Introduction
Problem and its Background
More than a hundred asteroids of kilometer size, which cross the Earths orbit are catalogued, and this represents perhaps 5% of the total of these fragments. There is thus a certain risk of a collision of an object a few kilometers in size with our planet This could provoke a climatic upheaval and extinctions of species, as in the past Even a hundred meter fragment could do great damage, and objects of this size are certainty much more numerous still than those of kilometer size (Zanda 2001 75). Collisions play a capital role in the Solar System. Moon origin, tilt of Uranus poleaxe, planet ring formation, craterization, and the actual figure of the asteroid population are due to collisions. Unfortunately, models of collisions lay on laboratory experiments in which the involved targets and projectiles are small objects. It is then difficult to apply scale laws to predict mass, velocity or spin distributions of fragments resulting from a collision between astronomical bodies, Parameters such as the gravitational attraction between the different fragments are not taken into account in laboratory experiment due to the small size of the bodies. During the last decades, the important role played by the occurrence of catastrophic collisions between the planetary bodies of our solar system has been progressively evidenced (Benest and Froeschle 1998 3).
Scope and Limitations
Meteor, comets and asteroids are some of the major ground bases of astronomical phenomena and developments of technological field; hence, focused study of such condition is essential. The case study involves the subjects of collisions with the heavenly bodies linked with the condition of determining the trends of probable disaster events implicated by such astronomical changes. The study shall determine the possible implications of meteors, asteroids, and comet collision in the body of astronomy. The following shall be utilized in the overall study.
To be able to determine and elaborate the aspects concerned and their contributions to the phenomena of collision between Earth and the heavenly body concerned
To be able to relate the possible trends of astronomy brought by the phenomenon of heavenly bodies’ collision to the Earth surface as impregnated to various astronomical incidents
To be able to compare and link the significance, similarities and differences present in the two forms and trends of astronomical phenomena
Purpose of the Study
The value significance of this study provides awareness to the public especially in terms of what can these contributing factors impregnate to the conditions of meteor, comet, and asteroid collisions towards the Earth’s surface. Moreover, the study compares the significant relationships involved in the situation of technology and astronomical intervention, which employs various new trends of astronomical management as derived from different incidents.
Page Outline
The study utilizes the astronomical subject of Earth colliding with various heavenly bodies, such as meteors, asteroids and comets. The study involves the previous history and events of such collisions dated from 1800s and the latest 2002. Furthermore, the study utilizes this subject in order to implicate significance in the trends of astronomical technology to further enhance aspects of prevention for such cases that may occur. The following are the sections discussed throughout the study and the implications posed:
A. Introduction
This section of the study provides an introductory background of the entire course research. As for the section, it describes the problem discussed and the background of the study itself. Furthermore, it utilizes scopes and limitations in order to specify the actual scope of the entire research study.
B. Brief Background and History
The section of the study describes the incidents of collisions from the very past time of Stone Age up to the present. Moreover, it illustrates the conditions brought by such phenomena, which somehow caused environmental threats.
C. Evolution of Knowledge
The section of the study determines the effects of such incidents in the development and enhancements of astronomical measures for the prevention of future possible occurrences of collision. The section involves the latest updates and previous theoretical and conceptual changes that have been utilized by astronomers in order to enhance the knowledge in regards to such phenomenon.
Discussion
Brief Background and History
Meteors are small fragments of matter that approach the Earth as it moves in space. Usually we see meteors as bright streaks in the sky, sometimes called shooting stars,” which occur when they burn up due to friction with the atmosphere. Occasionally, large meteors are not completely burned up in the atmosphere and survive to strike the Earth. These are called meteorites, which usually fall into one of three categories: stony meteorites with composition similar to ordinary rock; stony iron meteorites which are a matrix of stone and iron; and iron meteorites, consisting largely of iron with some nickel alloyed with it (Dubeck, Moshier and Boss 2004 43).
Meteors very rarely impact the earth since most are vaporized fifty to seventy-five miles up. However, the larger source particles of very bright sporadic meteors that survive their encounter with the atmosphere and impact the earth are called meteorites. Material in space not associated with a comet prior to entering the earth’s atmosphere is referred to as a meteoroid. Meteoroids can be made up of various types of objects often material left over from the formation of the solar system. Other types of bodies that can strike the earth include comets and asteroids. Asteroids (the word means “starlike”) are usually about a kilometer across. They are larger masses of rock and metal that predominately orbit the sun between the orbits of Mars and Jupiter, but a few are in orbits that cross the inner planets (Reynold 2001 8). The stony meteorites often contain organic compounds such as hydrocarbons and amino acids. These biologically important compounds evidently formed in the hot gaseous cloud (called a gaseous nebula) from which the solar system is believed to have formed. It is believed that meteorites (and their larger “cousins,” asteroids) are leftover “building materials” from which the inner solar system was fabricated five billion years ago (Dubeck, Moshier and Boss 2004 43). After the initial discovery of multiple asteroids in the space between Mars and Jupiter, it was theorized that a single planet once orbited there. According to the theory, the planet broke up, most likely due to the gravitational pull of its gigantic neighbor, Jupiter. Today’s astronomers believe that the asteroid belt is simply made up of material left over from the formation of the solar system. Astronomers also theorize that there were initially about seventy smaller bodies that broke into the thousands and thousands of asteroids that now form the belt.
Any planetary system is rife with cosmic debris: asteroids and comets, the residue left over from planetary formation. Great quantities of this material will eventually strike all members of a planetary system, and the energy released can spell planetary disaster. Such disasters are now known to have caused mass extinctions on Earth. In 1980, Luis and Walter Alvarez, Frank Asaro, and Helen Michel from the University of California at Berkeley proposed that one of the greatest of all mass extinctions, the 65-million- year-old event that killed off the dinosaurs and many other species living near the end of the Mesozoic Era, was caused by the impact of a large meteor or comet striking Earth. As evidence for this view mounted, most scientists realized that collision with a meteor or comet could cause a biotic crisis on any planet and that it has done so at least once (and probably other times as well) during Earth’s past (Ward and Brownlee 2004 164). The first asteroid discovered was Ceres, observed in 1801 by the Sicilian monk Giuseppe Piazzi, who believed it to be a planet orbiting between Mars and Jupiter. Astronomers had long theorized that a planet should be found at that distance because of a theory known as Bode’s law However, Ceres was small compared to the other planets (a little over five hundred miles in diameter). Eighteen years later another object was discovered in approximately the same orbit as Ceres. A number of additional objects were discovered in the following years, but none are larger than Ceres and only three of the asteroids are more than 250 miles in diameter (Reynold 2001 8).
Earth has had more recent collisions with large meteorites and/or comets. On June 30, 1908, a tremendous explosion occurred in a forested region near the Tunguska River in Siberia. The sight of a great ball of flame leaping from the forest was followed by an explosion powerful enough to level trees in an area of about 800 square miles. One estimate of the force of the explosion was that it was equivalent to 10—20 megatons of TNT exploding. No impact crater was located and thus the most probable cause of the explosion was a collision with a comet, which does not have a solid rock core (Dubeck, Moshier and Boss 2004 44). One of the by-products of a large meteor collision with the earth is the formation of line diamond crystals due to the explosion. The presence of hoe diamond crystals in a layer 65 million years old helped to formulate the theory that a large meteor impact was responsible for the extinction of the dinosaurs. One of die distinctive aspects of diamond created by explosion is that cubic as well as hexagonal (lonsdaleite) crystals are formed. An explosion is capable of creating millions of atmospheres of pressure in microseconds (Lee 2006 668). Scientists have speculated that the dinosaurs may have become extinct because of a collision with an asteroid or comet.
Many variables affect the degree of lethality resulting from a collision, such as the meteors size, composition, angle of impact, and velocity and the nature of the impact target area. In the case of the Cretaceous event (also known as the KIT impact), for instance, the target rock was rich in sulfur, which exacerbated the impacts environmental effects. (The sulfur reacted with air and water to produce a highly toxic acid rain that lasted many months after the impact event itself.) Moreover, not only the geology of the impact site, but also its geography, may play an important part. An impact in (Ward and Brownlee 2004 165) a low-latitude site will have entirely different consequences from a similar body hitting a high-latitude site at a similar angle and speed, because the distribution of lethality across the globe may be produced by atmospheric circulation patterns. An impact in a highly diverse world of ecological specialists—anima1s and plants with little tolerance for environmental change—might produce more extinction than the same event in a low-diversity world and an impact in the greenhouse world might have lowered the greenhouse content as of today (Ward and Brownlee 2004 166).
A comet or an asteroid has no problem penetrating the Earth atmosphere. However, the collision of a comet or an asteroid with the Earth could have devastating consequences for the environment and human civilization. Although events of this kind are extremely rare, they cannot be completely excluded as was shown by the collision between a comet and the planet Jupiter in 1994. As a consequence, Russian scientists suggested using the International Space Station as an outpost to search for objects in space that have a potential collision course with the Earth. Such a “warning system” would probably provide enough lead Lime to take suitable measures to protect the Earth from a global natural disaster. A large number of asteroids exist in our solar system. Some of them pass relatively close to Earth. However, the orbits of most of them lie between those of Mars and Jupiter. There are at least 100,000 asteroids that are a half-mile or more in diameter. The largest, Ceres, is over 600 miles in diameter. The asteroids that are of most concern to us are those whose orbits arc close to that of Earth. Near Earth Asteroids (NEAs) are asteroids whose orbits bring them within 121 million miles of the Sun. It is believed that NEAs are fragments jarred from the main asteroid belt by either asteroid collision or by the gravitational force (Dubeck, Moshier and Boss 2004 44). We have crater evidence that at least 200 large meteors have struck Earth. It is estimated that at least one large collision occurs each 10,000 years. For example, near Winslow, Arizona, the Baringer meteorite crater is located. It is nearly 500 ft deep and 4,000 ft wide, it was created by a meteorite weighing at least 30,000 tons, which struck Earth about 24,000 years ago. The collision must have devastated all plant and animal life in a large region around the crater (Dubeck, Moshier and Boss 2004 44). In April 2002, scientists announced that a 1.3-km-diameter asteroid, 1950DA, had a 1 in 300 chance of impacting the Earth. Its orbit was predicted using radar to measure its position and velocity more accurately than could be achieved by optical telescopes. Although, 1 in 300 odds may seem small, one expert said that it was the highest odds ever assigned by scientists to an object in space. The projected impact location is the North Atlantic off the US coast, similar to the collision depicted in Deep Impact. The good news is that the impact, if it occurs, will not happen until March 16, 2880. Thus, we have more than sufficient time to stop it (Dubeck, Moshier and Boss 2004 44).
Evolution of Knowledge
One theory suggests that every 26 million years or so a rain of comets that lasts for hundreds or thousands of centuries bombards the Earth. The impact of some of the larger asteroids or comets spews enough dust into the atmosphere so that it blocks the Sun’s rays from reaching the Earth for months or years and most of the plant and animal species on Earth perish. According to this theory the last extinction occurred about 11 million years ago so that the next calamity should not occur for another 15 million years. Scientists are searching the skies for evidence of a possible “dark star,” which they have named “Nemesis.” They suggest that Nemesis may circle our solar system every 26 million years. When it approaches our solar system, Nemesis passes through the region of space beyond the orbit of Pluto, which contains vast numbers of comets. Its passage would disrupt the comets’ orbits and send a shower of them toward the Sun. Some of these comets would then collide with the Earth (Dubeck, Moshier and Boss 2004 44). A collision or close encounter between Earth and the comet is avoided because the comet is not as the crossing point when the Earth is there. Some suspected sources of known meteoroid streams are the Comets C/1861 GI, 1P/Halley, 109P/Swift-Tuttle, 21/PGiacobini-Zinner, 2P/Encke, 55P/Tempel-Tuttle, 3D/Biela, and 8P/Tuttle (Denecke and Carr 2006 174).
Some investigators thought that a general synthetic model linking most or all mass extinctions to impact would emerge. This was the thinking behind the “Nemesis” hypothesis of astronomer Rich Muller from Berkeley, and it underlies the work of David Raup and Jack Sepkoski of the University of Chicago, who hypothesized in 1984 that mass extinctions show a 26-million- year periodicity (. Since then, elevated levels of iridium (the platinum-group element used by the Alvarez team as a sign of impact) have been found from 11 different time intervals in the geological record. Yet most of these are at such low concentration that they are nor indicative of larger impacts. The evidence date suggests that only the major mass extinction at the end of the Triassic and that at the end of the Cretaceous Period were brought about by the effects of impact (Ward and Brownlee 2004 166). Astronomers have classified asteroids based on their orbits. One group, the Apollo objects, are asteroids that have earth- crossing orbits. The gravitational pull of Jupiter affects the orbits of these asteroids, making them quite dangerous as their orbits shift. Close-up exploration of asteroids had to wait until recently. On its way to the planet Jupiter, the spacecraft Galileo made two all-important flybys of the asteroids Ida and Gaspra. Images sent back by Galileo revealed irregular-shaped bodies that had been battered by impacts. In 1996, the United States launched a spacecraft specifically to orbit and study an asteroid. The Near Earth Asteroid Rendezvous, or NEAR, arrived at the asteroid Eros in February 2000. Data from NEAR indicates that Eros, a twenty-one-mile-long asteroid, is an irregular-shaped solid body, showing many impact features and n moons or debris surrounding the asteroid. Eros, apparently a very old asteroid, passes close to, but never crosses the earth’s orbit were once members of the main asteroid belt but was ejected by Jupiter. There is also a possibility that some NEAs are dead comets. NEAs are considered dangerous to the earth if they pass within three million miles. (Reynold 2001 10).
The presence of numerous impact craters on every stony planet or moon of the solar system is stark evidence of the frequency of these events, at least early in the history of our solar system. It is probable that impact is a hazard in most, or perhaps all, other stellar systems as well. Impacts are probably the most frequent and important of all planetary catastrophes. They could completely reset the course of the biological history of a planet by removing previously dominant groups of organisms, thus opening the way for entirely new groups or for the rise to dominance of previously minor groups (Dubeck, Moshier and Boss 2004 46).
The larger the asteroid or comet, the less likely that an impact will occur but the more damaging the impact would be. One study suggested that impactors with a diameter of less than 10 m would likely not cause any damage because most of them will burn up or break up in the upper atmosphere. For impactors with a diameter of 75 m, iron asteroids will make craters like Meteor Crater; stony asteroids will produce airbursts such as that at Tunguska and a land impact would destroy a city because the energy released would be in the range of 10—100 megatons of TNT. A 350-rn-diameter impactor would destroy an area the size of a small state. If it struck an ocean, it would produce a mild tsunami. It would release energy in the range of 1,000—10,000 megatons of TNT. An impactor 1,700 m in diameter (about I mile) would destroy an area the size of France and raise dust with global consequences. Its impact energy would be 100,000—1,000,000 megatons. The frequency of such an impactor hitting is about once every million years. The death total could be 1.5 billion people! Even larger impactors could wipe out all human life on Earth (Dubeck, Moshier and Boss 2004 46).
The most likely location for an impactor is in the oceans, which cover most of the Earth’s surface. For example, an impact of a stony asteroid more than 400 m in diameter anywhere in the Atlantic Ocean could devastate coasts on both sides of the Atlantic with tsunamis that would reach 60 m at the shores. An asteroid with energy of 40 million Hiroshima-style bombs hitting in the center of the Atlantic would produce a gigantic tsunami at the shore that might reach a height of 100 m. Thus, the risk to a low-lying coastal area from a tsunami generated by asteroids is significantly greater than the risk from a direct impact by such objects. However, an ocean hit would result in less dust being thrown into the air than a land hit. The overall risk that an object of diameter 100 m (the approximate size of the Tunguska impactor) or so will strike the Earth is that such an impact will occur once each century. One researcher estimated that the odds that an “extinction-level” object 2—5 km in diameter will strike the Earth this century is about I in 1000 to 1 in 10,000 (Dubeck, Moshier and Boss 2004 46).
In order to deflect an object on a collision with the Earth, we must first find it. At present, several organizations are searching the skies for NEOs. Deflection technologies also need to be developed. They will likely need to include nuclear devices, which raise security issues. In addition to using nuclear weapons, other ideas include attaching rockets to the NEO’s surface, which fire for a sufficient period of time to change its orbit away from a collision with the Earth. Also, one could place a mass driver on the NEO’s surface to accelerate part of the NEO into space, while the reaction would move the NEC) into a different orbit. Finally, one could attach thin solar sails several kilometers in size to the surface of the NEO and let the solar wind change its orbit (Dubeck, Moshier and Boss 2004 46).
Scientists invented the Torino Scale to categorize the Earth’s impact hazard associated with newly discovered asteroids and comets. It is intended to serve as a communication tool for astronomers and the public to assess the seriousness of predictions of possible impacts by asteroids and comets. An object is assigned a value of 0 to 10 based on its collision probability and its kinetic energy. The value “0” means either that the object has little chance of striking the Earth or that it is so small that it would not do damage if it did hit the Earth. The value “3” is a dose encounter with a 1% chance or greater of a collision that would do localized destruction. The value “7” is a close encounter with an extremely significant threat of a collision capable of causing a global catastrophe. Lastly, the value “10” is a certain collision capable of causing a global climactic catastrophe. The crash of Comet Shoemaker—Levy into Jupiter demonstrated the destructiveness of an impacting comet. The comet had broken up into more than 20 fragments, which impacted separately. One of the impacts affected an area as large as the entire Earth! There is little doubt that had the Shoemaker—Levy fragments struck the Earth, the human race would have been annihilated (Dubeck, Moshier and Boss 2004 47).
Conclusion
The phenomenon involving the collision of asteroids, meteors and comets have greatly initiated even before the Mesozoic era of the dinosaurs, which is one of the proposed theory for their extinctions. Apparently, the collision caused severe environmental changes, and climatic damage that greatly endangered the ecological balance present. The significance of studying such subject in astronomy is the fact that technology can predict the probable trends, projections, and damages that may have resulted in such collision. Moreover, determining such angle of causation provides possible cautionary measures for possible disastrous implications that might be brought by the incident. Such knowledge have greatly inculcated vast structural modifications in the technological aspect of astronomy, and provided enhancements in astronomy.
Works Cited
Benest, Daniel, and Claud Froeschlé. Impacts on Earth. Springer, 1998.
Denecke, E J., and W H. Carr. Let’s Review: Earth Science. Barron’s Educational Press, 2006.
Dubeck, L W., S E. Moshier, and J E. Boss. Fantastic Voyages: Learning Science Through Science Fiction Film. Springer, 2004.
Lee, S. Encyclopedia of Chemical Processing. CRC Press, 2006.
Reynolds, M D. Falling Stars: A Guide to Meteors and Meteorites. Stackpole Books, 2001.
Ward, Peter, and Donald Brownlee. Rare Earth: Why Complex Life Is Uncommon in the Universe. Springer, 2003.
Zanda, B. Meteorites: Their Impact on Science and History. Cambridge University Press, 2001.
Zichichi, Antonio, and Richard C. Ragaini. International Seminar on Nuclear War and Planetary Emergencies: 25th Sessions. World Scientific, 2001.
