Asteroids,Comets and Meteorites


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Asteroids,Comets and Meteorites

  1. 1. What are asteroids? An asteroid is a large rock in outer space. Some, like Ceres, can be very large, while others are as small as a grain of sand. Due to their smaller size, asteroids do not have enough gravity to pull themselves into the shape of a ball.  Astronomers group asteroids into different categories based on the way they reflect sunlight. The asteroid belt is divided into an inner belt and an outer belt. The inner belt, which is made up of asteroids that are within 250 million miles (402 million km) of the Sun, contains asteroids that are made of metals. The outer belt, which includes asteroids 250 million miles (402 million km) beyond the Sun, consists of rocky asteroids. These asteroids
  2. 2. Asteroids are left over materials from the formation of the Solar System.  These materials were never incorporated into a planet because of their proximity to Jupiter's strong gravity. How many asteroids are there? 26 very large asteroids have been discovered, which is probably most of the big ones. But there are still millions of smaller ones that we have yet to see because they are too tiny, only a mile or so across. If we stuck all the asteroids together, how big would the new planet be? If all the materials of all the asteroids were squashed up into one planet it would be smaller than our moon.
  3. 3. While most asteroids can be found in the Asteroid Belt, others are in strange orbits straying far from home. It is currently believed that at least 5000 asteroids cross the Earth's orbit, some coming very close. Don't worry though, asteroids and comets only hit the Earth every 100 million years or so.
  4. 4. What  are comets? A comet is a small world which scientists sometimes call a planetesimal. They are made out of dust and ice, kind of like a dirty snow ball. Where do they come from? Comets come from two places:  The Kuiper Belt and the Oort Cloud.  Imagine a place far, far away at the very edge of the Solar System. A place where millions of comets can be seen swishing around in every direction. These icy comets are orbiting the Sun in two different places, both of which are very distant.  One place is called the Oort cloud, and the other is called the Kuiper Belt.
  5. 5. Many people think that a comet's tail is always following behind it, but actually the coma, or tail, can either be behind the comet or in front of it. Which way the tail is pointing depends on where the Sun . That's right, the Sun's heat and radiation produce a wind called the Solar Wind , as a comet gets close to the Sun it begins to melt. The gas and dust that melt off are blown away from the Sun by the solar winds. So if a comet is traveling towards the Sun then the tail will follow behind, but if the comet is traveling away from the Sun the tail will be in front of the comet.
  6. 6. What meteorites are and where they come from? Meteorites are chunks of rocks or metal that fall from space. They are named after the place they are found. Most meteorites are very small but they can be huge and weigh more than a car. Where in space are they from? Most meteorites come from the asteroid belt. This is a region between Mars and Jupiter that contains many rock fragments broken off from asteroids. There are 31,000 meteorites that we know about and all but 139 came from here.
  7. 7. Non-asteroid meteorites A small number of meteorites are made from particles from other planets. They are known as non-asteroid meteorites. Some of these come from Mars. Scientists know this because small fragments of glass in these meteorites contain particles of atmosphere from the planet it came from. Martian meteorites are not as old as those from the asteroid belt. A small number of non-asteroid meteorites come from the moon. They were broken off when asteroids and comets hit the surface.
  8. 8. . Some people claim they have been hit by meteorites as they fall from the sky. This is extremely rare and many cases are unproven. The first human we know to be hit by a meteorite is Ann Hodges who lived in Alabama, USA. In 1954, a meteorite crashed through her ceiling and struck her after bouncing off her radio. She was badly bruised and had a lucky escape as the meteorite weighed 4kg, about the same as a domestic cat. The oldest report is from 1911 in Egypt when a dog was said to have been killed by a Martian meteorite. The Barwell meteorite was the biggest to fall over Britain. It broke up and fell as a shower of stones over the Leicestershire village of Barwell on Christmas eve, 1965. The Barwell meteorite, the biggest meteorite to fall on Britain.
  9. 9. What is the difference between an asteroid, comet, meteoroid, meteor and meteorite? Asteroid: A relatively small, inactive body, composed of rock, carbon or metal, which is orbiting the Sun. Comet:   relatively small, sometimes active A object, which is composed of dirt and ices. Comets are characterized by dust and gas tails when in proximity to the Sun. Far from the Sun it is difficult to distinguish an asteroid Meteoroid: from a comet. A small particle from an asteroid or   comet orbiting he Sun. Meteor: burns up in the Earth's atmosphere -   A meteoroid that is observed as it a shooting star.   meteoroid that survives its passage A