Asteroid and Comets

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For many years comets and asteroids remained hidden to the world. The first of them weren’t discovered until the 19th century. The reason why discovering the asteroids and comets took so long was because proper technology was needed to observe such faraway items. Comets and asteroids are often thought of as the same thing when they are in fact very different from one another.

Asteroids, also known as minor planets or planetoids can measure any size. The smallest Asteroid to ever be found had a diameter of 20 feet, while the largest found had a diameter of 580 miles. Some bigger asteroids even have moons orbiting them. Ceres is the largest asteroid found in the main asteroid belt between the orbits of Mars and Jupiter. It measures about 975 km, and in 2006 it was classified as a dwarf planet. It contains almost a third of the belt’s total mass by itself. One day on Ceres is 9 hours. Asteroids can have round or irregular shapes. They also vary in composition, but are usually made out of rocks, nickel, and minerals. Some also contain iron and carbon. There are three different types of asteroids. The m-type which is the brightest because it reflects the sunlight, makes up the smallest portion of known asteroids. That is only 8%. The c-type, which is the darkest because it is made of mostly iron and carbon, and doesn’t reflect the sunlight very well, make up 75% of the astero ids we know. The s-type which contain silicate and are only found in the inner part of the asteroid belt, make up 17 % of know asteroids. The average temperature on asteroids is -100 degrees Fahrenheit or -73 degrees Celsius. Most asteroids can be found in an asteroid belt between Mars and Jupiter were they orbit the sun. Millions of asteroids have been found there. Most asteroids follow elliptical orbits, which are oval shaped. If an asteroid has a close encounter with Mars or Jupiter, it can be pushed into another planets orbit. When this happens asteroids are some times broken into smaller pieces or they collide with another planet. Some scientists believe this happened on Earth 65 million years ago, which led to many climate changes and the eventual extinction of dinosaurs. Occasionally, asteroids hit Earth. If an asteroid doesn’t burn before it touches the ground, it is called a meteorite. From all meteorites found, 92.8% are composed of silicate, 5.7% are composed of iron and nickel, and the rest are composed of different minerals. There are many different theory’s of how asteroids were created, but the mostly accepted one is that they left over remains from when the solar system was created 4.6 billion years ago. Most scientists believe that the solar system formed from a Nebula of gas, dust and ices, that turned into a disk around the developing sun. Inside it, there were tiny dust grains that coagulated and eventually became planets. Between Mars and Jupiter, no rocks ever turned into pl anets because of Jupiter’s very strong gravitational pull. Other asteroids combined together to form what are now planets and satellites. When asteroids have similar orbital elements, they are named after the astronomer Kiyotsogu Hirayama because he was the first one to recognize that the families existed.
Comets are icy body’s that release gas or dust. They contain rock, dust, ice, and frozen gases. Although their ice is made of water, it can contain other substances like ammonia, carbon dioxide, carbon monoxide, and methane. Their core is a solid nucleus (ball of ice and rocky particles) that’s surrounded by a cloudy atmosphere called a coma. Comas can have two or three tails. Comets orbit the sun, and when they are close enough to the sun, the gas and dust from their tails reflects sunlight so you can see their tails behind them. These tails can be up to ten million kilometers long. The tail is the easiest part of a comet to see without any visual aid. As comets get near the inner solar system, the heat from the evaporates some of the nucleus, which sometimes causes it to breakdown. When this happens, gas and dust are spewed everywhere, and they combine with more dust and gases to form new comet. Comets measure anywhere from 100 meters to 40 km across. Although most comets are to small or faint to be seen from Earth without a telescope, only comets traveling around the sun in large, oval orbits can be seen from Earth. Like asteroids comets are separated into different groups. There are two groups. The first one is short period comets, they take 200 years or less to orbit the sun. The second group is long period comets, they take 200 year or more to orbit the sun. Some Comets have very large orbits that go far beyond Pluto, and they cant take millenniums to come back into the inner solar system. Some comets have been found to take over thirty million years to complete one orbit around the sun. The most famous of short period comets is comet Halley. This comet can be seen every 75-76 years. Halley is so famous because it has been Observed since 240 BC. The reason why there are so many records of it is because it is the only shot period comet that can easily be seen with the naked eye. Scientists believe that short period comets come from a set of objects called the kupid belt, which is located a bit farther than Pluto’s orbit. Large outer planets with strong gravitational pulls can pull these comets into the inner solar system. Long period comets come from a place much farther away called the Oort cloud. The Oort cloud is about one light year, or 1000 times farther away from the sun than Pluto’s orbit. This is why Comets are so icy. They are very far from our sun, and almost no heat reaches them. When passing stars have strong enough gravitational pulls, they can pull comets into the inner solar system. Every time comets come into the inner solar system, they loose ice and dust. Eventually they loose all their ice and dust, and breakup or displa ce into clouds. The dust can also turn into smaller inactive objects similar to asteroids. When comets loose dust and ice, and cross Earth’s path, we can see meteor showers. Comets can also come into close encounters with other planets, and fall into new orbits, or be expelled from the solar system. This especially happens with Jupiter because Comets aren’t as much a threat to Earth as asteroids are, because of their quantity and distance from Earth, but in 1994 the comet Shomaker-Levy 9 broke into pieces and collided with Jupiter. If this had happened to Earth, there would have been disastrous consequences. Scientists believe that about 4 billion years ago Earth was constantly being bombarded by comets. Some scientists believe that these comets brought a large portion of water, and some even believe that comets brought life on Earth. If this is true, comets may be a source for future resources. There have been some attempts to study comets. In 2004 Nasa’s stardust mission visited the comet wild 2, and in 2006 took a sample of comet particles back to Earth.