Impacts: The Impending Doom
Albert Mindel, Jr.
Astronomy 1002 Ref 371741

Table of Contents

Introduction………………………………………………………………………………………………………………….3
Brief History and Gene Shoemaker’s contribution

Analysis………………………………………………………………………………………………………………………..6
Destructive power of Comets & Asteroids
Results of an impact on Earth

Conclusion……………………………………………………………………………………………………………………8
Is enough being done to protect humanity?
Different methods and theories being explored

Appendix…………………………………………………………………………………………………………………….12
Photos of impact crates, and techniques to deflect incoming objects

Bibliography………………………………………………………………………………………………………………..15

Brief History Natural disasters such as hurricanes, tornados, earthquakes, and tsunamis wreak havoc on humans caught in their path, but the destruction in often centrally localized. On August 28, 2005, Hurricane Katrina unleashed her destructive force on the Southern Coast of the United States, affecting several States to included; Louisiana, Mississippi, and Alabama. The reported death toll was more than 1,800 people and destruction of property surpassed $81 billion dollars. On December 26, 2004, an earthquake below the Indian Ocean triggered a Tsunami which claimed the lives of approximately 230,000 people in eleven countries. Waves of 30 meters (100 feet) high crashed into coastal communities, making the 2004 tsunami one of the deadliest natural disasters in recorded history. However, there lurks an even greater threat, one which cannot be seen by the naked eye from the surface of our planet, but could possibly destroy all biological life as we know it. June 30, 1908 was a quite morning deep in the Siberia tundra, when suddenly an explosion occurred, that would become known as the Tunguska event. In an article written by Jerry Coffey and published on universetoday.com, he states; “The Tunguska event may have exploded above the surface of the earth, but it exploded with the force of 15 megatons of TNT.” One megaton is a unit of explosive force equal to one million metric tons. The explosion knocked over 80 million trees covering an area of 2,150 square km (1,336 square miles); luckily the event occurred over a sparsely populated area. The bombs used by the United States against Japan to end World War II were only a fraction (21 Kilotons = .021 megatons) as strong. There were no man made weapons in existence then capable unleashing this amount of energy, so what was responsible for this unexplained occurrence? Some scientists believe that an asteroid was responsible for the destruction at Tunguska, still very little is known about the events of June 30, 1908, partly because of its remote location, and partly because of the secretive government which rules Russia. The capability or likelihood that an asteroid or comet could ever impact earth has long been the source of debate among the scientific community. The modern day pioneer in asteroids and comet impacts on Earth was Eugene Merle Shoemaker, (1928-197) born in Los Angeles, California graduate from the California Institute of Technology in Pasadena at the age of 19. Shoemaker was able to accomplish this not only because of his intelligence, but because the United States government mandated that during the war, students attending universities would do so on a year round basis, in other words no summers vacations. One year later after writing a thesis on “Petrology of Precambrian Metaphoric Rocks” he earned his master’s degree. Landing a job with the United States Geological Survey (USGS) sparked Gene’s interest in the moon. Gene often dream of traveling to the moon, as he felt what better scientist than a geologist to examine its contents, believing that craters would open the door to his dreams of setting foot where no man had before. His studies would encompass the relative role of asteroid impacts and volcanic eruptions in forming lunar craters. A visit to Meteor Crater located in Arizona, ignited the idea that both it and the craters on the moon were caused by asteroid impacts. Still employed by the USGS, he was assigned to study the craters created by small nuclear explosions under the Yucca Flats in Nevada. The comparisons between craters created by nuclear explosions and the lunar craters created by asteroid strikes had begun. Gene became so enthralled in his quest that he actually earned a Ph. D in 1960, from Princeton after writing a thesis on Meteor Craters. 1960 is the same year Shoemaker along with his wife and mother went on a trip to Southern Germany with the purpose of visiting the Ries Basin, a fifteen mile wide depression which scientist claim was formed by volcanic activities. The primary reason for the visit was to find evidence to support Shoemaker’s theory that the Ries Basin was an impact crater not a depression. An examination of some of the shock formed rocks in the area, and within the structure of St. George Church confirmed that Ries Basin was definitely an impact crater. The church was built from local material, and these bricks were filled with glass formed by shocked and melted rocks, exactly like he observed at Meteor Crater and the studies he conducted on the crater created by nuclear explosions. Ries Basin was twenty times the size of Meteor Crater and was proof that large impacts had occurred on earth in the past.
In 1961 Shoemaker took a lead role in the USGS mission at Flagstaff, Arizona, regarding the topic of aster geology. He was instrumental in designing the vehicles which were to be used in the exploration of the moon’s surface, and the training of the astronauts in the basic of geology. His lifelong dream of making it to the moon ended in 1963 when he was diagnosed with Addison’s disease. However, the contributions that Gene Shoemaker made to our understanding of the forces that shaped the face of both the earth and the moon were profound. Like most ideas in science, the idea that impacts actually occurred on the earth had long been proposed. Working mostly alone, Shoemaker proved it to be true, and during this process he overturn the conventional geological wisdom, which denied that impacts occurred. On March 23, 1993, Gene along with his wife Carolyn and his associate David H. Levy discovered a comet in the vicinity of Jupiter, which would be christen Shoemaker-Levy 9. Later that year, at the annual American Astronomical Society’s Division of Planetary Sciences meeting, Paul W. Chodas and Donald K. Yeomans, report a 99% probability of major fragments from Shoemaker-Levy 9 impacting Jupiter around the third week of July 1994.
Analysis
There remained a large segment of scientist who believed that there would be nothing to see, they claimed that the atmosphere of Jupiter would significantly destroy the comet before impacting the surface. The atmosphere indeed broke the comet into 21 pieces; however it did not destroy them. These pieces rained destruction down on the surface of Jupiter for a week. Of the 21 pieces, the ones which created the most damage were the fragments labeled G, K, and L. Fragment G was the largest impact of all, with an estimated energy equivalent to 6,000,000 megatons of TNT (approximately 600 times the arsenal of the world). In an article titled Comets: How Big a Threat to Earth, written by John Roach for National Geographic News, he quotes Robert Jedicke, an asteroid expert at the University of Arizona in Tucson “A key difference is that long-period objects, like comets will impact earth with much greater speed than a short-period object.” Big chunks of rock with a little ice are called asteroids, or big chucks of ice with a little rock are called comets. The consequences of a comet or asteroid impact on the earth are comparable. Both would cause wide spread destruction and loss of human life. “Does size and density of an object really matter?”
“Consider this example; an asteroid 0.6 miles (1 kilometer) wide with a density of 187 pounds per cubic foot (3,000 kilograms per cubic meter) traveling at 12 miles per second (20 kilometers per second) would impact earth with a force approximately 15 times greater than the world’s total nuclear arsenal. A Comet of just half the size and one-third the mass traveling at 37 miles (60 kilometers) per second, could achieve an impact of similar force if it were to strike earth. Size matters, but so does density and speed.” (Roach, 2003) Sixty-five million years ago an asteroid or comet impacted Mexico's Yucatán Peninsula, and created what is known today as the Chicxulub Crater. It is the belief of the scientific community that this impact is responsible for a major biological catastrophe were more than fifty percent of the earth species including the dinosaur became extinct. Exactly how the impact caused the mass extinction is not known as scientist have several different theories regarding the event. Some scientist think sulfur released by the impact lead to global sulfuric clouds that blocked the sun and also fell to earth as acid rain, or that the red hot debris from the impact caused global wildfires. Other scientists believe that the impact threw large quantities of dust up into the atmosphere, which block the sun and restricted plant growth.
Without the sun, earth would essentially become frozen tundra, unable to support much of the biological life known to man today. The food chain would be destroyed, because as the plants die, the decrease food supply and oxygen levels would affect the herbivores first, followed by the carnivores, and on up the line. Species which could survive this desolate winter would have to burrow underground, or live in caves, consuming alternative food supplies such as seeds, roots, and decaying matter. Most large mammals and reptiles would perish.
The general belief in the scientific communities is that most comets and some asteroids have orbits which bring them close to earth only once every 200 years. Such bodies are known as long period objects. Long period objects impact earth at a rate of one every 32 million years, whereas the rate of a comparably size asteroid is more likely once every 500,000 years. The problem is that finding and tracking these objects can be like looking for a needle in a hay stack. Since the last significant impact occurred sixty-five million years ago, at the Chicxulub Cater in Mexico, Earth appears to be on borrowed time. The question each of us should be asking is; what are the governments of the world and the scientific communities doing to protect and preserve the human race from the next killer impact?
Conclusion
April 2008, an Asteroid Defense Research Center was established on the Campus of the University of Iowa with Professor Bong Wie, the Vance Coffman Endowed Faculty Chair, as the founding director. The purpose of this center is to bring researchers from every nation together to address the issue of asteroids striking Earth. Many of these researchers have been studying the problem since the 1990’s, but have been unable to reach a common theory. The need for preventative measures was re-enforced by the Tunguska Event of 1908. The devastation which a similar event would wreak if it were to occur over a populated area is to mind boggling to express. Some astronomers are working to safeguard the earth from potential impacts by comets or other near earth objects in orbit around the Sun. As near-earth objects are detected, astronomers perform calculations on their orbits to determine if or when they pose a threat to impact the earth. These astronomers hope that they can detect all near-earth objects decades before they potentially pose a threat of impact. Meanwhile other astronomers are busy trying to figure out how to re-route threatening objects, thus eliminating the pending doom. Any attempt on asteroid deflection relies heavily on earlier detection of the threat. It would take a couple of years to build a missile that could carry an explosive device powerful enough to alter the path of the asteroid, and provide enough time for the deflections effect to widen the orbit enough so it would miss Earth. Even though there are a few potentially hazardous objects (PHO), asteroids deflection is still an uncertainty. This is because none of the theories on asteroid deflection or defense have been used on a near earth object. Strategies fall into two basic categories; destruction and delay. Destruction concentrates on rendering the asteroid harmless by breaking it up and scattering the fragments so that they miss Earth or burn up when entering its atmosphere. This does not always solve the problem, as sufficient amounts of material hitting the Earth at high speeds can have devastating results, even if they are not collected together in a single body. Delay exploits the fact that both the Earth and the asteroid are in orbit. An impact occurs when two objects reach the same point in space at the same time. Since the Earth is 12,750 km in diameter and moves at approximately 30 km per second in its orbit, so it travels a distance of one planetary diameter every 425 seconds or slightly over seven minutes. Delaying or advancing the asteroids arrival by more than seven minutes can cause it to miss the Earth. This theory relies heavily on accurately forecasting the impact time of the asteroid in order to determine how to change its velocity. One of the most often proposed solutions in asteroid defense is to fire a nuclear missile at the incoming asteroid in order to vaporize it. The problem with this method is when the asteroid breaks up into several pieces. The comet Shoemaker-Levy demonstrated the destruction which several pieces of an asteroid or comet could rain down on a planet. Another proposed solution is detonated several smaller nuclear devices alongside the asteroid, far enough away as to not fracture the object. This method is a form of nuclear pulse propulsion which relies on time and accuracy, as several small nuclear explosions will be used to alter the trajectory of the asteroid over a period of time; early detection is a must to avoid an impact. The last form of violently altering the course of an object is to kinetically pact the asteroid in attempts to directly alter its momentum by sending a spacecraft to collide with it. Many researchers argue that this method would be more efficient than others. There are several major alternatives to explosive deflection; one is called Asteroid Gravitational Tractor. This method would move the asteroid slowly over time, through the use of tiny constant thrusts designed to deviate an object sufficiently from its predicted path as to avoid an impact. Another method is to focus solar energy on the surface of an asteroid or comet to create thrust from the resulting vaporization of material. Over the course of several months or years enough solar radiation can be directed onto the asteroid to deflect it. One of the most fascinating ideas involves the use of a solar sail. The idea is to attach a large enough sail to the object, which would use solar pressure to shift the orbit of the asteroid. None of the theories in asteroid and comet deflection or defense has ever been tested. It is inconceivable that man can conduct an experiment here on earth on an object as massive as a comet that is capable of moving at the speed which these cosmic rockets generate. Government must take an active role in funding experiments in asteroid defense if the human race is to survive. Earth could not survive an encounter with a comet similar to the 1994 Jupiter vs. Shoemaker –Levy 9; such an event would end all biological life on the planet. Time will either be our greatest ally or worst enemy. Man has the responsibility to maximize the benefits time gives, by attempting to carry out experiments on near earth objects, even if they pose no threat to our planet. This will be the only way we will establish a fail proof defense against these extremely dangerous missiles traveling throughout our solar system.

Appendix
The Barringer Meteor Crater located in Arizona was the subject of controversy, until scientist mainly Gene Shoemaker provided proof that large impacts occurred on Earth. The crater is 49,000 years old.

The opinion of the scientific community is the Chicxulub Crater (depicted in this three dimensional map), located on the Mexican Yucatan Peninsula, is the impact responsible for the extinction of the dinosaur. NASA scientists believe that the asteroid which created this crater was 10 to 20 kilometers (6 to 12 miles) in diameter. This crater is approximately 65 million years old.

This crater is located in Wolfe Creek, Australia; it is believed that this impact took place 300,000 years ago. Oxidized remains of meteoritic material; and some impact glass have been found at Wolfe Creek.

This picture shows the impact crater on Jupiter from (Shoemaker-Levy 9 Comet) fragment G. Travelling at a speed of 60 kilometer (37 miles) per second this fragment was the most powerful of the comet’s 21 impacts. The dark central spot is 2,500 kilometers (1,550 miles) in diameter; it is surrounded by a thin dark ring approximately 7,500 kilometers (4,661 miles) in diameter. The outermost dark ring’s inner edge has a diameter of 12,000 kilometers (7,460 miles) in diameter, about the size of the earth.

A picture showing a passive method asteroid deflection, however this form would require that the object was detected years in advance. Having an abundance of time is the only way for an intervention of this sort to work.

As with the previous photo of asteroid intervention, the solar sail would require a huge amount of time in order to change the trajectory of the asteroid or comet. Earth would not be able to survive the majority of the impacts Shoemaker-Levy 9 rain down on Jupiter, so time will be either our greatest ally or our worst enemy.

Bibliography
Baalke, R. (1996, March 1). Comet Shoemaker-Levy Collision with Jupiter JPL. Retrieved October 29, 2009, from Comet Shoemaker-Levy Collison with Jupiter: http://www.2jpl.nasa.gov/sl9
Baalke, R. (2005, August 22). Images of Chicxulub Crater, NASA. Retrieved November 1, 2009, from Images of Chicxulub Crater: http://neo.jpl/nasa.gov/images/yucatan.html
Bruton, D. (1996, February 1996). Post Impact Questions and Answers tamu.edu. Retrieved October 30, 2009, from Post Impact Questions and Answers: http://www.isc/tamu.edu/~astro/sl9/cometfaq2.html
Cohen, D. J. (Director). (2007). Cosmic Collisons [Motion Picture].
Levy, D. H. (1995). Impact Jupiter. New York: Plenum Press.
Mason, B. (2009, August 12). Wired Science, News for Your Neurons. Retrieved October 28, 2009, from Wired Science: http://www.wired.com/wiredscience/2009/08/neoreport
Weinreich, E. (Director). (2003). Asteroids Deadly Impacts [Motion Picture].
Peebles, C. (2000). Asteroids. Washington D.C.: Smithsonian Institution Press.
Roach, J. (2003, January 28). National Geographic News. Retrieved November 14, 2009, from National Geographic: http://www.news.nationalgeographic.com
Williams, David R. (2005, February 4). Comet Shoemaker-Levy Collison with Jupiter NSSDC Planetary. Retrieved October 29, 2009, from Comet Shoemaker-Levy : http://nssdc.gsfc.nasa.gov/planetary/comet.html