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Extinction and Survival

World 'must tackle space threat' Dec 2008

Keep the Moon's Precious Water  Do not waste it!
The moon could provide a sanctuary to protect humankind's future from an asteriod or comet strike. NASA would use it non-recyclably and waste it in a century or two. This is the suicide of humanity's second-option sanctuary for the future!

Risks of Supernovae The nearest stars should be surveyed for the risks of nearby surernovae. If such risks are possible, an underground 'space-station' on Earth should be set up on the lines of biospheres 2 to preserve humanity and critical species in the efent of a nearby supernova.

Asteroids - are we doing Enough? Apr 2003

Asteroid threat is greater than ever Tracking dangerous asteroids is no longer enough, its time to make sure we can fend off any coming ourway NS 14 sep 02

Space rock's close approach Thursday, 20 June, 2002

Space rock 'on collision course' Wednesday, 24 July, 2002

US military wakes up to asteroid risk 2002

Will we be wiped out by a super-eruption? 2002

MASS EXTINCTION Lone Offender Killed the Dinosaurs Sci Am. 2000

Wipeout Did a comet cause Earth's biggest ever mass extinction? NS 3 Mar 2001

Asteroid and Comet Risks and Strategies NS 3 Mar 2001 42

Asteroid comes out of sun Feb 02

The end of the world NS 2002 How big must an asteroid be to destroy civilisation?

Asteroid misses Earth by 4 hours by Cahal Milmo NZ Herald Independent 9 Jan 2002

Doomed asteroids point to Earth-like planets fit for life

Too hot?- Just move the Earth NZ Herald June 2001

Destroyer of worlds They bring death and destruction-and a fortune in gold ns 26 jan 02

'Stupendous' comet pictures revealed 25 September, 2001, BBC

Asteroid's mystery 'blue ponds' 26 September, 2001, BBC

Is This the End?
Selected extracts from THE NEW YORKER article , January 27, 1997 Timothy Ferris

It is very unlikely that a major comet will crash into the earth - but not so unlikely that leading scientists around the world haven't begun to plot ways to make sure it doesn't happen.

Scattered enclaves of humans may survive a major commet impact but human civilization almost certainly will not.


On the final night, debris blown off the comet as it passed near the sun starts striking Earth. Fireballs light up the sky. A meteorite punches a hole in an apartment house in Morocco. Another sets fire to oak trees in Anatolia. The comet hits near Bermuda just before dawn Eastern time. The explosion vaporizes an enormous sphere of air, seawater, and sou, cutting a crater a hundred mues in diameter in the ocean floor. This makes a thunderdap that rolls through Philadelphia and New York a little over an hour later and will thereafter be heard, rather more faintly, in London, Moscow, Rio, and Tokyo. The impact's splash arrives at the East Coast not far behind the sound. In the deep sea, where it has plenty of room to expand, this mighty wave soon settles to a height of only fifty feet or so - a long, gentle swell moving inconspicuously but rapidly outward at a velocity of more than five hundred miles an hour. But tsunamis grow when water gets shallow. This one stacks up over the Grand Banks, then hits Manhattan at sunrise at a height of six hundred feet. Florida has already gone under. Before the day is out, most of Earth's low-lying regions have been submerged, from Edinburgh, Copenhagen, and Dubbn to Hong Kong and Bangkok Yet, in the final accounting, water creates only tertiary damage. A greater threat is fire. The conflagration begins within the hour, as a spectacular meteor shower best seen from Asia, where it is evening. Clumps of debris thrown into space by the exploding comet have been launched in all directions, Eke fleets of ICBMS, and now they descend, filling the night with fireballs. Many expire in the atmosphere, but millions hit, igniting forests, villages, and cities. Soon the world is ablaze, and the air turns black with soot. The soot, along with tons of talc-like dust pumped into the air by the explosion, clouds the atmosphere and blots out the sun for a period ranging from six months to a year, and it is this blackness along with an acid rain comprising sulfur dioxide and toxic metals-that proves to be the impact's most lethal agency. In a world gone dark that long, most plant Efe expires, as do marine creatures that dwell near the surface, and their loss, in turn, dooms the creatures that rely on them for food. The pattern of extinction shows a preference for the more complex organisms, which are most reliant on the support of multiple elements in the food chain. Human beings are complex organisms; their problem wiu be what to eat. With the world's food surpluses amounting, typically, to less than a year's supply, people who manage to survive the initial blast, floods, and fires wifl find themselves confronting starvafion. Among the dire possibilities brought forth by those who consider such things is the prospect that nuclear-armed nations with little remaining food might try to blackmail those with somewhat more food. In the over-all scheme of things, however, it doesn't matter much whether nuclear violence writes a final chapter to the general catastrophe. Scattered enclaves of humans might survive a major comet impact, but human civilization almost certainly would not.

Images of Shoemaker-Levy from the Hubble Space Telescope


"COMETS are vile stars," Li Ch'un Feng wrote, in the seventh century A.D. "Every time they appear ... something happens to wipe out the old and establish the new." To let one example stand for many, consider the great comet of 1680, moving like a ghost ship across the night sky, the sight of which occasioned expressions of hysteria. The theologian Christopher Ness warned that God had dispatched the comet as "a Sign from Heaven" that "signifies Drought, and portends War," and in Holland the philosopher Pierre Bayle complained that he was beset by the inquiries of terrified behevers who saw the comet as a sign "to give Sinners time to prevent by Repentance the Evils which hung over their Heads." But Edmond Halley saw it, too, from a ship on the English Channel, and when he reached France he met with the astronomer Jean-Dominique Cassini, and Cassini acquainted him with the idea proved by Isaac Newton, in his "Principia' that comets are interplanetary objects following predictable orbits, not missUes hurled without seaming by God, and that, indeed, several of the comets recorded in the annals of history might be recurring visits of the same comet. Halley confirmed this in 1705 by computing the orbit of the comet that has ever since borne his name and predicting that it would return in 1758 (as it did, sixteen years after his death). For this and other historical reasons, comets came to symbolize the distinction between the scientific-minded, who understood them to be peaceful plodders, and the ignorant and superstitious, who continued to shrink from them as portents of doom. (One of the few empiricists skeptical enough to have doubts on this score was Voltaire, who in 1738 noted in his "Elements of Sir Isaac Newton's Philosophy," a popular account of Newtonian mechanics, 'what a Disaster would it be for our Earth, if unhappily she should find herself in the same Point [as a comet]? The Idea of two Bombs, which burst on dashing together in the Air, is infinitely below what we ought to have of such an encounter as this.") When the first scientific academics were founded in France and England, in the seventeenth century, they were fervently concemed with differentiating empirically verifiable fact from superstition. Reports of stones falling from the skycoming, as they did, from folklore, ancient books, and the eyewitness accounts of the uneducated-were consigned to the realm of superstition. As the astronomer John Lewis notes, in his authoritative book "Rain of Iron and Ice," scientists of the day fefl into the trap of assuming that i, anything that was not already understood in physical terms must be superstitious nonsense. By the beginning of the nineteenth century, the extraterrestrial origin of meteorites had begun to gain acceptance among scientists, pardy because the high nickel content of metal-rich meteorites distinguished them from the rocks indigenous to the regions in which they were found, and pardy as a resldt of an imposing fall of more than two thousand stones in L'Aigle, Nonnandy, on Aped 23, 1803. That fall was investigated on behalf of the French Academy of Sciences by the great solar-system researcher Pierre-Simon Laplace, and the evidence persuaded him that the stones must have come from space. Even so, the notion that big stones hit occasionally, doing major damage, remained a hard sefl. Geologists attributed 91 the craters of the Moon to volcanoes, and craters on Earth likewise. Meteor Crater, a kilometre-wide hole in the desert near Winslow, Arizona, was only belatedly, after about 1929, recognized to be the work of a meteorite one that hit some fifty thousand years ago. Meteor Crater was the first impact site on Earth to be recognized as such. Other identifications followed. Typical was the case of Manicouagan, Quebec, a hundred kilometre ring where two lakes have been back-flooded by a hydroelectric dam. It remained unrecognized from the ground as a twelve-million-year-old impact crater, but its status was established through aerial photography, and it leaped out to the eye when it was viewed from orbit by astronauts and cosmonauts. More than a hundred and fifty terrestrial-impact craters have been identified to date, some of them in unexpectedly placid and setded places: the elegant manor house at Rochechouart, in the Vienne Valley of central France, is built of fragments of impact-breccia rock, which were melted together by an exploding meteorite a hundred and eighty-six million years ago and found in a crater twenty-three kflometres in diameter.

Shoemaker-Levy Comet impact on Jupiter

Yet the realization that impacts are ubiquitous in the solar system was slow to dawn. Not untl the nineteen-seventies and eighties, when the Mariner spacecraft returned images of the pockmarked surfaces of Mars and Mercury and the Voyager mission to the outer planets took detailed pictures showing thousands of overlapping craters on satellites of Jupiter and Saturn, did scientists come to appreciate that the solar system's topography resembles that of an artillery range. indeed, so extensive has meteor traffic been among the planets, with pieces coming to rest on Earth which had been knocked off the Moon, and Mars, and perhaps even Mercury, that if fife is found on Mars it may prove to be identical to life on Earth, thanks to primitive microorganisms' having long ago been ferried from Mars to Earth, or vice versa. Earth's relatively crater-free surface is the result of erosion: were it not for wind, rain, and geological upheavals Earth would look as pockmarked as the Moon. From decades of such reconnaissance has emerged a new and more sophisticated picture of the solar system as a unified entity with a common history. In this new picture, the planets owe their very existence to impacts. They are thought to have formed through the collisions of "planetesimals"-mile-wide objects, themselves built up from the dust grains and beachball-size clumps of material that orbited the infant sun in the early days. Earth, when young, was evidently hit by something as massive as Mars; the crash created a huge, molten splash of mostly surface material, and that material coalesced to form the Moon. The Moon itself bears the scar of at least one nearly catastrophic impact, in the form of a gigantic ringed crater, Mare Orientate, an ash-gray bull's-eye bigger than Sri Lanka. (Mare Orientate happens to point ninety degrees away from the Earth, so it remained undiscovered until it was photographed by lunar space probes. Had the Moon locked gravitationally to Earth a quarter of a turn later, so that Mare Orientale permanently faced us, we would have evolved looking not at the Man in the Moon but at a big, staring eye. How might that apparition have influenced the course of human history.) Eventually, the surviving planets emerged, having swept their orbits clear of everything massive enough to destroy them. There were, however, lots of pieces left over, and the great majority of these survivors are the comets. There are estimated to be a trillion of them, most of which belong to the Oort cloud. Named after Jan Oort, the Dutch astronomer who, just after the Second World War, first theorized its existence, the Oort cloud consists of a dark shell, centered on the sun, that starts beyond the orbit of Pluto, the outermost planet, and extends perhaps two light years into space, or halfway to the nearest star. Its comets remain serenely aloof, plodding, like tethered oxen, through immense orbits around the distant sun. But from time to time something-a passing star or cloud of gas, perhaps-knocks a bunch of comets out of orbit. Some climb to higher orbits, or escape the sun's gravitational field forever. Others head toward the inner solar system. For a comet to fall from its perch in the Oort cloud down to Earth's orbit can take a milhon years. Another, less populous school of comets swims closer to home, in a disk-shaped array called the Kuiper Belt (after Gerard Kuiper, of Yerkes Observatory). The largest Kuiper Belt comet yet observed, a two-hundred-kilometre-wide iceball called Chiron, pursues an unstable orbit that carries it inside the orbit of Uranus. Nobody yet knows how many Kuiper Belt icebergs exist, or how big they get. Some astronomers suggest that Pluto, which is icy, and is smaller than Earth's moon, and has an eccentric orbit, is not a planet at au but a Kuiper Belt object. As comets travel through the inner solar system, they leave behind snag trails of rocks and gravel. Earth encounters scores of comet trails every year, whereupon the debris, making a fiery entry into the atmosphere, produces what is known as a periodic meteor shower. During a meteor shower, if you stay up past midnight, when the night sky is on the bow side of Earth's orbital motion, you may see twenty to thirty meteors an hour. Occasionally, a rich shower will hurl down "shooting stars" faster than you can count them. The Leonid shower, which has generated spectacular fireworks at intervals of about a third of a century, is expected to peak again on about November 18, 1999, just in time to set off millennialist alarms. Each shower is a reminder that a comet once passed through here, and would have hit us had its timing been less fortunate.

Say Goodbye if Asteroid Hits

12th November 1996 LONDON -

Scientists are to discuss the threat posed by an asteroid hitting the Earth, amid claims the British Government is not awake to the risk and does not support an Australian early wanting project.

Experts believe the chances of being killed by an asteroid impact is four times higher than that of dying in a plane crash. An asteroid smaller than lkm across- smashing into Earth at 321cm per second would cause an explosion equivalent to more than 1000 of the most powerful hydrogen bombs yet detonated.

Scientists are taking,the danger seriously, and have set up observation teams to watch for Near Earth Asteroids (NEAs). But the early warning post set up in 1990 to cover the Southern Hemisphere, the Anglo-Australian Near Earth Asteroid Survey, is now under threat because its funding runs out at the end of the year. Dr Duncan Steel, who runs the observatory at Siding Spring in Australia, said no new funding had been offered by the British side of the partnership. Scientists will meet at the London headquarters of the British National Space Centre today to discuss the problem and the role Britain should be playing. Dr Steel said the British Government was "working from a position of profound ignorance" and did not understand the danger.

He said: 'Yes, people die monthly in plane crashes, but the numbers are thankfully small compared with the billions who would die in a major cosmic impact. "The probability of an asteroid or comet impact is small, but the consequences are horrendous. "People like to imagine that there are battalions of astronomers scouring the skies - there aren't. If a half-mile asteroid is due to hit us next week, you can expect six seconds' wanting. "When it enters the atmosphere it will light up like a thousand suns. By the time you've tumed to look at it, it will have struck the ground, releasing energy equivalent to 10 million times the Hiroshima bomb. Then it's goodbye." Dr Steel said Dr Tom Gehrels, leader of America's Spacewatch progranune which is tracking NEAs in the northern sky, had also identified the closure of the Australian project as a major backward step, and had written to British scientists and other interested parties. He added that Dr Edward Teller, the father of the hydrogen bomb, had written to the prime ministers of Britain and Australia expressing concern over the lack of action. PA

Is this the end of the world? New Scientist 12 July 1997 23

A SMALL comet striking Earth would create an explosion ten times as powerful as all the nuclear weapons in existence at the height of the Cold War, according to a supercomputer simulation. In a 48-hour calculation designed to test the new lntel Teraflops computer (named for its ability to perform a trillion operations per second) David Crawford of Sandia National Laboratories in Livermore, California, has modelled the impact of a billion-tonne comet smacking into the ocean.

Such a comet would be a mere ten-thousandth the size of Comet Hale-Bopp. But when it hit the virtual ocean (orange in the picture), it unleashed a massive explosion. Tidal waves washed over low-lying regions like Florida, and nearly 500 cubic kilometres of ocean vaporised instantly. This would fill the atmosphere with enough vapour to darken skies for months or even years, devastating world agriculture. A comet hits the Earth about once every 300 000 years. "It's a low-probability, high-consequence event," Crawford says. "if one did hit, your chance of becoming a victim would be high."

"All I am saying is NOW is the time to develop technology to deflect an asteroid"
New Yorker 8 June 98

Asteroid makes beeline for Earth
Mar 98
- An asteroid will pass close by the Earth in the year 2028 and could conceivably hit us astronomers warned yesterday. They said the asteroid, which had not been seen before, would pass as close as 42,000km to Earth. While chances of a collision were small, it would not be out of the question. "Chances are it will miss, us said Dr Brian Marsden of the International Astronomical Union (IAU) said. Even if it were on a path to hit Earth, technology might be available by then capable of deflecting the asteroid, he said. "If it were going to hit us, and that's a big if, we would have time to plan to do something about it," Dr Marsden said. The asteroid, which is estimatimated to be 1.6 km in diameter, has beep named 1997 XF11. It was discovered by Jim Scotti of the University of Arizona. Latest observations show it wit pass as close as 42,000km from the centre of the Earth. "It was quite startling to find to the nominal orbit we were using brought it as close as we did. I have, not seen anything like that," Dr Marsden said. Even if the asteroid passed by at 320,000km away, that would bring, it inside the Moon's orbit. Dr Marsden said calculations showed the asteroid would be closest at 18.30 GMT on Thursday, October 26, 2028 (7.30 am Friday October 27 New Zealand time). - "If it really is as close as 30,000 miles it will really be quite bright,' Dr Marsden said. It will be evening in Europe and will be visible there with the naked eye. An asteroid that slammed into the Earth 65 million years ago if believed to have knocked up so much dust that it wiped out the dinosaurs. Dr Marsden said the announcement was meant to alert astronomers, not to frighten the public.

Apocalypse Postponed New Scientist 21 Mar 98 AFTER a day-long drama, in which it seemed there was an outside chance that civilisation might end 30 years from now with a catastrophic asteroid impact, astronomers declared the all clear last Thursday. Revised calculations based on data from 1990 show that on 26 October 2028 asteroid 1997 XF11 should miss the Earth by 960,000 kilometres-2-5 times farther away than the Moon.

The inner solar system also contains millions of asteroids, of which fewer than one per cent have been located. An estimated half-million asteroids measuring a hundred metres or more in diameter pursue orbits that bring them close to Earth. One of the smaller and more numerous of these could smash every structure within three hundred miles of its impact site. A collision with one of the two thousand or so known larger ones, each the size of a small town, could wind back the clock of human civilization to the time of Vlad the Impaler. The realization that what we don't know can hit us began to gain strength in 1980, when the physicist Luis Alvarez; his geologist son, Walter; and a few of their colleagues at Berkeley identified iridium, an element rare on Earth but common in comets and asteroi 'ds, in a stratum that had been laid down at the time the dinosaurs died. Their theory that a comet's impact had wrought global death was resisted at first-especially by geologists, who were stiu preoccupied with volcanoes. But it is now widely accepted that a comet or an asteroid something like ten kilometres wide hit near Yucatdn sixty-five million years ago, wreaking enough havoc to doom the dinosaurs and nine-tenths of all other species. The "smoking gun" crater has been identified. It's centered near the port city of Progreso, Mexico, on the coast of Yucatdn, and hes pardy beneath the ocean. Though buried under nearly a mile of limestone, it turned up on seismic maps compiled by petroleum geologists, and has since been mapped by charting gravitational and magneticfield lines at the surface. The crater measures more than a hundred mdes in diameter. Glass globules thrown off by the impact have been found in contemporaneous strata in Haiti and elsewhere around the globe. The shape of the crater together with evidence of an ejecta-spray pattern suggests that the killer sailed in at an oblique angle of impact that spewed white-hot debris across North America. Research into what Carl Sagan called "the cold and dark' of a nudear winter helped clarify how explosions can do severe global damage by injecting dust and soot into the upper atmosphere.

Two impact splash 'craters' of Shoemaker-Levy

The copestone on the arch of potential catastrophe was laid on the night of March 23, 1993, during a routine observing run at Palomar by Eugene Shoemaker; his wife, Carolyn; and the amateur astronomer David Levy. The three had been surveying the sky for ten years, in order, as they put it, "to determine the nature and numbers of objects that crash into the planets and satellites and form craters." ... when Carolyn Shoemaker examined the flawed but usable exposed film, she saw a strange smear near Jupiter. It turned out to be a comet that had been trapped in an orbit around Jupiter, probably in 1929 or so, and then had recently been torn into fragments byjovian tidal forces, resulting in what looked like a string of pearls. Paul Chodas was alerted by Brian Marsden to calculations by a Japanese amateur astronomer named Syuichi Nakano which suggested that the newly named Shoemaker-Levy was destined to hit Jupiter. When Chodas, at the Jet Propulsion Laboratory, ran his impact prediction program, the results startled him. "I'd always seen zeros before," he reca-fled. "Suddenly a fifty-per-cent number came up." ... And that is just what happened, sixteen months later. Starting on the night of July 16, 1994, the icebergs trundled in, one after another, like trucks skidding to a pileup, and exploded in Jupiter's upper atmosphere in extravagant, rising fireballs that left the giant planet's salmon and sand-colored atmospheric bands scarred by a chain of lurid black splotches that endured for weeks. Scientists gaping at this unprecedented sight began taking the threat of comet impacts more seriously. ... Here we are, close to the edge, protected from the true immensity of the universe by a thin blue line. A day will surely come when the sheltering sky is torn apart with a power that beggars the imagination. lt has happened before. Ask any dinosaur, if you can find one. This is a dangerous place."

Collision impact on Jupiter


THE good news about death from above is that the odds against its happening are steep. Earthshaking impacts like the one near Yucatan are estimated to occur only about once in a hundred million years. Encounters with comets and asteroids a kilometre or so in diameter, sufficient to destroy a country the size of India, occur about once in a million years. A thousand years or so typically pass between hundred-metre objects, which could take out a city but would pose no obvious threat to Earth as a whole. But even if these statistics are accurate-and, after all, they are based on incomplete knowledge of our solar system - to declare that disaster strikes Earth, on average, only once in a thousand years does not mean that we are guaranteed a thousand-year interval between disasters. As Tom Gehrels of the University of Arizona has noted, "the very small chance of it happening tomorrow is just as great as a million years from now." just last fall, on November 22, 1996, a meteor hit near San Luis, in western Honduras, excavating a crater a hundred and sixty-five feet wide and setting fire to acres of coffee plants. It missed taking out downtown Bangkok or Manila by about ten hours. We're constantly being bombarded by smaller objects. Every hour, the Earth puts on a ton of weight in the form of micrometeoritic dust: run a damp sponge across a bookshelf, and you pick up a few bits of defunct comets, of grime ground off colliding asteroids, and of powder left behind when the planets formed. Meteors the size of peas can make an eye-opening streak across the night sky before burning up in Earth's atmosphere. Fist size ones may survive their fiery passage and hit. This happens, somewhere on Earth, about once every two hours. Occasionally, a meteor seen streaking across the sky is subsequently found on the ground. Locating one normally requires hard work or else luc pieces of a meteor that exploded about thirty kilometres above Revelstoke, British Columbia, on the night of March 31, 1965, might have soon been lost beneath fresh snowfalls if two fiir trappers hadn't come upon the site a couple of weeks later. A few meteorites (a meteorite is a meteor that hits Earth) arrive in a more convenient, if more threatening, fashion. On the evening of Friday, October 9, 1992, thousands of people in the northeastem United States, many of them watching high-school football games, saw a brilliant meteor streak overhead. It broke up in the air. Moments later a twenty-eightpound chunk of it smashed the night rear fender of a 1980 Chevy Malibu parked outside the home, in Peekskill, New York, of an eighteen-year-old highschool senior named Michelle Knapp. She heard the crash, ventured out, and found the meteorite, "still warm to the touch," resting in a crater beneath the gaping hole it had punched in the car. (Miss Knapp sold the meteorite, dassed an "ordinary chondrite," to a collector for a reported fifty-nine thousand dollars; the car, which she had purchased for a hundred dollars, brought ten thousand dollars from a private museum. There's a bull market in meteorites these days.) Reports of meteorites damaging houses are fairly rare, yet two homes in a single community were hit within a period of eleven years.

THE growing appreciation of the hazards of an impact has already altered conceptions about our relation to the wider solar system. Overturned for good is the assurance that, as generations of textbooks and newspaper articles have habitually put it, "no one in recorded history has ever been killed by a meteorite." Consider tsunamis, the so-called tidal waves that have killed millions of the residents of low-lying coastal re 'ons. Tsu91 namis can be touched off by undersea earthquakes, or by volcanoes, as when Krakatoa, in Indonesia, blew up, on August 27, 1883, with a force estimated at more than a hundred megatons, generating a wave that sank whole fleets of riverboats at Calcutta, two thousand miles away, and re 'stared on tide gauges in the 91 Enghsh Channel. Tsunamis of unknown origin have routinely been attributed to earthquakes and volcanoes. But calculations done byjohn Lewis and others indicate that large meteorites-most of which slam into the oceans, since most of Earth's surface is water-must also have set off deadly tsunamis. "Over time scales of one hundred thousand years and longer," Lewis writes, "the greatest tsunami waves produced on Earth must be from cosmic impacts." This hypothesis can be tested by looking for extraterrestrial materials mixed into the bathtub rings of debris deposited high above sea level by tsunamis in the past, but none has yet been so examined. Extrapolating from data adduced by counting craters on the Moon and planets, Lewis has run computer simulations of the fatalities Ekely to have been occasioned by cosmic impacts on Earth in the course of the twentieth century (which he chose because we have reliable information about the distribution of human populations during that time). The results, though tentative, are sobering. In the first test run that Lewis reports on, more than a hundred people are killed and a thousand injured by an impact tsunami. "But no connection is made between the (unobserved) impact and the casualties," he wn'tes. "Experts report'no hazard from meteorites.' " Scientists, having acquired a new sensitivity to the impact hazard, have begun to look at historical records with a freshly baleful eye. New significance is being discerned in texts as remote as the ancient Egyptian "Tale of the Shipwrecked Sailor" (circa 2000 B.C.), in which a sympathetic spirit in the form of a giant snake bemoans the loss of his family"A star fell and they were gone, gone up in flame ... afl burned." The Biblical tale of the Seventh Seal has likewise taken on a tincture of astronomical significance. Chapter 8 of the Book of Revelation reads, "And the third angel sounded, and there fell a great star from heaven, burning as it were a lamp, and it fell upon the third part of the rivers, and upon the fountains of waters. Many men died of the waters, because they were made bitter.... The third part of the sun was smitten, and the third part of the moon, and the third part of the stars; so as the third part of them was darkened, and the day shone not for a third part of it, and the night likewise. A,nd I beheld, and heard an angel flying through the midst of heaven, saying with a 16ud voice, Woe, woe, woe, to the inhabiters of the earth." Indeed, the catastrophic associations of the Biblical phrase "fire and brimstone" may have their origin in the fact that meteors are typically rich in sulfur, for which the archaic word is brimstone. As with literature, so with historical records. One reads with newfound apprehension that a bolide-an especially bright meteor-exploded over Constantinople on a clear afternoon in 472 A.D., hitting the city with a wave that knocked sailboats flat in the water and rained down black dust; or that on the night of June 25, 1178, according to a report by a monk named Gervase, at Canterbury, England, there was a flash on the crescent Moon that "was repeated a dozen times or more," leaving the Moon with "a blackish appearance." The meteor scholar Jack Hartung identifies this event with a hundred-and-twenty-thousandmegaton explosion that carved out the young lunar crater Giordano Bruno. Nor are all the tales of hits and near misses so remote in time. On June 30, 1908, an incoming comet or asteroid exploded over the Tunguska region of Siberia, with a blast that flattened trees for fifteen kilometres around and blew enough debris into the atmosphere to cause "white nights," which mystified Europeans, no news reports having reached them from horrified eyewitnesses in the Siberian forest.

Almost once a month, a comet or asteroid detonates at high altitude with the force of a kiloton or more of TNT, but these explosions occur too high to do any damage, so quickly and unpredictably that few are seen by human beings. The flashes are often observed, however, by orbiting mihtarry surveillance systems, such as the Defense Support Program's DSP-647 satelEtes. The Defense Department used to throw away data on bolides once it had been determined that they weren't the enemy bombers or the missiles that the system was built to detect, but recently, in response to the pleas of scienfists, the govemment has begun releasing such information. Hence we know, for instance, that on February 1, 1994, there was a hundred-kiloton explosion-ten Hiroshimas-over the Marshall Islands, in the western Pacific. It flashed brighter than the sun, but was evidently seen by only a few fishermen.

The 10 kilometre diameter asteriod Yucatan impact which wiped out the dinosaurs
65 million years ago may have caused more damage because of its glancing impact
(New Scientist 12-9-96 14)


ONE of the problems with attempting to estimate the chance of a collision is that our interplanetary environment changes over time. The threat from comets, for instance, is greater than average during comet-shower periods, when squadrons of comets dislodged from the Oort cloud come hurtling into our neighborhood; some astronomers think we're in a comet shower today. The case for taking the danger seriously was made in a NASA study of near-Earth objects: "Although, statistically speaking, the risk of major impacts in the near filture is low, the possible consequences are so vast that every reasonable effort should be encouraged in order to minimize them." So what do we do? The first step, astronomers agree, is to take a census of everything out there that is big enough and close enough to threaten us. Oddly, this has not yet been done. One might think of astronomers as scanning the skies, like lookouts on shipboard, but in reality most professional astronomers scrutinize tiny pieces of sky and seldom do any scanm'ng at afl. Big telescopes have fields of view too narrow to embrace a major lunar crater, much less sweep the heavens for comets and asteroids. Wide-field telescopes can do the job, but they are customarily assigned to other duties. Skyscanning is left mainly to amateurs, and to a few offbeat professionals, Eke Gene Shoemaker. David Morrison, who has the delightful title "director of space" at the NASA Ames Research Center, likes to say that the number of people searching for threatening astronomical objects is 11 smaller than the staff of one McDonald's restaurant." Collectively, this little band discovers two or three Earth approaching asteroids every month-a useful contribution but not enough to make any considerable dent in our ignorance. Extrapolating from such findings, and from the cratering rates of the Moon and other satellites, scientists cal culate that about two thousand asteroids larger than a kilometre in diameter-big enough to generate devastating tsunamis and threaten "nuclear winter"-cross Earth's orbit. To date, only about a tenth of them have been located.

Asteroids are hard to see, and detecting those as small as a hundred metres in diameter the ones capable of leveffing a city may take time, even with a more sophisticated search effort. Nor would such a search warn us of the rarer but potentially more lethal long-period comets: an early-warning system capable of detecting those in time might require that sensors be deployed beyond the orbit of Jupiter. Meanwhile, we remain in the dark, subject to unwelcome surprises like the advent of Asteroid 1994 YM1, a tumbling, house-size boulder that was discovered only one day before it flew past Earth at a distance of only sixty-five thousand miles. "Such'near hits'probably happen once or twice a week," Lewis says, "but pass unnoticed because there is no large-scale survey of the skies going on to seek them out." If an asteroid or short-period comet should be discovered to pose a threat to Earth, what could be done to stop it? The answer depends upon several things, including the object's mass: not surprisingly, the bigger, more dangerous ones are harder to move around than the little ones. But the most important consideration is how much warning time we'd have. If impact was years away, many options would be available. We could, for instance, land a probe on a threatening asteroi 'd and use the probe's rocket motor to alter the asteroid's orbit into a safer path. If, however, the warning fime was shortand for an incoming comet it could be only a matter of months-the sole recourse might be a high-powered interceptor rocket armed with a bomb powerful enough to blow it off course.

From such considerations it came to pass one dark night in 1994 that Edward Teller, known as "the father of the hydrogen bomb," found himself in the front seat of a bus speeding down a remote highway east of the Urals, his face illuminated by the flashing blue lights of a police escort, on his way to the Russian Federal Nuclear Center at Snezhinsk, better known as Chelyabinsk-70. ... As he said soon after the Chelyabinsk meeting, we are very sick, I have a cure, and my only concern is to achieve overkill." Other scientists had been quick to object to Teller's injecting nuclear weapons into the previously pacific field of asteroid research, and Teller soon retreated to the position that conventional explosives could do the ob. But by that time he was deeply embrohed in a debate with several researchers, Carl Sagan among them, who feared that even a non-nuclear "cure" would be worse than the disease. Clark Chapman, an astronomer of the Southwest Research Institute in Boulder, Colorado, denounced Teller's proposals as "radically more expensive and dangerous than the modest threat they would address." Others argued that even a non-nudear deflection system, if it fefl into the hands of a maniac, could be used to redirect a previously benign comet or asteroid into a collision course with Earth. Deflection "is a double-edged sword," Sagan and a colleague wrote in the journal Nature. "If we can perturb an asteroid out of impact trajectory, it follows that we can also transform one on a benign trajectory into an Earth-impactor." ... Many physicists have forgiven Teller neither for what they see as his betrayal of Oppenheimer nor for his devotion to secret weapons research. He remains defiant, warning that by cutting the funding of weapons "we are rushing into a third world war by means of disarmament," and he delights in repeating deliberately unsettling utterances hke, "A bttle radiation can be good for you." ... I asked Teller about critics who charge that his enthusiasm for intercepting near-Earth objects is technologically driven-that he's looking for a mission that would both "save the world" and rescue his laboratory from fiirther budget cuts through the application of technology developed for the Strategic Defense Initiative. "Surely it has occurred to you that S.D.I. technology might be applied to this problem," I ventured. "Anything can be applied to anything else," Teller rephed. "It is only in this sense that I agree with you. I say that we are now both tamng about utter nonsense." ... I asked Teller about the Sagan objecfion that an asteroid-deflection system might be more dangerous than the asteroids are. "To my mind, this makes no sense at all," Teller replied. "If I want to do damage in Moscow, there are a million ways how to do it more easuy than to deflect an asteroid. If somebody wants to try such a thing, he has to do it practically publicly. It would be difficult, practically impossible, to keep secret, and such a thing can be worried about only by people whose main purpose in hfe is to worry."

Carl Sagan did not look worried when I talked with him about asteroids, over breakfast in a restaurant in Washington, D.C., but he did look frail. He had undergone bone-marrow therapy for myelodysplasia, a rare blood disease, and the procedure had cost him his hair and left his skin the color of rice paper. But his latest test reports were all nominal, and he had no reason to anticipate the sudden reversals that would lead to his death, from pneumonia, only five weeks later. "The Cold War is over, and at best there is funding for maintaining a small arsenal of a few thousand nudear weapons instead of a few tens of thousands of weapons," Sagan said. "That just isn't enough to maintain the fidl weapons estabhshments at the Livermore, Los Alamos, and Sandia laboratories, much less at Chelyabinsk-70 and the corresponding Chinese center. So for those guys the threat of impact is a godsend. We're told that we need to develop nuclear weapons to deflect those comets and asteroids that might hit the Earth-a whole new enterprise, called planetary protection. Who could object to that? Protecting the entire planet, independent of race, religion, creed, or national origin. "For a while, Edward Teller was saying that we needed to develop weapons of a much higher yield than had been developed hereto, because that's what you need to pulverize a large near-Earth object. But it was soon realized that deflecting is more efficient than pulverizing. You give it a little nudge at perihelion, when the object is at its closest distance to the sun. And that htde nudge at perihelion makes a big miss of the Earth later on in the orbit." ... Whatever kinds of weapons you're going to use to deflect or disintegrate, you have to test them long in advance. You wouldn't want an untested weapon. And so, in his view, we have to go into an operation mode right away with missiles and nuclear weapons. "That breaks three international treaties that we are signatories of the Outer Space Treaty, the hmited test-ban treaty, and the Anti-Ballistic Missile Treaty. But the thing that really worries me is that if you had this capability, then a madman, or somebody just making a stupid error, could deflect an asteroid so that it hit the Earth. The chances are, of course, low. There would be safeguards. People would be looking over each other's shoulders, naturally. But, remember, this is a case where people are worried about an accident whose probability is one part in a hundred thousand, the accidental hitting of the Earth. Can they be sure that there's no chance of one in a hundred thousand of a madman taking over a modem industrial state? Or some religious fundamentalist wishing to bring about the Apocalypse? ... It's not out of the question that somebody in control of a modern industrial state, in a situation of great emotional stress, might be perfectly happy to destroy a country, or a region, or the planet."

Comets really can "wipe out the old and establish the new," as Li Ch'un Feng had it long ago. The impact that killed the dinosaurs cleared ecological room for the explosive radiation of new lifeforms, our distant ancestors among them. The human species is much too young to have any cultural memory of that ancient disaster, but perhaps a smaller yet still noxious comet hit more recently, in prehterate times, when there were people around to suffer the consequences and teu stories about it. Current studies indicate that there must have been at least one ten-gigaton impact within the past seventy thousand years - a horrific blast, which would have blacked out the sun, flooded much of the world, drenched the land with fire and the smell of brimstone, and otherwise brought down a whole Biblical apocalypse. And it seems reasonable to assume that the poets and storytellers of the day would have sought to preserve the memory of so dreadful an event, without concerning themselves overmuch with whether professors of the future were destined to poke filn at their tales. If so, the realization that comets and asteroids can put us in harm's way is not just bright new knowledge but also a species of remembrance.

Carl Sagan Pale Blue Dot ... on asteroid control

In principle, you could use big rocket engines, or projectile impact, or equip the asteroid with giant reflective panels and shove it with sunlight or powerful Earth-based lasers. But with technology that exists right now, there are only two ways. First, one or more high-yield nuclear weapons might blast the asteroid or comet into fragments that would disintegrate and atomize on entering the Earth's atmosphere. If the offending worldlet is only weakly held together, perhaps only hundreds of megatons would suffice. Since there is no theoretical upper limit to the explosive yield of a thermonuclear weapon, there seem to be those in the weapons laboratories who consider making bigger bombs not only as a stirring challenge, but also as a way to mute pesky environmentalists by securing a seat for nuclear weapons on the save- the-Earth bandwagon. Another approach under more serious discussion is less dramatic but still an effective way of maintaining the weapons establishment-a plan to alter the orbit of ally errant worldlet by exploding nuclear weapons nearby. The explosions (generally near the asteroid's closest point to the Sun) are arranged to deflect it away from the Earth [contrary to the Outer Space Treaty signed by US and Russia prohibiting weapons of mass destruction in space]. A flurrry of low-yield nuclear weapons, each giving a little push m the desired direction, is enough to deflect a medium-sized asteroid with only a few weeks' warning. The method also offers, it is hoped, a way to deal with a suddenly detected long-period comet on imminent collision trajectory with the Earth. The comet would be intercepted with a small asteroid. (Needless to say, this game of celestial billiards is even more difficult and uncertain - and therefore even less practical m the near future-than the herding of an asteroid on a known, well-behaved orbit with months or years at our disposal.)

We don't know what a standoff nuclear explosion would do to an asteroid. The answer may vary from asteroid to asteroid. Some small worlds might be strongly held together; others might be little more than self-gravitating gravel heaps. If an explosion breaks, let's say, a 10-kilometer asteroid up into hundreds of 1-kilometer fragments, the likelihood that at least one of them impacts the Earth is probably increased, and the apocalyptic character of the conseqences may not be much reduced. On the other hand, if the explosion disrupts the asteroid into a swarm of objects a hundred meters in diamieter or smaller, all of them might ablate away like giant meteors on entering the Earth's atmosphere. In this case little impact damage would be caused. Even if the asteroid were wholly pulverized into fine powder, though, the resulting high-altitude dust laiyer might be so opaque as to block the sunlight and change the clmiate. We do not yet know.

A vision of dozens or hundreds of nuclear-armed missiles on ready standby to deal with threatening asteroids or comets has been offered. However premature in this particular application, it seems very familiar; only the enemy has been changed. It also seems very dangerous.

The problem, Steven Ostro of JPL and I have suggested, is that if you can reliably deflect a threatening worldlet so it does not collide with the Earth, you can also reliably deflect a harmless worldlet so it does collide with the Earth. Suppose you had a full inventory, with orbits, of the estimated 300,000 near-Earth asteroids larger than 100 meters-each of them large enough, on impacting the Earth, to have serious consequences. Then, it turns out, you also have a list of huge numbers of inoffensive asteroids whose orbits could be altered with nuclear warheads so they quickly collide with the Earth.

Suppose we restrict our attention to the 2,000 or so near- Earth asteroids that are a kilometer across or bigger-that is, the ones most likely to cause a global catastrophe. Today, with only about 100 of these objects catalogued, it would take about a century to catch one when it's easily deflectable to Earth and alter its orbit. We think we've found one, an as-yet-unnamed asteroid so far denoted only as 19910A. In 2070, this world, about I kilometer in diameter, will come within 4.5 million kilometers of the Earth's orbit-only fifteen times the distance to the Moon. To deflect 19910A so it hits the Earth, only about 60 megatons of TNT equivalent needs to be exploded in the right way - the equivalent of a small number of currently available nuclear warheads.

Now imagine a tinie, a few decades hence, when all such near-Earth asteroids are inventoried and their orbits compiled. Then, as Alan Harris of JPL, Greg Canavan of the Los Alaillos National Laboratory, Ostro, and I have shown, it niight take only a year to select a suitable object, alter its orbit, and send it crashing into the Earth with cataclysnilc effect.

The technology required-large optical telescopes, sensitive detectors, rocket propulsion systenis able to lift a few tons of payload and make precise rendezvous in nearby space, and thermonuclear weapons-all exist today. Improvements in all but perhaps the last can be confidently expected. If we're not careful, niany nations may have these capabilities in the next few decades. What kind of world will we then have made?

We have a tendency to minimize the dangers of new technologies. A year before the Chernobyl disaster, a Soviet nuclear power industry deputy niinister was asked about the safety of Soviet reactors, and chose Chernobyl as a particularly safe site. The average waiting time to disaster, he confidently estiniated, was a hundred thousand years. Less than a year later ... devastation. Similar reassurances were provided by NASA contractors the year be- fore the Cli Ile iger disaster: You would have to wait ten thousand years, they estimated, for a catastrophic failure of the shuttle. One year later ... heartbreak.

Carl is right to be very careful. However society is far more fragile than the biosphere, even despite our assaults. A much smaller disruption would end society as we know it and hence a more frequent one. To protect both ourselves and the biosphere we live in from major species extinction we need to protect against large impacts on earth peacefully. Perhaps disarmament could be an integral part of planning for constructive use.

This Could Prove to be the Greatest Act of Folly ever Perpetrated
Wilson da Silva, Canberra New Scientist 12-Oct-96.

THE first truly global effort to detect and track thousands of asteroids with the potential to strike the Earth is about to crash just as it was getting off the ground. The asteroid watch programme for the southem skies, run by three Australian astronomers, will come to a halt at the end of the year when funding from the Australian government runs out. This programme is an essential part of the international project.

Duncan Steel, who runs the Australian asteroid tracking programme, told the ANZAAS meeting that the average risk of being killed by an asteroid strike is 1 in 5000. This figure is based on an asteroid at least a kilometre wide crashing into the Earth, an event that is estimated to happen once every100,000 years. When it does happen, however, the death toll is so high that it skews the odds. But a much smaller object slamming into the biggest target on Earth - the Pacific Ocean - could devastate the countries of the Pacific Rim. "You only need a 100 to 200-metre object, even if it blew up in the atmosphere over the Pacific, to generate a blast wave that would cause a tsunami 100 metres high with a range of 1000 kilometres," said Steel. "It would spread out and wipe out every single city in the Pacific Rim. The chances of that occurring in the next century are better than 1 in 100." The Australian tracking programme consists of three nights of observation a month with the Schmidt wide-aperture telescope at the Siding Spring Observatory in New South Wales. Once they spot an asteroid, the Australians notify the International Astronomical Union's Minor Planet Center in Cambridge, Massachusetts, which passes on the information to other programmes in the northern hemisphere. Other astronomers then track the asteroid during their night, helping to build up an accurate picture of its orbit. When northern observatories discover a new asteroid, they notify the Australians, who track it during their hours of darkness. The Australians have discovered 10 per ould cent of all Earth -crossing asteroids since the programme began in 1990, and are responsible for a third of all the asteroid tracking data produced. The University of Arizona has run an asteroid tracking programme in tandem with the Australians for several years, while a multi-million dollar joint project between the US Air Force and NASAs Jet Propulsion Laboratory has just started up in Haleakala on the Hawaiian island of Maul. But now the Australian funding - which amounts to just $50,000 a year - is being withdrawn. Steel says he would prefer not to be running the programme at all. He believes it should be the responsibility of the defence department. Either way, the worldwide effort is now in danger of falling apart because of Canberra's short-sightedness, he said. The Australian government, determined to reduce its budget deficit, has trimmed science programmes across the board. "If, having realised the danger is there, we do not take steps to ascertain whether an impact is due within the next century, this could prove to be the greatest act of folly ever perpetrated by humankind."

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