We began our journey through the Solar System exploring the planets. We discovered that they follow certain rules. These rules say that the inner planets are small and dense while the outer planets are large and gaseous. We discovered that planets in the same part of the Solar System are alike, such as Earth and Venus, or Uranus and Neptune.
Studying the planets does not, however, conclude our journey. There are other things, other very exciting things still to explore in the Solar System. In this astronomy packet we are going to discuss the Asteroid Belt where asteroids come from, and the Kuiper Belt and Oort cloud where comets come from. We will then learn about the moons of our Solar System.
The Asteroid Belt:
If you traveled towards the planet Jupiter, along your way you would have to fly though an area called the Asteroid Belt. The Asteroid Belt sits between the planets Mars and Jupiter. It is a region of space where millions of rocks can be found circling the Sun. Some of these rocks are very big, like Ceres which is over 500 miles long. Others are as small as a baseball. But most are medium size, about the size of your house.
Are asteroids only found in the Asteroid Belt?
This is an important question to think about. As long as asteroids remain in the Asteroid Belt they can not harm the Earth. It is the ones which stray from the belt which worry us. Unfortunately, not all asteroids are found in the asteroid belt. It is believed that at least 5000 asteroids have an orbit which leaves the asteroid belt, and brings them towards the Earth. Don’t worry, the really big ones only hit the Earth about every 100 million years.
The Kuiper Belt:
Many of us have heard of the Asteroid Belt, but far less know about another belt in the Solar System called the Kuiper Belt. The Kuiper belt lies out past the orbit of Pluto. Instead of Asteroids, this belt has millions of icy comets which circle the Sun very fast. Last week we learned that many scientists think Pluto is a comet or a dwarf planet. They think it is actually part of the Kuiper belt.
It is believed that as the Solar System formed billions of years ago, trillions of these comets were formed all around the Solar System. Most of the comets which used to be in the inner Solar System have either crashed into the moons and planets, or been thrown out by the powerful gravity of Jupiter and Saturn. Over billions of years most of the comets have been cleaned out of the inner Solar System.
The comets of the Kuiper belt do not have to worry about large planets, because there are none that far out. They also do not have to worry about crashing into planets or moons. This means that they have been left alone, free to orbit the Sun in peace.
The comets in the Kuiper Belt and the asteroids in the Asteroid Belt all circle the Sun on the same plane as the planets. Think of a spinning record. Just like a flat record, everything we have talked about in the Solar System so far spins on a flat disk, and in the same direction.
The Oort Cloud:
The Oort Cloud is not really a cloud. It is a mass of a trillion or so comets which circle the Sun at a great distance. The Oort Cloud extends 13,950,000,000,000 miles from the Sun.
Unlike the Kuiper Belt, the comets in the Oort Cloud circle the Sun in every direction. They do not stay on the flat disk. These objects break the rules of the Solar System and create a sphere of comets around the Sun.
It is believed that the Oort cloud formed as trillions of comets where thrown out of the inner Solar System by Jupiter and Saturn. In other words, the comets of the Oort cloud actually formed in the inner Solar System, but were then flung out almost as if Jupiter and Saturn were giant sling shots.
Assignment # 1:
What is the difference between the Kuiper Belt and the Oort Cloud?