Threats of Near Earth Objects
There are many objects floating within Earths orbit. These objects vary from small asteroids of 10-100m in diameter to 1km wide asteroids. Despite the high number of these objects within or near earth’s orbit, the probability of these objects actually entering earth’s atmosphere and making an impact is extremely low.
The media and the general public focus the majority of their attention on the infamous 10km+ asteroids which is evident through two widely acknowledge films Armageddon and Deep Impact, both featuring asteroids large enough to wipe out the human race. Events such as these are feared by many, assuming they could happen sometime in the near future. However these assumptions are misconceived. It is estimated that asteroids as large as 10km only come into contact with earth’s atmosphere every 50-100 million years. In fact an asteroid this large has not hit the Earth since the time of the dinosaurs 60 million years ago, long before the beginning of the human race.
Smaller asteroids however have contrary statistics. There are approximately 2000, 1km sized asteroids that have recently come close to, or within earth’s orbit. Due to their size, these asteroids are possible to detect with our telescopes. We can follow their gravitationally destined paths and determine whether or not their course will lead them to collide with earth. Thus far scientists have ascertained that these 1km-sized asteroids will not come in to contact with Earth’s atmosphere for at least the next 1000 years.
The threat most scientists are concerned about are the 100m or smaller asteroids. These asteroids have a lessened impact but the frequency of them coming into contact with our atmosphere is much higher. At present there are over 300 000 of these smaller asteroids within or near earths orbit. Scientists estimate that these asteroids hit earth’s surface at the rate of 1 every 100 years. However their estimations are extremely vague. Due to the small size of these particular NEO’s, they are significantly harder to detect. Our current telescopes only begin to see them as they come closer to earth, at which point little can be done to minimise their impacts.
Impacts of Near Earth Objects
The impact an asteroid or comet has on our planet depends on various factors; these include size, speed, composition of the object and where the object hits, (i.e. land, ocean or air burst). The worst possible effects would result from an asteroid impacting on the ocean. An asteroid hitting land would cause great damage, but it would only be localised damage. If an asteroid hit an ocean a tsunami may result and would cause devastating affects on many coastal cities. Large populations tend to congregate around coastal areas, and the huge water wall, along with the floating debris would cause large loss of lives and complete destruction to nearby coastal cities. Unfortunately, the possibility of an asteroid hitting ocean is extremely high, as water covers over 70% of earth’s surface.
The devastation caused by the impact of an asteroid very much depends on the speed of the object. The typical speed of asteroids when contacting with earths atmosphere ranges from 10-20km/s, depending on the angle at which they are descending. Fortunately earth’s atmosphere provides protection against a majority of the smaller asteroids. The severe pressure of the atmosphere causes the asteroids to break up and then due to the friction caused by the rapidly moving asteroid the remaining fragments burn up before impacting with earth’s surface.
Asteroids are characterized into three main sizes, and each size has a varying impact:
On the rare occasion that an asteroid 10km in diameter were to come into contact with earth’s surface, the impacts would be completely devastating. The asteroid would hit earth with a force of approximately 100 million megatons of TNT. It would most likely wipe out all life on earth not only from the effects of the initial impact but also from resulting issues. A large dust cloud would appear between earth’s surface and atmosphere, blocking the sun and causing a long lasting ice age. Many of the surviving animals could not withstand such a drastic change in climate and temperature patterns and would eventually become extinct.
The implications of a 1km wide asteroid would be almost as devastating. All life within a close proximity to the impact site would be immediately wiped out. Following the impact, a dust cloud would again form causing a “nuclear winter”. Climatological wind patterns would be disrupted, causing major issues with food growing and agricultural regions. The basic necessities of life would be put on strain, and governments and societies would begin to falter under the financial and resource attainment pressures.
Due to the protection provided by earth’s atmosphere a smaller astroid would have to be 40m in diameter for an iron asteroid or 200 m in diameter for a rocky asteroid to even make contact with earths surface. These smaller asteroids (again depending on their size), can still cause major damage to wherever they hit, however longer lasting impacts such as an ice age will not occur. The damage from these asteroids is destructive and immediate but not as long lasting.
History of NEO’s
– One of the most significant events in history, resulting from the collision of an NEO was before the beginning of the human race. It was the event most scientists believe caused the extinction of 90% of living beings, it is this asteroid that is said to have wiped out the dinosaurs. The asteroid that caused this immense destruction is thought to be one of the rare 10km wide asteroids. Scientist estimate that this asteroid hit over 65 million years ago in the Yucatan Peninsula in Central America.
– Another infamous asteroid impact was on June 20, 1908 in Tunguska, Siberia. An asteroid estimated to be from 30-60km in diameter and between 10,000- 100,000 tons in mass flew through earth’s atmosphere and exploded only 5 km above the earth’s surface. This explosion is said to have been 1,000 times greater than that of the nuclear bombs used in World War II. Fortunately, this all occurred in a very remote place over a forest, resulting in no human casualties. The explosion however, did result in the knocking down of over 80 million trees and the death of over 1,500 reindeer. Due to the angle at which the asteroid was descending (on the diagonal) many people did notice a fiery object soaring through the sky. There have also been reports of people feeling the ground shake and objects sliding off shelves. Scientists were unable to predict this incoming asteroid due to is small size and the lack of able technology at the time. It was not until 19 years later after the Russian Revolution and World War I, in 1927, when scientists actually ventured to the site to study the remains, did they discover what in truth happened. The scientists deduced that when the asteroid exploded in the sky most of the rock vaporised into dust and no large chucks actually hit the earth. The Tunguska event is the largest impact event to have occurred in earth’s recent history. Many events of the same sort could have easily have occurred over oceans in the past, but have gone unnoticed due to the only recent invention of the satellite monitoring in the 60’s.
– On March 23, 1989 an asteroid passed within earths orbit only 400,000 km away. This asteroid is presumed to be larger than an aircraft carrier with kinetic energy over 50,000 times as powerful as the Hiroshima nuclear bomb explosion. This asteroid was only detected six hours after it passed through our orbit, and would it have collided, millions of people would have died instantaneously. Although it was a very fortunate near miss, it is because of this asteroid (named 1989FC) that the threat of asteroids and comets was finally brought into the political arena.
The near miss event in 1989 prompted the research into the threats and impacts associated with NEO’s. The AIAA (The American Institute of Aeronautics and Astronautics), decided to publish an article entiltied “Dealing with the Threat of an Asteroid Striking the Earth” .
The above link is to a site containing the AIAA position paper “Dealing with the Threat of an Asteroid Striking the Earth” .
This article spurred interest in the topic from the US House of Representatives’ Committee on Science, Space and Technology. The Committee then proceeded to make a statement, acknowledging its agreement of the importance of asteroids and their threat to our planet. After this statement, NASA conduct workshops focused on the detection of asteroids and the interception of asteroids, both with the main idea of minimising or preventing damage to earth. Subsequent to the US governments commitment to the asteroid issue, many new technologies have been developed. At present the main methods in place for the detection of asteroids are:
– Telescopes (large asteroids)
– Satellite Observations (after a hit)
– Ground Observations (after a hit)
– Acoustic recording of explosions in the atmosphere (after a hit)
As evident above, it is clear that the technology avaliable at the present time is not advanced enough to detect NEO’s similar to the of the Tunguska asteroid . These smaller asteroids are only visible once in our atmosphere burning through the sky. By this time, not much can be done to prevent major destruction. Most of the equipment mentioned above is used after an asteroid explosion or after a near miss to characterise that particular object, which obviously is not extremely helpful if wanting prior knowledge of an incoming asteroid.
Some would say the threat of asteroids and their disastrous impacts is not given enough attention by the people that can make a difference. Although the US government has acknowledge that this issue does need addressing, they, along with the governments of many other countries are reluctant to donate any of their time or money into this issue. The two main priorities of this issue are; ensuring we have the technology needed to detect and define NEO’s, and creating systems that are able to destroy or deflect asteroids predicted to hit earth. Although millions of dollars will be spent refining and producing new technology, this cost would be nothing compared to the cost of even a small asteroid impacting earth. As all countries and cities are under the threat of these dangerous asteroids, it is the duty of all able governments to aid in the development of an efficient system able to detect and deflect these destructive NEO’s.