 | Main Belt: located between Mars and Jupiter roughly 2 - 4 AU from the Sun; further divided into subgroups: Hungarias, Floras, Phocaea, Koronis, Eos, Themis, Cybeles and Hildas (which are named after the main asteroid in the group). |
Kailyn Derck
November 20, 2003
Asteroids: Impact
On January 1, 1801, Giuseppe Piazzi discovered what he believed was a small planet. But after careful evaluation and study, he realized it was not a small planet at all, but an orbital mass. "Asteroids are rocky and metallic objects that orbit the Sun but are too small to be considered planets" (Hamilton). He called this orbital mass Ceres after the Sicilian goddess of grain and thus began the exploration and discovery of asteroids (Arnett).
Asteroids have since been studied by astrologists. After Ceres and Piazzi’s research, the bodies of Pallas, Vesta, and Juno were discovered (Arnett). At the end of the 19th Century several hundreds of asteroids were discovered, named, and recorded. Today there are thousands of asteroids named and positioned with an orbital direction. Thousands more are being discovered every year and scientists believe there are hundreds of thousands waiting to be discovered or too small to be seen from the earth (Arnett).
Piazzi’s asteroid, Ceres, is the largest asteroid known and recorded at this time. It is about 1,000 kilometers or 600 miles across and, if all the known asteroid masses were to be combined, it would hold 25 percent of that mass (Lutgens, Tarbuck 595). There are only 26 known asteroids larger than 200 kilometers and scientists estimate they know at least 99 percent of the asteroids larger than 100 kilometers (Arnett). The next largest asteroids after Ceres are Pallas, Vesta, and Hygiea. They range in size from 400 to 525 kilometers in diameter (Arnett).
Asteroids primarily lie between Mars and Jupiter (Lutgens, Tarbuck 595). This is called the Asteroid Belt because of the abundance of asteroids in this area. Bill Arnett said the following:
| Main Belt: located between Mars and Jupiter roughly 2 - 4 AU from the Sun; further divided into subgroups: Hungarias, Floras, Phocaea, Koronis, Eos, Themis, Cybeles and Hildas (which are named after the main asteroid in the group). |
| Near-Earth Asteroids (NEAs): ones that closely approach the Earth
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| Trojans: located near Jupiter's Lagrange points (60 degrees ahead and behind Jupiter in its orbit). Several hundred such asteroids are now known; it is estimated that there may be a thousand or more altogether. Curiously, there are many more in the leading Lagrange point (L4) than in the trailing one (L5). (There may also be a few small asteroids in the Lagrange points of Venus and Earth (see Earth's Second Moon) that are also sometimes known as Trojans; 5261 Eureka is a "Mars Trojan".) |
Between major concentrations of asteroids, such as the Asteroid Belt, there are empty regions. These empty regions are called "Kirkwood gaps" (Arnett). Objects in this region often have an orbit only a fraction of that of Jupiter. They are also often accelerated by Jupiter and may therefore be pushed into a different orbit.
On May 9, 2003, the Hyabusa mission was launched in hopes of reaching, landing on, and collecting data from an asteroid. The asteroid in target is Itokawa. The space craft is meant to be in close orbit near the asteroid and make contact in June 2005. From here it will follow the orbital patterns of the asteroid for three months as the asteroid moves toward the sun. It will then touch down and take data samples at three locations on the surface of the asteroid. Scientists hope to collect and test this information to better understand asteroids. Several satellites are already in orbit around asteroids and are relaying information to scientists. This is very helpful information and it guides them to defining and identifying asteroid behavior, make-up, over-all purpose, and where they come from.
Several asteroids have hit the earth. According to NASA, there is no threat of an immediate asteroid impact in the near future. A very large asteroid hits the earth every 100 million to 1 billion years and a large asteroid hits the earth less than 100 million years. Asteroid’s impacts are obvious throughout the Earth at various impact sites and especially on the moon. The Earth has fewer craters than the Swiss-cheese-like moon because of erosion and weathering. One of the best preserved craters on the earth is in Winslow, Arizona, at the Barringer Meteor Crater (Hamilton). It is .737 miles in diameter and 49,000 years old (Hamilton).
About 60 million years ago an asteroid hit the Earth in the Gulf of Mexico off the Yucatan Peninsula. This asteroid is said to have caused a mass extinction of the dinosaurs. Because of the estimated size and impact of this asteroid, 70 percent of life perished. It is possible the sky was scorched with dust and debris for years following the impact, thus causing vegetation to die. The entire eco-system and food chain at the time collapsed.
Such a catastrophic event is not likely to occur for another 100 million years or so. The crater caused by the asteroid is submerged under water.
Asteroids are still being discovered and studied. There is much to be learned about their make-up and history. This is just the beginning!
Works Cited
Arnett, Bill. "Asteroids." 19 May 19 2003.<http://seds.lpl.arizona.edu>.
Hamilton, Calvin J. "Views of the Solar System." 2003. <http://solarviews.com>.
"Asteroids." 2002. <http://www.solarviews.com>.
Sawyer, Donald M. "Hyabusa." 2 Sept. 2003. <http://nssdc.gsfc.nasa.gov>.
