Cosmic Catastrophes

June 2003

Cosmic Catastrophes Science Fiction or Reality? by Dr. Thomas Grollmann

m ted fro Reprin No. 11 Topics

Dr. Thomas Grollmann is a geophysicist with a special interest in the atmosphere and climate issues. He has been with GeneralCologne Re for 10 years as an expert in the field of natural hazards and has led the Cat Modeling team within the Cat Center of Excellence since 2001. The primary focus of his work is on

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developing and checking the plausibility of models for the natural hazards of earthquake, windstorm and flood in order to determine the potential losses and average required risk premium per year on a worldwide basis. In this paper, he discusses a hazard that has still to be modeled but which entails a considerable loss potential.

An asteroid measuring 50 meters in diameter hurtles towards the earth at a speed in excess of 55,000 kilometers per hour. The object approaches the earth from the side illuminated by the sun and therefore aviods detection by any observatories on account of its apparently stationary orbit. Friction with the atmosphere rapidly heats the object so vigorously that it begins to glow more brightly than the sun. It passes almost silently through the atmosphere, accompanied by intense thermal radiation. Electronic control systems for railways, industrial facilities and computers are severely disrupted. The bow wave created in front of the object decelerates it so sharply that shortly thereafter it explodes in the air with the force of 1,000

Hiroshima bombs - little remains other than gas and dust. The flash of light can be seen over a radius of 1,000 kilometers. The heat wave is so powerful that people on the ground feel as if they are being burned alive. The air-pressure wave caused by the explosion hits shortly afterwards - first a deafening bang, then a burning hurricane that sweeps away everything in its path. Forests are left in flames, gas stations explode, everything within a radius of 30 kilometers is incinerated. The next air-pressure wave extinguishes the bulk of the fires but also snaps trees, blows out windows and doors, and indeed flattens entire houses. Since the shock wave spreads more

quickly through the ground, it is heralded by minor earth tremors. Power supplies and communication channels are cut. Several thousand deaths are reported, more than 100,000 people are left injured and over 2,000 square kilometers of urban land and forest are devastated - an area twice the size of Berlin. Science fiction or reality? In a way, both. Although the probability of such an event occurring over a major city is undoubtedly small, the possibility of an object of this size impacting somewhere on earth is greater than generally assumed. Many such impacts have occurred in the past, one of the most well known

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Comets and Their Composition Comets are chunks of ice that consist primarily of water ice, frozen gases, dust and carbon compounds - hence the frequently used description of a “dirty snowball.” They are believed to originate in an area in the outer solar system between Uranus and Neptune. Hot gases moving outwards can cool here and form solid bodies. As the planets formed, these objects were pushed outwards by the

force of gravity and are now located in the so-called Oort Cloud. When its path is disrupted by other stars, a comet can leave its original orbit and crash inwards onto a planet, such as the earth. As the comet draws closer to the sun, solar radiation heats up the comet’s surface and some of the ice vaporizes - giving rise to the tail. Depending on their orbit durations, comets are divided into short-period - less than 200 years - and long-period comets

- more than 200 years to several million years. The comets move in elliptical orbits around the sun, short-period comets in the same plane as the planets and long-period comets on any path. The total number of comets in the Oort Cloud is estimated to be 100 billion, of which at least one million can reach the inner solar system. Due to the considerable distance, it is impossible to determine how large the objects in the Oort Cloud are. A further

Asteroid belt. Located between Mars and Jupiter, the asteroid belt is a dense cloud of around 50 million objects (above).

being the asteroid strike in the Siberian taiga in 1908. Survivors of that disaster described a scenario similar to the one outlined above. The aftereffects could be seen locally for years, indeed decades, afterwards. So are meteorite strikes a real risk, and is this another hitherto unrecognized hazard like the terrorist attacks of September 11? Is there evidence of historical impacts on earth, and if so, how are we to imagine such events might unfold? How can we prepare for them, and what steps should we take to avoid being caught by surprise the next time?

The comet Kudo-Fujikawa passing in early 2003.

January 12, 2003 January 16

Earth

January 20

Venus

January 24

Sun

Mercury January 28 February 1, 2003 February 5

February 9

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comet reservoir located outside Neptune’s orbit, the EdgeworthKuiper Belt, is named after two planetary researchers. Objects with a diameter of 200 - 400 kilometers have occasionally been observed there. The comets in this belt are difficult to discover since the sunlight is too weak to vaporize the ice on account of the vast distance.

Mars

Before considering these questions, let us first shed some light on the origin of the intruders, their prevalence, the effects they have on the earth and ultimately the consequences for the insurance industry.

Asteroids Asteroids, also known as small planets, planetoids or meteoroids, have little ice content compared to comets, or even none whatsoever. They are composed largely of rock with small amounts of metals and carbons. A small proportion of asteroids, around 3%, is comprised almost entirely of metals, most commonly iron. The main belt in which asteroids orbit the sun on almost circular paths is located between the planets Mars and

Jupiter. The total mass of the asteroids is less than one per mil of the earth’s mass. Near-earth asteroids (NEOs) at a distance of less than 7.5 million kilometers and with a diameter in excess of 150 meters are categorized as potentially hazardous asteroids (PHAs), since disturbances in their orbit could cause them to come closer to the earth. Of the currently known 1,500 NEOs, one-third are classed as PHAs. Objects smaller than 30 meters in size would burn up in the atmos-

Earth

Origin and Classification of Extraterrestrial Objects Approximately 4.6 billion years ago, the compression of an original cloud of gas and dust gave birth to our solar system. Collisions between the first bodies of solid rock ultimately caused the planets and their moons to form. Yet some fragments of rock were left behind to find another destiny - not as planets or moons, but as comets and asteroids. Celestial phenomena such as comets were long regarded as messengers of the gods or as part of the planetary system. As long ago as 1695, however, the planetary scientist Edmond Halley realized that comets orbit the sun - Halley’s Comet, named after him, was correctly identified as having a return period of 76 years. Initially, the search for further planets and comets was restricted to the

phere and therefore pose no danger. Of the estimated 50 million objects, only around 1,500 are known to be earth-near. Currently estimated number of near-earth asteroids: Size

Number

> 30 m

> 50,000,000

> 100 m

> 320,000

> 500 m

> 9,200

> 1,000 m

> 2,100

> 2,000 m

> 400

Sun

Mars

orbit parameters specified by Newton in his theory of gravitation. In this way, it was possible on the basis of disturbances affecting already known planets to predict the existence of other planets - the planet Uranus, for example - which were only discovered years later. It is only in the last 50 years that comets have been systematically traced and cataloged. Many comets are to be found in the so-called Oort Cloud - a comet reservoir that came into existence after the planets were formed. Located in the outer solar system, it forms a spherical cloud around the sun. The Edgeworth-Kuiper Belt, another comet reservoir named after two planetary scientists, is located outside the orbit of Neptune. Individual objects with a diameter of 200 - 400 kilometers have occasionally been sighted there.

Jupiter

Comets in this belt are very difficult to detect, however, because at this distance the sunlight is too weak to vaporize the ice. Comets move around the sun in elliptical orbits. Short-period comets with orbit durations of less than 200 years move in the same plane as the planets, but longperiod comets with return periods of hundreds of thousands or even millions of years come from every direction. Long-period comets are particularly difficult to track, since they often remain undiscovered due to their long orbit durations and cannot be located until they are in the vicinity of Jupiter. An impact on the earth would then only be around three to four more years away - short notice for possible defensive measures. Given the large number of objects, it is virtually impossible with the tools cur-

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rently available to calculate in advance the precise path of every comet and the moment when each one will appear in our solar system. Yet there are also other objects too small to be classified as planets. These are known as asteroids, the largest of them - Ceres - having a diameter of 931 kilometers. Since these objects are too small to be seen with the naked eye, they were discovered relatively late, with the first being identified in 1801. Asteroids consist primarily of rock with metal and carbon admixtures. Meteorites composed of iron are found more rarely. Today, more than 150,000 of these “mini-planets” have been detected, although the precise path of such asteroids is known in only about 20% of cases. For the most part, these small planets travel around the sun in nearcircular orbits in the so-called asteroid belt between Mars and Jupiter - moving in the same plane as the other planets. Several asteroids intersect with the earth’s orbit. These are referred to as “near-earth objects” (NEOs). Others which do not currently cross the earth’s path could be nudged out of their original orbit and crash into the earth. The catastrophic scenario used in films, whereby a comet hits an asteroid and redirects it towards the earth, is pure fiction, since such a collision would destroy both objects. The largest of the more than 400 currently known NEOs are approximately eight kilometers in size, while the vast majority of NEOs measure between one and three kilometers. The composition of meteorites differs fundamentally from rocks found on earth. During the long period they spend travelling through space, mete-

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orites are constantly bombarded by cosmic radiation. This gives rise to nuclear reactions, which create a number of isotopes with known half-lives. On this basis, it is possible to determine how old meteorites are. They range in age from a few million years to 4.55 billion years, the age of the earth. Each year, approximately 40,000 tons of micrometeorites fall to earth - roughly 25% of the total extraterrestrial material that reaches the earth on a long-term annual average. This corresponds to around 50,000 meteorites per year. In other words, the earth is struck by meteorites very frequently.

Signs of Impact on the Earth How can we distinguish between impact craters and volcanic craters or other crater-like formations? On the earth, unlike on other planets, there are many processes which in the long run cover over the traces of an impact and indeed render them unrecognizable: erosion, sedimentation and continental drift. In a relatively short space of time, erosion due to water, wind, sandstorms, glacier formation and temperature changes eats away at exposed surfaces such as crater rims and ultimately levels them off. Sedimentation deposits the eroded material in lower-lying areas inside or around the rim of the crater, thus filling in the topographical irregularities. It is due to these surface-changing processes on the earth that, for example, small craters such as the Meteor Crater in Arizona have become virtually unrecognizable following the erosion of 100-200 meters of rock. The famous impact crater in Mexico, which - based on our current knowledge - is believed to have been caused 65 million years ago by an asteroid and

heralded the extinction of the dinosaurs, could only be identified with certainty using aerial photographs and subsequent seismic, magnetic and gravimetric measurements. An impact at sea can cause the formation of craters that do not project up to the ocean’s surface. If an asteroid is large enough (> 1 km), the object can penetrate the earth’s crust to a considerable depth. This may induce instability in the crust and cause volcanoes to form. New islands are created at the impact site, leaving the impact itself undetectable. Even if there is no volcanic activity, sedimentation covers over the impact crater relatively quickly. In the course of millions of years, continental drift (also referred to as plate tectonics) modifies the appearance of the earth’s surface; the shape and structure of craters are changed or entirely destroyed as entire plates disappear and dissolve into the earth’s mantle, are distorted by tectonic processes or are forced upwards into mountain ranges as they collide with one another. Identification of impact craters is consequently no longer possible. Since it is clearly difficult to identify craters on the earth, it is worth making comparisons with other planets and moons where the forces of erosion either do not exist or are less severe. Virtually all the craters on the moon were caused by impacts. Owing to the lack of an atmosphere, even the smallest fragments measuring just millimeters - crash into the moon’s surface with a high velocity. On the earth, such fragments would burn up as shooting stars because of the immense friction. Consequently, the major processes involved in meteorite impacts were studied first on the basis of

Meteorite impacts on the moon

the moon, before then looking for corresponding patterns on the earth. It was determined, for example, that practically all the craters on the moon are circular. This is attributable to the fact that an impact resembles an explosion - given the high speed with which the object hits and hence the craters are circular, irrespective of the angle of impact. Only with a very shallow angle of impact can elliptical craters form. Owing to the earth’s atmosphere, craters here can only be created by projectiles in excess of a certain size (> 30 m). Yet even from space, it is only possible to discern

a few of these craters, such as the 34-kilometer-wide West Clearwater crater in Canada, the Nördlinger Ries crater in Germany and the Kara crater in Pamir. Research into craters on earth has revealed that in the course of its history, it has been struck by numerous asteroids, yet the traces of the impacts have been carried away by erosion or covered over through sedimentation or the fragments burned up in the atmosphere if they were too small. Frequency statistics indicate that minor impacts are to be expected relatively frequently, but large impacts only very seldom. Explosions of objects in the atmosphere were observed, Meteorites

Rough Classification of Meteorites Iron meteorites

Chondrites

Stony meteorites

Stony-iron meteorites

Achondrites

Undifferentiated

Differentiated

Agglomeration of dust from the solar nebula

Melting, crystallization in the parent body

Age: 4.55 bn years (oldest bodies in the solar system)

Age: < 4.5 bn years (e.g. Martian meteorites 1 bn years)

Asteroids that can be seen falling to earth in the night sky are known as meteors (or shooting stars). Meteorites are the remnants of asteroids that can be found on earth in the form of pieces of rock. Up to 50,000 objects fall to earth every year. Depending on their composition, meteorites are divided into stony, stony-iron and iron meteorites. Accounting for 97% of all meteorites, stony meteorites are the most common. A distinction is made here between chondrites with a grainy structure, carbonaceous chondrites with admixtures of water and carbon, and achondrites with an iron core. The carbonaceous chondrites are considered to be primary rocks that reflect the very earliest phases of planet formation. The achondrites melted at a primitive stage, producing an iron core. Stony-iron meteorites are composed of a mixture of iron and crystallized metals. Iron meteorites can be differentiated according to their admixtures of other metals, e.g. nickel.

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Meteorite fragments found on earth

Impacts on the earth and diameter of the craters

<5 5 -20 20 -50 50 -100 > 100

Isotopes and Rare Earths Isotopes of an element are distinguished by the number of components in their nucleus. The protons determine the element, the neutrons determine the various modifications of the element, i.e. the isotopes. Isotopes play a significant role in documenting various processes. For example, the carbon isotope 14C is used to determine the age of tree rings and sediment layers. Cosmochemistry frequently makes use of the elements of rare earths, e.g. osmium and iridium. In meteorites, certain isotopes such as 188Os are enriched when compared with terrestrial rock, i.e. their presence is 10 -100 times higher.

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km diameter

for example, in 1908 in Tunguska, Siberia, 1930 in Curuca, Brazil, and 1935 in Rupununi, British Guyana.

Objective Criteria for Identifying an Impact Crater The effects of an impact on the earth depend on numerous factors: the mass, density, shape, solidity, size and speed of the projectile, the angle of impact and the impact site (land or water). Impacts by objects greater than one kilometer in diameter are classified as catastrophic events, although objects smaller than this can also cause considerable damage. Various criteria can be used to unambiguously identify a crater as an impact site. Some simple characteristics, such as a circular shape, central mountain peaks

in the middle or inner peripheral mountains, do not serve to distinguish impact craters from volcanic craters or collapsed structures. Noncircular impact craters are also found, where they have been deformed by tectonic forces or the impact occurred at a very shallow angle - circular craters result from impact angles of around 10°- 90°, while a glancing impact angle of less than 10° gives rise to elliptical craters. If the geological structure of the subsoil in the region does not permit the formation of craters (no tectonic forces at work, no volcanoes), this would indicate the presence of an impact crater. Various geophysical methods are used to investi-

gate these anomalies, e.g. measurements of the earth’s gravitational field or the earth’s magnetic field or the propagation pattern of artificially emitted seismic waves. Yet even after the anomalies have been identified, it cannot be certain whether they were caused by an impact. The next step is geological rock analysis. The composition of meteorites differs from that of the local rock. Often, however, meteorites vaporize in the air or on impact, leaving no consistent rock remains. Upon impact, the substance of the rock is also so greatly altered by the extremely high pressures and temperatures (metamorphosis) that only the existence of foreign minerals (e.g. diamond or coesite and stishovite, high-pressure modifications of quartz) can point to an impact. The presence of stishovite is to-

The 10 Largest Known Impact Craters Crater

Place/Region

Position

Diameter Age (km) (in million years)

Vredefort

South Africa

27:00 S 27:30 E

300

Chicxulub

Mexico, Yucatan

21:20 N 89:30 W

300

65

Sudbury

Canada, Ontario

46:36 N 81:11 W

250

1,850

Popigai

Russia

71:39 N 111:11 E

100

36

Manicougan

Canada, Quebec

51:23 N 68:42 W

100

214

Acraman

Australia

590

2,023

32:01 S 135:27 E

90

Chesapeake Bay Crater USA, Virginia

37:17 N 76:01 W

90

36

Puchezh-Katunki

56:58 N 43:43 E

80

167

Morokweng

South Africa, Kalahari 26:28 S 23:32 E

70

145

Kara

Russia

65

70

Russia

69:06 N 64:09 E

9

The Meteor Crater as seen from space. Due to its diameter of 32 kilometers, this crater can be clearly seen in the upper left half of the image.

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day considered to be a highly reliable indication of an impact, since this form of quartz cannot occur on the earth under natural conditions. The last step in proving the existence of an impact crater is to resort to geochemistry. The mixing ratios of rare elements in the rock are compared. Certain elements are found far more commonly in meteorites than they are on earth. If analysis of the crater rock points to a significantly high concentration of certain rare elements, it is very likely that an impact occurred. It is by no means unusual for the differences to be measured in factors of 100 to 1,000. Isotopes - i.e. in effect the same elements but with a different number of neutrons in the nucleus are used to improve accuracy. The isotope composition of the meteorites is entirely different to that of rocks in the vicinity of the crater. If the composition of the rock indicates that it came from a meteorite, the presence of an impact crater can definitively be determined.

Approximately 200 meteorite craters have been identified to date, the majority of them in the United States, Central Europe and Australia. Around two to five new craters are discovered every year. The smallest of them are just a few meters in diameter, the largest extend up to 300 kilometers. A theory to emerge in recent years suggests that large meteorites which hit the ocean can penetrate so deeply into the earth’s crust that they can cause a tear in the mantle. This allows fresh magma to flow upwards and can cause volcanoes on the earth’s surface. This could explain a number of so-called “hot spots,” i.e. volcanoes not located at the edge of plates. The earth’s crust melts at the edges of the plates in the subduction process and is carried to the earth’s surface due to its lower density. This then gives rise to familiar volcanoes such as those in the so-called Ring of Fire around the Pacific. In rare cases, however, volcanoes are found away from the edges of continental plates - something for which

Trend in the Discovery of Near-Earth Asteroids from 1980 to 2000 The number of asteroids identified has increased sharply, especially since 1998. Number 1,000 800 600 400 200 0 1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000 Year

All near-earth asteroids Large near-earth asteroids

Number of Asteroids Classified According to Their Diameter Number of asteroids 150 million/10 m

100,000,000 1,000,000

320,000/100 m 9,200/500 m

10,000

2,100/1km 400/2 km

100 1 10

100

1,000

10,000 Diameter in meters

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a cogent explanation has hitherto been lacking. According to the latest research, Hawaii - as one of these hot spots could therefore have been created by a meteorite impact.

What Happens upon Impact? Asteroids enter the earth’s atmosphere at a speed of 15-25 kilometers per second (54,000 -90,000 km/h), whereas comets can reach up to 70 kilometers per second (252,000 km/h) if they crash head-on into the earth. Depending on their mass and velocity, these bodies are then slowed to the normal speed of fall in the atmosphere (around 200 km/h - the speed with which a parachutist falls to earth). Many meteorites lose the bulk of their mass on entry into the earth’s atmosphere as they melt and vaporize. The atmosphere has the effect here of a wall, suddenly decelerating objects so sharply that many of them are torn apart in the air - they literally explode. Every year, the earth is struck 20 -30 times by fairly small objects which cause sizeable explosions in the atmosphere, as was the case, for example, in 1994 over the South Pacific (explosive force roughly a quarter that of the Hiroshima bomb) and in 1990 over Canada.

Yet the larger the asteroid, the less it is slowed and hence the more speed it retains. It becomes increasingly likely that it will only be destroyed on impact. The largest meteorite discovered on earth is made of iron and measures 3 x 3 meters. It was found in northern Namibia. Despite its considerable weight, it penetrated to a depth of just two meters. Meteorites composed of rock, on the other hand, break up more easily, which is why no sizeable fragments have been found. During the contact and compression phase, the projectile smashes into the earth’s surface. If there were no atmosphere, there would be no prior interaction between the projectile and the site of impact. Owing to the presence of the atmosphere, however, a cushion of air is compressed ahead of the object, and this then gives notice of the projectile’s arrival at supersonic speed. The very rapid deceleration gen-

The ejection phase commences with the explosive expansion of the rock at the point of impact owing to the high pressures and temperatures. A molten wave of pulverized and vaporized material spreads out from the point of impact and may travel a very considerable distance before it falls to the ground again. Displacement and ejection of the material create a bowl-shaped crater that is many times larger than the impact projectile. With large-impact craters, the material can rise up into the stratosphere or even ascend into the earth’s orbit, only to fall back to earth over several years. In the subsequent period, parts of the rim of the freshly formed crater cave in and some of the material hurled upwards also settles back into the crater, thereby filling it up. Some of the most well-known meteorite craters include the Meteor Crater in Arizona, the Bosumtwi Crater in West Africa and the Nördlinger Ries in Germany.

The Chicxulub Impact the End of the Dinosaurs

Experts are now fairly certain that 65 million years ago, an asteroid was the cause of the dinosaurs’ extinction.

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erates shock waves, which cause the material to suddenly melt and vaporize. The pressures occurring here are around a million times the pressure of the earth’s atmosphere.

As early as the 1970s, there was speculation about the Cretaceous-Tertiary boundary, the period when not only the dinosaurs but also more than half of the animal and plant species known at that time died out. Of the remaining species, too, many were drastically reduced in number. This transitional phase can be identified in many rock strata around the world as the characteristic layer of clay between the chalkstones of the Cretaceous and Tertiary periods (K/T bound-

ary). Here, too, an isotope anomaly was found between the chalkstone strata and the clay. Since this stratum had been found in many areas of the world - with isotope anomalies up to a factor of 200 - the theory of an asteroid impact arose in the 1980s. Given the worldwide presence of this stratum, the impact must have been extremely large. Subsequent investigations then also unearthed large quantities of soot in the rock strata - an indication of extensive forest fires. Evidence was accumulating of an impact of gigantic dimensions - yet where was the crater? At almost the same time, in the early 1980s, a major gravity anomaly was discovered during a search for oil under the Yucatan Peninsula in Mexico. For a long time no further investigations were conducted. Only in the early 1990s were drilling samples taken and all the indications of an impact crater confirmed, despite the fact that absolutely no hint of an impact could be detected on the surface. Over the past millions of years, the crater had been virtually entirely covered over by sediments. Now all that remained was to answer the questions: how old is this crater, and could this have been the notorious impact that led to the extinction of the dinosaurs? Investigations revealed that the crater had a diameter of 300 kilometers and is located partly below the Yucatan Peninsula and partly beneath the Gulf of Mexico. It was thus of adequate dimensions to produce worldwide effects. Only its age remained to be determined. Using two independent methods, the age of the impact was determined to be 65 million years - precisely the age of the mysterious Cretaceous-Tertiary boundary. Evidence had thus been furnished for a cosmic event with dramatic repercussions for fauna and flora.

Based on our insights today, this is what is believed to have occurred: An asteroid roughly 10 kilometers in diameter approached the earth at a speed of around 100,000 kilometers per hour and passed through the atmosphere in a matter of seconds. The object heated up and was briefly brighter and warmer than the sun. The projectile burrowed into the earth’s crust to a depth of approximately 40 kilometers, but the earth’s crust soaked up the impact like a glutinous liquid. What remained was a crater roughly 300 kilometers wide and several kilometers deep. The object vaporized instantly in a massive explosion. The vaporized rocks released millions of tons of dust, steam, carbon dioxide and sulfur dioxide, darkening the sky for several months and causing temperatures to drop rapidly.

Gravitational anomaly in Yucatan and the Gulf of Mexico. The crater structure can be clearly made out.

Earthquake waves of magnitude 12 on the Richter scale spread out from the impact site. The impact in shallow water produced tsunamis with waves reaching a height of 100 meters and more. Smoldering chunks of rock fell to the ground tens of thousands of kilometers away from the impact site, setting fire to forests. Once the waves had subsided, the worst was over. Still, the darkening of the stratosphere resulting from the immense quantities of dust caused temperatures to fall, and the food chain collapsed as photosynthesis was disrupted. The enormous quantities of carbon dioxide exacerbated the greenhouse effect in the atmosphere and, once the dust had settled, it became warmer for many hundreds, indeed thousands, of years. Ultimately around 75% of all animal and plant species, including the dinosaurs, died out. The plant and animal world was unable to adapt to such abrupt climate changes, and only a few species survived the catastrophe.

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Traces of the Tunguska explosion could still be discerned decades later.

Impact Probabilities

In recent years the number of near-earth objects discovered has increased sharply.

For planetary researchers, 1994 was an exceptional year. For the first time it was possible to predict and ultimately observe the impact of comet fragments on Jupiter. The skies are routinely scanned for near-earth objects, and in 1993 a bright string of pearls was discovered that was ultimately identified as the remains of the roughly four-kilometerlong, fragmented comet ShoemakerLevy 9. On the basis of the comet’s path, it was calculated that these fragments would impact Jupiter in 1994. When, in 1994, the pieces finally hit Jupiter, the results of the impact of the largest fragment, one to two kilometers in size, could be clearly seen in the form of a crater with a diameter of more than 10,000 kilometers. Further impacts followed with comet fragments measuring several hundred meters in diameter. It was thus proven that impacts can occur anywhere in the solar system - with at times dramatic effects. The catastrophes described above in Mexico and Siberia demonstrated that catastrophic meteorite impacts have also occurred on earth. The meteorite that caused the Tunguska event is calculated as having been 50 meters in diameter; the Chicxulub object had a diameter of 10 kilometers. And in recent decades, further asteroid explosions have been observed, one of them in 1990 at a height of 30 kilometers above the Pacific Ocean. This raises the question of just how likely meteorites of various sizes are to hit the earth. The following conclusions have been reached, based on astronomical observations and studies of known impacts:

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In statistical terms, a 50-meter asteroid impacts somewhere on earth approximately every 250 years (corresponds to the Tunguska explosion), a 200-meter asteroid roughly every 5,000 years, a one-kilometer-sized asteroid about every 100,000 years and a 10-kilometer-sized asteroid - as was the case with the Chicxulub event - approximately every 20-60 million years. Needless to say, this does not mean that after the impact of the Chicxulub asteroid, for example, it will be 50 million years until the next such asteroid comes along. (Since the impact occurred 65 million years ago, this would wrongly imply that an impact today is highly probable. This is not the case.) As with storms, the average waiting period is merely an arithmetic mean figure: it is absolutely possible for a once-ina-100-year event to occur three times in succession, followed by a gap of 300 years. In other words, an impact can occur at any time - an entirely realistic scenario in view of the large number of potentially hazardous asteroids and comets and the small number of objects identified to date in space. Most objects larger than one kilometer are now known, but not all of them. Few of the smaller objects (such as that which caused the Tunguska event) are known. Even fewer of the comets are known, since they have comparatively lengthy orbit durations. Rough estimates suggest that there are at least 200,000 bodies with a diameter of several hundred meters whose paths intersect with the earth’s orbit. It is not enough simply to identify them; considerable effort has to be expended on determining their orbits. If we were to discover 10 NEOs per month, assuming the use of 150 tel-

The So-Called K/T (Cretaceous-Tertiary) Boundary Layer The sediment layers of the Cretaceous and Tertiary periods can be seen at the top and bottom respectively. The dark layer of the transitional period can be clearly made out between them.

64.9

Sediment layer after the meteorite impact: the deposits contain microfossils from the Tertiary period.

escopes around the world, we would still have to search for around 20 years to find and track them all - without even calculating the orbits. It is clear, then, that we will have to live with a good deal of uncertainty as to when the next impact will come, and it is not unlikely that the next impact will catch us by surprise.

Hazards and Potential Damage Calculations made by U.S. scientists compared the probability of deaths from cosmic events with that from noncosmic events. The frequency of events and the scale of effect in each specific case play a role here. They found that the probability of being killed by an electric shock or in an aircraft accident is roughly the same as that of being affected by the impact of a 1.5-kilometer meteorite. Of course, aircraft accidents occur much more frequently, and we are therefore conscious of this risk in everyday life. An impact by a meteorite of these dimensions, on the other hand, occurs only every 200,000 years, although the mortality rate can be as high as one-quarter of the world’s population. Depending on their size, meteorites pose the following hazards: ■ Heat wave ■ Pressure wave ■ Impact - crater formation ■ Rain of small rocks and dust ■ Earthquakes (in the case of major impacts) ■ Tidal waves - tsunami (in the case of an impact at sea) ■ Climate change (with objects greater than one kilometer in size) The repercussions of an event depend upon whether the impact occurs at sea or on land. If an asteroid explodes on land in an inhabited region, the subse-

Layer containing dust and soot thrown up into the atmosphere by the meteorite impact.

Ejecta with tektites: material ejected on impact and deposited over the course of days and months.

65.0 Layer before the meteorite impact: the deposits contain microfossils from the age of the dinosaurs.

65.1

Age in million years

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Hazards Associated with Meteorites Heat and pressure wave

quent pressure and heat waves will claim a large number of lives. An impact at sea would not produce any direct injuries or damage, but it would trigger a tsunami that would reach coastal areas with meter-high tidal waves. With more than 70% of the planet’s surface covered by water, the probability of an impact at sea is relatively high. The consequences for the insurance industry, however, would depend on the size of the impacting object. This can be illustrated on the basis of four different sizes of object: ■ Type I: Asteroid with a diameter of 0 -30 meters Roughly 10,000 -50,000 meteorites per year ■ Type II: Asteroid 50 meters in diameter (e.g. Tunguska event) Probability of occurrence: approximately once in 250 years ■ Type III: Asteroid one kilometer in diameter Probability of occurrence: roughly once in 100,000 years ■ Type IV: Asteroid 10 kilometers in diameter (e.g. Chicxulub event) Probability of occurrence: roughly once in 50 million years The probabilities of occurrence refer to an impact somewhere on earth, i.e. not necessarily in an inhabited region. However, the chance of an asteroid coming down somewhere over water or in an uninhabited area is very high. Type I asteroids are very common. They fall from the sky as dust or small rock fragments. As recently as March 27 of this year, a meteorite broke up into several pieces over the U.S., and its frag-

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Explosion, rain of dust and small rocks

ments crashed into several houses in the form of chunks of rock the size of tennis balls. While these objects can cause significant damage to, or even the total destruction of, individual risks such as cars, buildings or industrial risks, they do not pose any appreciable accumulation risk. Nor are further hazards such as heat waves, earthquakes or tsunamis to be expected. Asteroids of Type II will most likely explode in the air. If this occurs over land, the heat wave will ignite fires in the immediate vicinity that can inflict direct damage on forests, buildings and infrastructure. The subsequent pressure wave may extinguish such fires - but the structures will now be entirely demolished buildings can explode and trees will be snapped like matches. Total destruction should be assumed in the area closest to the impact. Large cities such as Berlin or Boston would be very extensively destroyed if they were to be hit. A rain of small rocks and dust would cause considerable damage. At greater distances, little damage is to be expected. The loss potential would surpass that of a major earthquake in, say, San Francisco or Tokyo. There would be no direct damage if the asteroid exploded over the ocean, but the tsunami could cause considerable damage even at great distances. If such a meteorite were to hit the Pacific, the tsunami would reach a height of 10-15 meters and could penetrate several hundred meters inland. Pacific Rim cities located directly on the coast, such as Tokyo, Vancouver and Los Angeles, would suffer substantial damage, depending on their distance from the point of impact.

Tsunami

Larger asteroids of Type III will generally impact the earth’s surface. On land, a crater around 20 kilometers in diameter would be created. Major cities such as New York, Tokyo or Berlin would be completely destroyed. Very heavy damage would be incurred within a radius of 500 kilometers (corresponding to the size of a small U.S. state or a federal state in Germany). Forest fires would rage across an area the size of an entire continent. A regional climate change has a considerable impact on flora and fauna. In the event of an impact at sea, large masses of water would be hurled more than 10 kilometers into the air. The resulting tsunami would lose momentum very quickly, but even at a distance of 1,000 kilometers, wave amplitudes of several hundred meters would be reached. Cities like Los Angeles, Tokyo, Hong Kong or Miami would be totally destroyed, with just a few ruins of reinforced concrete left standing. Asteroids of Type IV have global consequences. On land - the impact crater would measure roughly 300 kilometers across - entire continents would be destroyed. The damage can scarcely be quantified, since falling chunks of molten rock would ignite fires on a worldwide scale, burning down buildings and forests. Earthquake waves measuring 12 on the Richter scale would be unleashed. Other global repercussions would follow due to forest fires and the associated release of aerosols (cooling - “cosmic winter”), the increased greenhouse effect caused by higher emissions of carbon dioxide, the release of sulfur dioxide and the related acid rain (risk of corrosion), the destruction of the ozone layer

Hurling of water to a high altitude and release of water steam due to the intense heat

Release of gases from the vaporization of rocks, e.g. carbon dioxide, sulfur dioxide, nitric oxides

(worsened effects of hard UV rays, increased risk of cancer), radioactive contamination following the destruction of atomic power plants and nuclear weapons stores and chemical contamination caused by chemical risks. The food supply for humans and animals would be under acute threat. It is doubtful whether flora and fauna could adapt to such a dramatic climate change. Certainly, the dinosaurs and many other species of animals and plants were unable to cope with such changes some 65 million years ago.

Insurance Considerations For the insurance industry, asteroids of Types I and II are important because of their high probability of occurrence, and Type II all the more so owing to the potential accumulation risk. It should be

Earthquake

reiterated that while the likelihood of a Type II asteroid impacting close to a major metropolitan center is extraordinarily low owing to the small area concerned relative to the total area of the earth’s surface, such an impact can nevertheless occur at any time. There are various hazards that may be of relevance to insurers in the event of cosmic impacts, since they are applicable to the vast majority of policies: rockfall, fire, explosion, earthquake and tsunami. The fire and explosion hazards are generally covered, while protection against the other hazards can only be obtained by taking out appropriate supplementary coverage. It is not always clear, however, whether meteorite impacts are included as a trigger. A fundamental distinction must be made between all-risks policies and policies with named perils. Under

Number of Objects and Their Mean Frequency Number

Return period in years 100,000,000

100,000,000 Chicxulub event 10,000,000

10,000,000

1,000,000

1,000,000

100,000

100,000 Global consequences

10,000

10,000

Meteor Crater 1,000

1,000 Tunguska event

100

100

10

10

1

1 0

100 Number Return period

1,000

10,000 Diameter in meters

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Simulation of a meteorite impact (Sandia National Laboratories, USA) The meteorite explodes in the stratosphere and leaves behind a vacuum channel.

The meteorite approaches the earth.

The fragments impact the earth. A crater forms. Pieces of rock and dust are hurled upwards into the atmosphere.

3 km

Effects of Meteorite Impacts According to Their Size Diameter

Effects

< 30 meters Object will not normally reach the earth’s surface. 75 meters Iron meteorites create craters up to a diameter of one kilometer; stony meteorites explode in the air, cause a heat and pressure wave as in the case of the Tunguska disaster, and can completely destroy a city. 200 meters Impact on land destroys a major city such as New York or Tokyo. 350 meters Impact on land destroys an area as large as a small country; impact in the ocean causes moderate tsunamis. 750 meters Impact on land destroys an area as large as a mediumsized country; impact in the ocean causes severe tsunamis that can devastate numerous coastal cities. 2,000 meters Impact on land hurls large masses of dust and water steam into the upper atmosphere, has global repercussions due to climate change, and destroys an area the size of a large country or U.S. state, e.g. France or California. 10,000 meters Global repercussions due to falling chunks of burning rock, forest fires on a worldwide scale; destroys an area the size of several countries, threatens the survival of all fauna and flora, including mankind.

all-risks policies, coverage initially extends to all risks except those that are explicitly excluded. Under named perils policies, coverage extends only to the specified perils, whereas all others are in principle excluded. Policies with named perils frequently only refer to the impact of manned flying objects as a covered risk - where this risk is mentioned at all. In this case, direct losses and damage caused by meteorite strikes (rockfall only) are excluded. On the other hand, the fire and explosion risks as a consequence of a meteorite impact are covered, since with these perils the cause is immaterial. The earthquake and tsunami risks are also covered if supplementary coverage was agreed for these perils. Here, too, the cause is irrelevant. However, individual policies may contain endorsements or amendments that can lead to coverage of meteorite strikes. The existence of coverage under all-risks policies must generally be assumed, since “falling/flying objects” and “meteorites” are not normally explicitly named. Even if damage caused by manned and unmanned flying objects

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Scenario for an impact over a large city. Even though the possibility of an explosion occurring right over a major city is very remote, the illustration is intended

San Francisco

to show the effect of a Tunguskasized impact (object 50 meters in diameter) on a major metropolitan center. The inner circle indicates the area of total destruction.

Paris

is excluded, meteorites may be covered since “unmanned flying objects” can depending on court practice - be interpreted as referring only to artificial, i.e. man-made objects. Here, too, damage caused by fire and explosion as a consequence of meteorite impacts is covered, since the cause is immaterial. The same is true of earthquakes and tsunamis unless such perils are explicitly excluded. One exception would be countries such as Spain where natural perils and meteorite impacts are covered by the state. Cosmic catastrophes constitute a real risk. At once in 250 years, the probability of a Type II impact occurring somewhere on the earth can no longer be ignored. Of course, it is highly likely that these objects will come down somewhere in an uninhabited area or in the ocean at a considerable distance from inhabited coastal regions. But things may work out very differently, since a meteorite strike can occur anywhere at any time.

The second circle shows the area with considerable damage due to the heat and pressure wave. The third circle shows the area with scattered damage.

10 km 30 km 100 km

Tokyo

ing elements for this risk, no accumulation control is carried out, and the policy wordings make no clear differentiation between hazards. Although it is extremely difficult to determine the precise frequency of impacts broken down by region and to estimate the potential losses, it is undoubtedly necessary as a first step to examine this aspect more closely in the policy wordings and, where appropriate, to clarify what is covered and what cannot in fact be covered. This issue thus offers a parallel to the events of September 11, when a loss potential emerged that had previously been inadequately assessed and controlled. Could this be another risk from the realms of the impossible or unimaginable?

What we are describing here, then, is a risk that is covered under numerous standard insurance policies but for which no adequate risk assessment is performed. The premium does not include any pric-

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© Kölnische Rückversicherungs-Gesellschaft AG, 2003

This information was compiled by GeneralCologne Re and is intended to provide background information to our clients, as well as to our professional staff. The information is time-sensitive and may need to be revised and updated periodically. It is not intended to be legal advice. You should consult with your own legal counsel before relying on it.