going further, says Donald Yeomans, a comet expert at the Jet Propulsion Laboratory (J.P.L.) in Pasadena, Calif., Aristotle concluded that comets were “exhalations of the sins of man, ignited as they rose into the fiery sphere.”

Aristotle’s hierarchy had already begun to crumble by 1577, when the great Danish astronomer Tycho Brahe, by comparing observations of a passing comet made at the same time from several locations, correctly deduced that it was traveling in a celestial region beyond the moon. His conclusion not only advanced cometary science but effectively laid to rest Aristotle’s division between imperfect and perfect worlds. In 1680 Gottfried Kirch, a German calendar publisher, became one of the first observers to discover a comet with the aid of a telescope. Later that year a 24-year-old English astronomer on a visit to Paris made his first attempt to plot the path of a comet and failed miserably. Two years later at his home outside London, peering through a telescope he followed the progress of another comet, the one that would come to bear his name. The tall, ambitious young man was Edmond Halley.

In addition to his pre-eminence as a cometary pioneer, Halley was a brilliant mathematician, inventor and engineer. Some historians believe that he had still another calling — as a spy who kept track of the movements of the French navy while he charted the tides and coast of the English Channel for King William III. Halley kept extraordinary company as well. Among his most important colleagues was Sir Isaac Newton. To encourage the great physicist, Halley financed the publication of the revolutionary Mathematical Principles of Natural Philosophy, which presented Newton’s laws of motion and theory of universal gravitation, as well as the formula for calculating the force of gravity.

Applying Newton’s ideas, Halley in l695 determined that the orbits of 24 previously documented comets were cigar-shaped ellipses, in contrast to the more circular paths of the planets. More important still, he realized that certain apparitions spaced 75 to 76 years apart were probably reappearances of the same object. Making an enormous leap of confidence, he predicted in 1705 that the comet witnessed in 1531, 1607 and by himself in 1682 was periodic, and would reappear in 1758. “If this prediction is fulfilled,” he wrote, “there is no reason to doubt that other comets will return.” Halley died in 1742. Sixteen years later a German farmer named Johann Georg Palitzsch looked into the sky and became the first person known to have witnessed the comet’s return, thus confirming the Englishman’s bold prophecy.

The next two centuries of cometary science were relatively uneventful. In 1823 German Astronomer Johann Franz Encke, who calculated the orbit of a periodic comet that bears his name (it reappears every 3.3 years), insisted that the orbit of “his” comet could not be explained solely by gravity. He proposed that “ether,” an invisible theoretical substance that at the time was believed to pervade space, exerted drag on the nucleus, slowing it down. After observing flares streaming from Comet Halley’s surface in 1836, another German astronomer, Friedrich Wilhelm Bessel, conceived a more plausible concept, the fountain theory. Bessel proposed that a comet was a loose clump of particles. He suggested the flares were fountains of these motes erupting from its nucleus and that they acted as a brake. Bessel’s work was largely ignored at the time, but it turned out to be at least partially correct.

The next big breakthrough came in 1950, when Fred Whipple, a Harvard astronomer, proffered a detailed model for the anatomy of a comet. In a delightfully evocative phrase, Whipple declared that comets are “dirty snowballs,” dark conglomerates of mostly frozen water stippled with rocky fragments, dust particles and trace elements. As one of these snowballs swoops toward the sun, said Whipple, solar radiation begins to vaporize ice and frozen gases on the comet’s sunward surface by a process called sublimation. The gases, carrying dust with them, form a light-reflecting coma that makes the comet visible from earth.

Like the heated gases bursting from a jet engine, the departing cometary ! molecules exert a force on the icy nucleus, giving the comet its independent thrust. But because the ice does not vaporize uniformly and the nucleus rotates, the jet action propels the comet in many directions and can either accelerate or decelerate it. Apparently this accounts for the nongravitational motions that astronomers had previously observed. After 35 years of scrutiny, Whipple’s model of comet properties is still accepted today. “When I first realized about the jet action of comets,” says the 79-year-old astronomer, “Boy! That was a thrill.”

If comets are simply hurtling hunks of ice, where do they come from, and how do they get here? The same year that Whipple spun his theory of cosmic snowballs, Dutch Astronomer Jan Oort conceived of a kind of enormous warehouse for comets, which would come to be known as the Oort Cloud. Basing his calculations on the shape of cometary orbits and the number of new comets observed each year, Oort postulated that the cloud surrounds the solar system in a vast region 30,000 to 100,000 astronomical units from the sun (one AU is about 93 million miles, the distance between earth and sun).

The Oort Cloud, explains Berkeley’s Spinrad, would consist of at least a trillion “dull blocks of ice,” ranging from a few inches to a few miles in diameter. Out in that velvet blackness of space, where temperatures approach absolute zero, the snowballs remain unchanged, well beyond the effects of solar radiation, meteorite impacts, volcanic activity, atmosphere and other phenomena that have gradually changed the inner members of the solar system. Every once in a while, however, a passing star gives the cloud a gravitational jiggle, releasing hundreds of these fragments. Most of them are sent outward into interstellar space, but some are hurled toward the sun as comets. Although the Oort Cloud has yet to be seen, most astronomers agree it exists and is the flotsam left over when a nebula, a massive cloud of dust and gas, collapsed and formed the solar system.

Many other aspects of cometary theory have since been refined or expanded. By studying the spectra of light emitted from molecules broken down in the gaseous coma, scientists have estimated that a comet’s nucleus consists of two-thirds water, one-fifth dust (particles averaging one-thousandth the width of a pinhead) and the rest a mixture of methane, ammonia, carbon dioxide and trace elements.

When a comet is still as far away as 5 AU from the sun, about the distance of Jupiter, its most volatile material begins forming a coma that reflects light. By the time the most powerful telescopes first catch a glimpse of a comet, the coma already obscures the nucleus beneath. For every revolution a typical comet makes around the sun, its diameter is estimated to shrink about 6 ft. Hence the original size of the comet, the length of its orbit and how close it gets to the sun will determine its life-span. Astronomers estimate that Halley’s, which has a relatively short period, will probably last another 225,000 years, a mere wink of astronomical time.

Scientists long ago recognized that every comet has not one but two tails, not always visually distinct, both extending millions of miles by the time the comet has moved close to the sun. They now know that the yellowish, often curved tail is composed of dust particles released during sublimation and swept away from the sun by the pressure of solar radiation. Sunlight reflecting off the tail produces the fiery effect. The second, bluish appendage is called the plasma or ion tail. It is formed when gases from the comet’s nucleus become charged by solar radiation and then react with the solar wind, which is a constant stream of charged particles that emanate from the sun and carry its magnetic field. While the plasma tail does not reflect sunlight, it is visible because of the light emitted by some of its gases.

For all their knowledge and years of observations, however, astronomers have more questions than answers about Halley’s or any other comet. “Think about it,” says John Brandt, chief of astronomy and solar physics at NASA’s Goddard Space Flight Center in Greenbelt, Md. “We don’t even know what shape the nucleus is, or its mass or even its size. We don’t have a single photograph of that central lump.” Nor do scientists know such critical details as the exact ratio of elements within the nucleus or at what temperature the ice condensed. Such information could help determine which, if any, of the current theories about the beginnings of our solar system is most plausible. As it turns out, Halley’s is an ideal snowball to explore. Reason: it is the brightest known comet with a predictable orbit, which takes it on an elliptical trail from more than 3 billion miles from the sun, roughly halfway between Neptune’s and Pluto’s orbital paths, to within 60 million miles of the solar surface. Susan Wyckoff’s husband, Arizona State’s Peter Wehinger, a quasar researcher who is now interested in Halley’s comet, says, “We’ve been able to plan for it for years.”

The scheme to mount a rendezvous with Halley’s first came up in the mid-’70s, when NASA and ESA began discussing a double-barreled mission that would involve encounters with two comets, including Halley’s. In January 1980, however, the U.S. dropped out of the project, largely because the billion- dollar price tag was just too high. American scientists were outraged, and the Europeans were dismayed. As it was, European space officials who supported the Halley’s encounter had worked hard to sway those who would have preferred spending ESA funds on a lunar landing. “We’d finally convinced everyone to do the comet mission,” says Roger Bonnet, now director of ESA’s scientific programs. “So when NASA informed us it was dropping out, that caused another crisis.”

The crisis was short-lived: within six months the ESA nations decided to go ahead with the rendezvous anyway. Freed of their ties to the U.S., they gave their spacecraft a very European name: Giotto, after the great Italian painter who had depicted Halley’s comet in his early 14th century fresco Adoration of the Magi. Lingering doubts about the encounter quickly vanished. Says British Engineer David Dale, project manager in charge of the construction and operation of Giotto: “It was exciting, it was sexy . . . and it was something that only happens once in a lifetime.”

Other nations apparently concurred. The Soviet Union, which had already been planning a two-ship mission to study the atmosphere and surface of its favorite space target, the planet Venus, agreed to add a Halley’s encounter to the twin spacecrafts’ agenda. That dual purpose was reflected in the chosen name Vega, a contraction of the Russian names for Venus (Venera) and Halley (Gallei). In 1984 Japan’s ISAS put the finishing touches on two Halley’s probes, that country’s first foray into interplanetary exploration.

Japan’s contribution will be the more self-contained segment of the encounter. The two probes, one launched in January, the other in August, are similar in design. Each drum-shaped craft weighs about 308 lbs., measures 4.6 ft. by 2.3 ft. and sports three antennas. Their functions, however, are quite different. Sakigake, which will never venture closer than 4.3 million miles from the comet’s nucleus, began its task last February of measuring the speed, density and temperature of the solar wind that blows against the comet. That information may reveal whether turbulence in the solar wind is responsible for curious irregularities seen in Halley’s tail in 1910 and in other comet tails. “Solar winds have a strong effect on the beautiful shape of the comet, the brilliance of the coma and the long tail,” says Hirao. “Now we’ll be able to recognize the wind that will disturb the comet four or five hours before it actually makes contact.”

Sister probe Suisei, on the other hand, will dart within 90,000 miles of the comet’s heart on March 8. Equipped with an ultraviolet camera and energetic- particle analyzers, it will investigate Halley’s corona, a cloud of neutral hydrogen atoms that extends 6 million miles outward from the comet. Ultraviolet photographs of the corona taken at varying distances will help scientists estimate the evaporation rate of the icy nucleus. “We’re interested in how much mass the comet loses during one tour of the sun,” says Tomizo Ito, head of the Halley’s project at ISAS. “That way we might be able to say how long the comet will survive.” The particle analyzers will examine the composition of the ions in the coma.

Like the Japanese spacecraft, the Soviet probes, which blasted off six days apart last December, appear to have been built from the same blueprint. They are roughly 16.5 ft. high and 30 ft. across from solar panel to solar panel. Both probes began life with landing modules topped by a payload-toting helium balloon. After traversing 313 million miles, Vega 1 reached Venus on June 11. Its module-balloon contraption detached and then separated 33 miles above the planet’s surface. The module made a soft landing on the ground, while the payload attached to the balloon tested weather, wind currents and the chemical makeup for about 46 hours before being destroyed in the atmosphere. Four days later, Vega 2 released its module and balloon for a similar round of tests. The probes then set off for their much trickier rendezvous with Halley’s. According to current plans, Vega 1 and Vega 2 will encounter Halley’s on March 6 and 9, respectively. Vega 1 will fly through the coma about 6,000 miles from the nucleus; Vega 2’s path will be determined by the success of Vega 1. Their cameras will snap photographs of the coma in visible light, and infrared spectrometers will examine the molecules that sublime from the surface. An extraordinary device aboard both spacecraft will analyze the mass of dust particles, seeking clues to their density and chemistry. Designed by John Simpson, a physicist at the University of Chicago, the analyzer is the first American-made interplanetary instrument to fly on a Soviet spacecraft.

One of the most important contributions from the Vega program will be what is called the Pathfinder concept. Together the probes will attempt to reckon the position and orbit of Halley’s nucleus with a precision impossible from ground-based observations and then beam the data back to the Soviet Union, which will in turn relay the information to European mission control in Darmstadt, West Germany, in time for Giotto’s rendezvous on March 13. Precision is of the essence: zeroing in on a nucleus that scientists estimate measures only two to six miles in diameter and is traveling some 154,000 m.p.h. is no mean feat. Without help from Vega 1 and 2, Giotto could be as much as 6,000 miles off the route projected to take it within 300 miles of the snowball. That much of an error could send it either too far from the nucleus to get the desired results or crash it into the comet. Says ESA’s Bonnet: “This is going to be the most difficult observation ever made in interplanetary space.”

Indeed, Giotto’s mission is by far the most grueling of the five. Looking rather like an oil drum with an upended beach umbrella stuck on top, the 5-ft. by 6-ft. probe was launched from Kourou, French Guiana, last July; as of last week it was 21 million miles from earth and nearly three times as far from Halley’s. The little ship and everything on it are built for survival, and with good reason. The dust particles around the nucleus are expected to strike Giotto with such great velocity that a speck weighing a tenth of a gram would penetrate an aluminum plate about 3 in. thick. To prevent damage, the side of the craft facing the comet is covered with a double shield, one made of aluminum and the other of Kevlar, the material used in bulletproof vests. Even then, Giotto is not expected to survive the encounter unharmed. A collision with a large dust particle or small meteoroid could ruin the entire operation. “The biggest danger we face,” says Bonnet, “is that the craft’s antenna will be knocked out of alignment and we will lose control over it.”

Should the probe weather its many assaults, the rewards will be splendid. During its four-hour encounter, Giotto will explore the material streaming from the nearby nucleus with a total of ten experiments. As the craft revolves on its axis, a solid-state optical camera extending from the bottom rim like a bent stovepipe will snap a photograph once every four seconds. The pictures will be instantly transmitted to earth and shown live on television. Mass spectrometers will analyze the composition of the dust from the nucleus, and other instruments will examine the properties of the ions in detail and measure the magnetic field girdling the comet’s head. To prevent contamination of the surrounding space by the exhaust from Giotto’s thrusters, controllers will turn off the engines at least 24 hours ahead of time. Says David Dale: “We don’t want to come away from the encounter convinced that the comet is made of hydrazine (rocket fuel).”

As crowded as it will be in Halley’s neighborhood, scientists regret that one additional probe did not make the trip — a U.S. craft proposed by Goddard Space Flight Center in March 1981 that would have sampled the comet’s dust and gases and returned to earth orbit, where it could have been picked up by the shuttle in 1990. Unfortunately, because of squabbling over just how elaborate the craft should be and what equipment it should carry, as well as a budgetary squeeze, the U.S. probe never got off the drawing boards. For all their disappointment at not getting their own probe, however, American astronomers have been playing an excellent game of catch-up. Last September, after a year and a half of maneuvering, NASA engineers deftly redirected a satellite that had been in orbit since 1978 so that it would fly through the tail of Comet Giacobini-Zinner, making it the first man-made object to encounter a comet. The International Cometary Explorer, as it was rechristened for its encore performance, revealed important data about the nature of the tail and the bow shock, a shock wave that is set up when the supersonic solar wind is slowed to subsonic speed by the comet plowing through it. The success of ICE, says an admiring Bonnet, “enabled the U.S. to be first again, and that is what NASA really cares about.”

Two other old space hands, Solar Max and Pioneer 12, have been assigned cometary tasks. Solar Max’s coronagraph-polarimeter (an instrument for photographing the sun’s corona) will temporarily be twisted from its normal position to study Halley’s dust and gas tails near perihelion (point of closest approach to the sun) in order to gain some knowledge of how the solar wind functions. The satellite might even be lucky enough to catch a “disconnection event,” when the comet’s tail snaps off and then re-forms. This phenomenon occurs when a comet crosses a sharp break in the solar wind, where the magnetic field shifts. “Halley’s comet is really going to make or break a lot of theories,” says NASA Physicist Malcolm Niedner, an expert in comet tails. “Nothing is sacred, everything is up for testing.”

Later this month, before the five-ship armada reaches Halley’s, Pioneer 12, the Venus orbiter launched in 1978, will be relieved of its tasks, which include long-term observations of the solar wind’s effects on the cloud-veiled planet. It will be ordered to aim its ultraviolet spectrometer toward the comet before, during and after perihelion, when Halley’s is most active because of its proximity to the sun.

The space shuttle will also be an important player in the comet capers. On a flight in January, shuttle astronauts will oversee the release of SPARTAN, yet another acronym, which stands loosely for shuttle-pointed autonomous research tool for astronomy. A free-floating instrument package will be ejected from Challenger’s cargo bay and allowed to drift in space for 45 hours, during which time it will aim two ultraviolet spectrometers at Halley’s from a distance of more than 100 million miles.

Two months later, Columbia will bear a $55 million payload named Astro-1 that includes three ultraviolet telescopes and two wide-angle cameras. For much of the mission, the instruments will be studying such exotica as quasars, black holes and globular clusters, but for a while during the days that the five international probes encounter the comet, all of Columbia’s eyes will be on Halley’s. One of the Astro-1 telescopes will peer at very short wavelength light to see if it can detect such elements as helium, neon and argon, which would reveal something about what temperatures were like at the time the solar system formed. If neon were detected, for example, scientists would have to lower their estimates of the temperature at which comets coalesce. A second telescope will measure the polarization of light and spectral distribution, which will provide clues on the size and shape of the comet’s particles.

NASA scientists insist that given the briefness and the danger of the flybys, Astro-1 could actually end up gleaning more information about Halley’s than the probes do. “Our mission may not be as dramatic,” says Knox Long, a Johns Hopkins University scientist on the Astro project, “but we’re getting the most bang for the buck.”

The view from ground-based obser vatories is of great impor tance as well. It was with the mammoth 200-incher at Palomar Observatory in California that Astronomers David C. Jewitt and G. Edward Danielson first spied Halley’s, on Oct. 16, 1982, when it was more than 1 billion miles from earth. Ever since then, most of the world’s major telescopes have been trained on the comet at some point. At Lowell Observatory in Flagstaff, Ariz., Astronomers Lawrence Wasserman and Edward Bowell have calculated 40 points on the comet’s route at which it will pass directly in front of a relatively bright star. During one of these passages, which are expected to last about 15 minutes, they hope to learn how dust is distributed in the coma by analyzing the starlight shining through it. At Mauna Kea Observatory in Hawaii, nearly 14,000 ft. above sea level, Astronomer Dale Cruikshank is using infrared photometry and imagery to measure the heat radiation from Halley’s coma and the distribution of dust within it, as well as to look for certain isotopes of carbon and hydrogen. Says he: “I’m convinced there’s some organic material in the comet.”

Overseeing the worldwide operation is the International Halley Watch, perhaps the most complicated scientific project ever organized. NASA has allocated $10 million to the effort for a ten-year period that began in 1980, while the West German government is contributing about $80,000 through 1986. One major thrust of the effort is to provide scientific standards for every phase of the Halley’s observation. “It’s open season on the comet,” says Donald Yeomans. “We’ve got to be sure that all observers are using the same techniques and the same filters so that all the data can be compared.” The watch is broken down into eight disciplines, ranging from spectroscopy to the study of spatial motion. Scientists at both J.P.L. and IHW East headquarters in Bamberg, West Germany, spend a lot of time on the telephone as well; J.P.L. estimates that it receives 150 comet-related calls a week from observers around the world. “A good deal of our work is public relations,” says Astronomer Horst Drechsel, deputy leader of IHW East, “and we get school field trips coming through here every week.”

In March and April, when Halley’s will be at its brightest, many astronomers will flock below the equator, where viewing will be most favorable. By then the comet should have tails stretching tens of millions of miles, and at southern latitudes it will appear almost directly overhead. Two favored vantage points will be the southern counterpart of Kitt Peak, Cerro Tololo Inter-American Observatory in Chile, and Siding Spring Observatory in rural Australia. Says an idealistic Don Mathewson, director of Siding Spring: “Comet Halley symbolizes a time when nations will put aside their earthly concerns and differences to share in contemplating the wonder of the universe.”

More than a few experts will contemplate that wonder aboard luxury liners, lecturing about the comet to well-heeled tourists who have paid as much as $8,000 for a Halley-centered cruise. The Royal Viking Star, which will sail on March 26 from Auckland, New Zealand, to Sydney, Australia, with Carl Sagan and other astronomers on board, has been booked solid since the beginning of the year. Not all scientists have accepted cruise offers. Says Yeomans: “After paying for the cruise to see the comet, passengers are going to be disappointed with what they see. They’re going to look for an astronomer to throw overboard, and I don’t want it to be me.” Not to be deterred by professional warnings, tens of thousands of Halley’s fans are headed south for the view. Accommodations in Australia are in such demand that families are being asked to billet tourists. Many North Americans are expected to fly to Sao Paulo, Brazil, where the state government has planned a monthlong festival beginning March 13.

Because the comet is now higher in the sky for northerners than it will be in the spring, Halley’s hype is beginning to approach fever pitch. New York City Mayor Ed Koch has suggested that the city consider dimming its lights during prime viewing periods. Companies that were burned by the disappointing appearance of Comet Kohoutek in 1973 are now confident that Halley’s, as a known quantity, is worth promoting. Total sales of everything from Halley’s books, bags, T shirts, running shoes, jewelry, wine and bumper stickers to sophisticated telescopes and binoculars could go as high as $500 million by mid-1986. Says Owen Ryan, president and founder of General Comet Industries, a Manhattan-based licensing outfit: “It’s gone beyond comet mania. It’s insane.”

Many octogenarians — and those close to becoming one — are going to be treated to something money cannot buy: a second look. The “1910 Halley’s Comet Club,” organized by the Hansen Planetarium in Salt Lake City, boasts more than 300 members. Memories of the brilliant 1910 visitation, when Halley’s passed within 14 million miles of earth (in contrast to 39 million . this time), are strikingly vivid. Blanche Stover Bennett of Pasadena was six years old when she saw the comet above a churchyard in Willow Springs, Mo. “It moved slowly and majestically, like a gorgeous fish,” she says. “It seemed so close that you felt you could have reached out and touched it.” Edmund Paul Halley, a descendant of Edmond Halley’s second cousin, was a nine- year-old boy living in Kalamazoo, Mich., when his grandfather gave him the responsibility of watching over the comet. Recalls Halley: “He said my father wouldn’t be around when it came back again, so he might as well leave it in my care.” Now a resident of Stockton, Calif., Halley plans to pass that responsibility to three of his six great-grandchildren. After all, at ages five, seven and nine, they should be around in 2061, when Halley’s comet returns for its next celestial show.