Threat from Above Essay

Submitted By ncelli
Words: 1240
Pages: 5

Comets: A comet is a relatively small solar system body that orbits the Sun. When close enough to the Sun they display a visible coma (a fuzzy outline or atmosphere due to solar radiation) and sometimes a tail. Comet nuclei are known to range from about 100 meters to more than 40 kilometers across. They are composed of rock, dust, ice and frozen gases such as carbon monoxide, carbon dioxide, methane, and ammonia. Sometimes called dirty snowballs, recent studies have shown that the ice of a comet is covered by a crust. Comets also contain a variety of organic compounds as well as the gases already mentioned. Some of these are methanol, hydrogen cyanide, formaldehyde, ethanol, and ethane. More complex molecules such as long-chain hydrocarbons and amino acids may also be in comets. Because of their low mass, comets cannot become spherical under their own gravity, and will thus have irregular shapes. Comets do not zip through the sky like meteors, they do noticeable move across the sky in a matter of minutes or even hours. The speed of a comet is on average, roughly 20,000 mph. It is believed that about every 130 million years a comet or a large asteroid hits earth and wipes out life itself. Comets are believed to come from two sources. One is the “Oort Cloud”. Those which take more than 200 years to complete an orbit around the sun originate from the “Oort Cloud. Comets that take less than 200 years to orbit around the sun come from the Kuiper Belt.
Asteroid: Asteroids are small solar system bodies that orbit the Sun. Made of rock and metal, they can also contain organic compounds. Asteroids are similar to comets but do not have a visible coma (fuzzy outline and tail) like comets do. The asteroids that are nearest the Sun are mostly made of carbon while the ones further away are made up of silicate rock. The metallic asteroids are composed of up to 80% iron and 20% a mixture of nickel, iridium, palladium, platinum, gold, and other precious metals. Although most asteroids revolve within the Asteroid Belt, a few asteroids have eccentric orbits that wander outside the region between Mars and Jupiter. Some asteroids even cross Earth's orbit. The unusually eccentric orbits of these asteroids are a result of collisions in the Asteroid Belt that sent asteroids on a new path. An asteroid has an average orbital speed (how fast an object orbits the sun) of 25 kilometers per second. However, asteroids orbiting closer to a sun will move faster than asteroids orbiting between Mars and Jupiter and beyond. Asteroids that are roughly 5-10 meters in diameter will strike earth once a year. Asteroids that are about 50 meters in diameter will strike earth about every 1000 years. Asteroids with the diameter of about 1 km will hit the earth every 500,000 years. Diameters greater than 5 km will approximately hit the earth every 10 million years. Most of them are grouped in the main belt, but that is not the only asteroid field in the solar system. There are actually four sets of asteroids grouped into different fields: the main belt, Trojans, scattered disc, and the Kuiper belt. Most scientists agree that all of the asteroids are the result of the the big bang. After the initial turmoil, large asteroids collided together and through the process known as accretion planets and dwarf planets were formed. The planets and dwarfs grew large enough to develop gravity and became rounded and able to sustain their own gravity. Asteroids continued to collide and destroy each other until we have the elliptical and other odd shaped, pock-marked solar objects that we have today. The largest known asteroid in the belt is Ceres which accounts for 27% of the belts’ total mass. Ceres is also the only asteroid in the belt that is classified as a dwarf planet.
Meteor: A meteoroid that burns up as it passes through the Earth’s atmosphere is known as a meteor. If you’ve ever looked up at the sky at night and seen a streak of light or ‘shooting star’ what you are…