The crash of fragment A was an extraordinary event all by itself. That was the first time that people had witnessed such a collision. Had A been the only impact, we would have rejoiced and studied its effects for years. But in the opera of impact week, A was just the overture. One of the smallest nuclei, A was hitting the planet at a place farther away from Jupiter's daylight side than any of the others, so few scientists—Gene Shoemaker was one—expected to see the plume of material thrown into the atmosphere by its strike.10
The opera Levy may have had in mind was Gian Carlo Menotti's Amahl and the Night Visitors, whose young hero tells his mother that there is a colossal star over their house, but he is not believed. One after another, the long line of flying icebergs struck Jupiter, each time causing a huge explosion and a gas plume.
What happened next as the astronomers and other scientists watched on monitors the successive impacts belied the widely held belief that science is basically dull and so are its practitioners. “For a moment the group of scientists just sat there, stunned,” Levy later reported. “There was a collective gasp. It took a few more seconds before the scientists began to realize what a treasure they had, that in this one picture, all the months of planning had paid off handsomely. ‘Oh,’ Heidi Hammel exclaimed. ‘My God!’”
Levy remarked, “The whole picture was clear now, and the room erupted with cheering and applause. ‘We realized that we had something truly spectacular on our hands,’ Hal Weaver continued. ‘Melissa McGrath ran upstairs to get the champagne that she had bought for the occasion (even though she is the first to admit that she hadn't really expected to see anything like this), and Heidi Hammel popped the cork.’”11
New York Times journalist William J. Broad reported, “The Chicken Little crowd, which once drew smiles by suggesting that Earth could be devastated by killer rocks from outer space is suddenly finding its warnings and agenda taken seriously now that Jupiter has taken a beating in recorded history's biggest show of cosmic violence.” The story's headline made the point explicitly and accurately: “When Worlds Collide: A Threat to the Earth Is a Joke No Longer.”12
As is true in most other (pardon) groundbreaking work, the hunt for large, potentially dangerous rocks that have profoundly affected Earth or that could threaten it, perhaps catastrophically, has attracted a variety of people with widely varying opinions.
George Darwin, whose father, Charles, wrote On the Origin of Species, one of the towering works of science, was understandably interested in origins, too; though he was interested in the Moon's origins, not homo sapiens’. In 1878 he came to the conclusion that the Moon was probably flung off Earth when the planet was mostly liquid and rotating; that is, the two bodies had simply come apart and gone their separate ways. The theory quickly gained popularity not only in the scientific community but also among the general public, where the ancient romantic myth about the Earth goddess giving birth to the Moon goddess was happily resurrected and cherished. Four years later, a geologist named Osmond Fisher embellished the theory when he announced that the Pacific Basin was the birth scar, or depression, that resulted when the Moon separated from her—her—mother.13 If true, it would undoubtedly have been the worst case of a postpartum depression in the history of this world.14 But no evidence to support that kind of event has ever turned up.
Then there was Thomas Jefferson Jackson See, a supremely fatuous, unscrupulous, arrogant, self-promoting, altogether implausible character whose otherwise credible research and discoveries were almost entirely eclipsed by his blatantly incorrect, but stubbornly held, belief. He was adamant that the Moon was really a full-fledged planet in its own right that came from a place very far away and happened to be passing Earth when it was pulled in by this planet's more powerful gravitational field and was thus forced into a permanent orbit.
See was born in Missouri in mid-February 1866, studied astronomy at the University of Berlin, and, appropriately, died on the Fourth of July, 1962.
He was one of science's most memorable and enigmatic characters: a professional astronomer with a colossally inflated ego who had the manner of a colorful vaudevillian like the ones performing seemingly wondrous feats on stages in music halls while he was doing about the same thing in observatories. See's contributions to astronomy, and to the study of binary stars in particular, were widely recognized and eventually won him mention in the Encyclopedia Britannica.15
But T. J. J. See was the polar opposite of the popular image of the quiet, self-effacing scientist who puts long, lonely hours of research and discovery above blatantly obvious self-promotion. (That is not to say reputable scientists do not promote themselves. They certainly do. But it is customarily done with apparent modesty and at least the veneer of discretion.) Not so with See. He reveled in the kind of personal and professional self-absorption, bombast, and arrogance that brought scorn and contempt from the staid and usually understated astronomical community. He landed his first job in George Ellery Hale's prestigious department at the University of Chicago, where he was judged not fit for promotion by the distinguished astronomer and was therefore effectively forced to leave. His next stop was the Lowell Observatory at Flagstaff, Arizona, another top-notch institution. But he treated the staff with undisguised contempt for being mere underlings—in effect, his professional servants—and they reacted the way others in their predicament very often do; they found quiet but effective ways to slow their work to the point at which it impeded the astronomy. His departure was therefore inevitable. See's next stop, in 1898, was the US Naval Observatory in Washington, DC, where his carelessness and by then renowned egocentricity again caused angst.
See published Researches on the Evolution of the Stellar Systems, Vol. II, The Capture Theory of Cosmical Evolution, a book that ran to more than seven hundred pages and was therefore physically, as well as intellectually, very weighty. In it, he argued that space is not and never was a vacuum. Rather, it was filled with a tangible “resisting medium” that slowed the approaching Moon—which, he pointed out, could not have happened in a vacuum—until, after a great deal of time had passed, it was moving slowly enough to be captured by Earth and pulled into a permanent orbit around the planet. Furthermore, he added, all the planets in the Solar System had been captured by the Sun in precisely the same way. The resisting medium, See explained, was as fundamental to celestial mechanics as Newton's law of gravity.16
That the theory was wrong was bad enough. But it was also tainted by a blatant meanness. He described his task, for example, as being necessary to “brush aside the erroneous doctrines heretofore current, as one would the accumulated dust and cobwebs of ages.”17 That gratuitously malicious jab almost undoubtedly left many of his fellow astronomers muttering angry retorts to themselves and their colleagues.
Three years later, in 1913, newspaper publisher and amateur astronomer William Larkin Webb published a saccharine biography of See that once again confounded the astronomical community. Brief Biography and Popular Account of the Unparalleled Discoveries of T. J. J. See, as it was called, mirrored his grossly inflated ego. As would be expected, it was swollen with adoring hyperbole. Given See's nature, it was understandable that a rumor quickly started circulating that the self-created superstar of the stars had in fact written it himself.
A reviewer for the Nation was so put off by the book's blatant infatuation with its subject—a tone that in other circumstances has been likened to drowning in warm honey—that he or she in effect held up a mirror: “The infant See, we are told, first saw the light on the 393d anniversary of Copernicus's birth…[and] showed himself ‘every inch a natural philosopher’ by speculating on the origins of the sun, moon and stars at the tender age of two, never so much as dreaming that he should grow into a little boy with ‘methodical methods,’ and one day become ‘the greatest astronomer in the world.’”18 Meanwhile, to his eternal discredit, See also called Albert Einstein a fraud and a plagiarist. Einstein would not lend credence to See by responding, choosing not to sling the
mud back and maintaining a dignified silence that added to his stature.19
Harold C. Urey, the brilliant, acid-tongued chemist who won the Nobel Prize in 1934 for discovering deuterium, also believed that the Moon was captured by Earth. It was therefore not inherently a satellite of this planet, he reasoned, but rather the fifth of the inner planets that included Mars or the tenth, if the group extended out to Pluto. The latter was eventually demoted to a mere “planetoid” or “dwarf planet” by the International Astronomical Union after astrophysicist Neil deGrasse Tyson, the irrepressibly enthusiastic and animated head of New York's Hayden Planetarium, called for its status to be lowered. He was promptly deluged with hate mail from irate grade-schoolers who identified the newly downgraded (and therefore insulted) member of the Solar System with Walt Disney's beloved pooch of the same name.
So there it was: Darwin the Younger's “fission” theory had it that Earth and its Moon were once a single entity that had come apart on its own in a cosmic split or divorce. See's and Urey's “capture” hypothesis argued that the Moon had once been going its own way but was snagged by Earth and pulled into a permanent embrace. And finally, there was a “coaccretion” theory that maintained both Earth and the Moon were simply created independently when everything else was.20 The theories were of course considered eminently plausible by their adherents, all of whom believed that theirs was undoubtedly the most likely to have occurred. Collectively, the three explanations seemed to cover all the possibilities.
But nowhere, at least in the astronomical big leagues, was there mention of the fact that the Moon could have been formed when a planet-sized wanderer smashed into Earth with such force that it knocked off a large piece of it, which, over millennia, gradually turned from a jagged chunk of soil, rock, and minerals into a sphere like the other moons and then began circling its “mother.” It wasn't until well into the twentieth century that the true level of violence in the universe began to be seen and understood. It was nothing short of phenomenal. As telescopes improved, whole galaxies could be seen to collide, and the Moon's craters, which had been caused far more by impacts than by volcanoes, offered stark proof that Earthlings (and who knew, maybe Martians, too) live in a universe where violence and destruction occur constantly and are so massive that they are literally unimaginable (“mind-boggling,” the overused cliché, is appropriate). The mystery of how the Moon came to be was finally solved when teams of geologists and geophysicists, working independently but with access to some of each other's research, discovered why the dinosaurs disappeared.
Science is wholly dependent on sharing discoveries, so, unlike Thomas Jefferson Jackson See, those who investigated the disappearance of the dinosaurs tended to be generous to each other and highly professional in describing their monumental collective accomplishment.
The first important clue about this planet's turbulent history, and therefore about the state of perpetual violence in which it exists, turned up in Mexico in 1952. Geologists working for Petróleos Mexicanos, the Mexican national petroleum cartel, were searching for oil off the Yucatan Peninsula when they found pieces of hard, dense, crystalline rock instead of the porous, relatively soft, sedimentary rock in which oil is found. Crystalline rock is called that because it contains crystals. And crystals—as in glass—are made when minerals are subjected to enormous pressure and heat. An analysis of the rock samples also showed that they contained a composition similar to andesite, a fine-grained rock that is found in volcanic rock.21 They did not turn up any oil, and the reason quickly became clear, or at least the geologists thought it did. Volcanic rock does not contain oil. It was therefore decided that a long-dormant volcano was under the water just off the Yucatan coast, beside the village of Chicxulub.
But Petróleos Mexicanos, ever thinking about the lucrative market for crude oil, would not abandon hope that it was there somewhere. It therefore sent two geophysicists, Antonio Camargo Zanoguera, who came from the area, and an American named Glen Penfield, to press the search in the late 1970s. They, too, could not find oil. What they did find, however, revolutionized humanity's understanding of its history and, to a considerable extent, its place in the Solar System and the universe beyond. Zanoguera and Penfield discovered the clear outline of an almost-perfect semicircle that measured 180 kilometers across. The perfect geometry intrigued them, so they took a closer look, collecting rock and sediment samples as they went. Since volcanoes do not contain oil, the cartel called off the search. But Zanoguera and Penfield continued to explore the area and soon found the outline of another partial arc on the Yucatan Peninsula itself; on land. The two semicircles came together almost perfectly to form a 180-kilometer-wide circle whose center was near Chicxulub. That circle could have been caused only by an enormous natural “event” of some kind, and there were only two possibilities: a volcanic eruption or an impact. But, except for the material that closely approximated andesite, there was no evidence that the circle had been caused by a volcano. That, in addition to the crystalline rocks, finally started them thinking about the possibility that the great circle had been caused by an asteroid or a comet, which they calculated would have had to have been roughly ten kilometers wide and moving at blistering speed. To use Shoemaker's analogy, it would have been like a bullet fired into a pumpkin.
Walter Alvarez, a geologist at the University of California at Berkeley, became intimately involved in proving that the devastation at Yucatan was the work of an impactor. He has described what he believes would have happened when a very large impactor that he called “Doom” suddenly appeared:
Doom was coming out of the sky, in the form of an enormous comet or asteroid—we are still not sure which it was. Probably ten kilometers across, traveling tens of kilometers a second, its energy of motion had the destructive capability of a hundred million hydrogen bombs. If an asteroid, it was an inert, crater-scarred rock, dark and sinister, invisible until the last moment before it struck. If a comet, it was a ball of dirty ice, spewing out gases boiled off by the heat of the Sun, and it announced impending doom with a shimmering head and a brilliant tail splashed across half the sky, illuminating the night, and finally visible even in the daytime as Armageddon approached.22
Alvarez is the son of the late Luis Alvarez, a Nobel laureate in physics. He, his father, and two colleagues who were chemists, Frank Asaro and Helen V. Michel, decided to investigate the impact theory in 1980, soon after Zanoguera and Penfield went public with it. Alvarez and his colleagues knew when they began that the element iridium is relatively scarce on the surface of the Earth because it is very dense and much of it, therefore, sank when the planet was forming. But there is a lot of iridium in asteroids and in some meteorites. They found that more of it is concentrated in the sediment at Yucatan than is scattered elsewhere on the planet. In addition, they, like their oil-prospecting predecessors, turned up “shocked quartz granules,” which is to say minute amounts of primitive glass. That, again, was clear evidence that the area had once been incredibly hot and under enormous pressure.
“It is very difficult to appreciate the impact that was about to occur, because such an extreme event is far beyond our range of experience—for which we can be most grateful!” Walter Alvarez has written.23
One can write down the measures of what happened—an object about 10 km in diameter slammed into the Earth at a velocity of perhaps 30 km/sec. But these measures only acquire meaning when we try to visualize them, or make analogies to help our understanding. How can we imagine a comet 10 km in diameter? Its cross section about matches the city of San Francisco. If it could be placed gently on the surface of the Earth it would stand higher than Mount Everest, which only reaches about 9 km above sea level. Its volume would be comparable to the volume of all the buildings in the entire United States. It was a big rock, or a big ice ball, but not of a scale beyond our comprehension.24
What turned it into a cataclysmic weapon was its velocity. The estimated impact velocity of 30 km/sec is 1,000 times faster than the speed of
a car on the highway and 150 times faster than a jet airliner.25
Walter, his father, Asaro, and Michel wrote a paper on what they discovered for the journal Science, which published their findings in its June 6, 1980, issue.26 That paper played a crucial role in shaping the United States’ planetary-defense space program that its authors could not possibly have foreseen.
When that monster struck, it sent so much debris into the atmosphere that the sky was darkened for months, blocking life-giving sunlight and therefore not only finishing off the dinosaurs but also many other species of animals and vegetation. It was, in effect, what would be called a “nuclear winter” during the so-called Cold War that occurred sixty-five million years later, when other dinosaurs, now grossly shrunken but still walking on two legs, reappeared on both sides of what they called an “iron curtain” and threatened to obliterate most of the world with nuclear weapons. The extinction of the great reptiles and more than half of the other species of the time is generally relegated to a time so ancient, so lost in the mist of history, that it is irrelevant. But that is wrong. The huge asteroids and comets are still out there, and the possibility of this planet suffering another catastrophic hit is not only real but also probable. In the words of Robert F. Arentz, a corporate executive who is highly knowledgeable on the subject, “It's not a matter of if; it's a matter of when.”27
Asteroid Threat : Defending Our Planet from Deadly Near-earth Objects (9781616149147) Page 4