The Solar System is our home and in this series, I plan to discuss the Solar System in detail. In this post, I’m going to start with a general overview of the structure of the Solar System and then follow with a more detailed post about the Sun, each of the planets, minor planets and other objects that make up the Solar System. At the centre of the Solar System is the Sun. The Sun is a star and is where we get all our energy.
All of the objects in the Solar System orbit the Sun. To orbit the Sun means that the object travels around the Sun in a shape called an ellipse. An ellipse is a slightly stretched circle. Each planet takes a different amount of time to complete an orbit around the Sun. For Earth, this is 365 days (approximately), which is why there are 365 days in a year.
The structure of the Solar System is as follows;
Starting our journey at the Sun, first come the rocky planets; Mercury, Venus, Earth and Mars. Mercury is closest to the Sun. It has very little atmosphere and has very large temperature differences between daylight areas and night time areas. The next planet out is Venus. Venus is often refereed to as Earth’s Evil Twin as it is similar to Earth in some ways but the conditions are extremely harsh with severe heat and pressure. The third planet is our home, Earth. The last of the rocky planets is Mars. Mars has a thin atmosphere and is one of the most explored planets in the Solar System.
Next we have a region know as the asteroid belt. The asteroid belt is thought to be some of the left overs from the formation of the Solar System. It is made up of small pieces of rock and ice. Some of the pieces are tiny and others are hundreds of kilometres in size. The minor planet, Ceres, is the largest object in the asteroid belt at 473 km across. Despite there being millions of objects in the asteroid belt, they are so far apart. Spacecraft regularly pass through it without worrying about colliding with anything.
After we pass the asteroid belt on our journey, we then reach the large gas planets. These are Jupiter, Saturn, Uranus and Neptune. Jupiter is the largest of all the planets and has a storm called the Great Red Spot which is 1.3 times the diameter of Earth which has been raging for at least 360 years. Saturn is probably most famous for it’s beautiful ring system. Next is Uranus, a green colored planet which is different to the rest in that it is tilted on it’s side. The eighth and last planet is Neptune. It is a blue planet and has violent winds that can reach 2,200 km/h.
Once we pass Neptune, we are now in the trans-Neptunian region. It is here we find the Kuiper belt. The Kuiper belt is similar to the asteroid belt but most of its objects are made of ice. The Kuiper belt is where you find the minor planet Pluto. The edge of the Solar System is where the effect of the solar wind stops and this is called the heliopause. There have only been 2 spacecraft that have reached the heliopause, Voyager 1 and Voyager 2. Voyager 1 passed the heliopause and left the Solar System on 25th August 2012, 35 years after being launched from Earth in 1977. At that time the spacecraft was so far away that it took sunlight nearly 17 hours to reach it. This really goes to show the vastness of space.
I’ll end this with one of the only family portraits we have of the Solar System. On 14th February Voyager 1 turned its camera back and took this photo of the Solar System from 4 billion miles away. Like most family portraits though, there are 2 of the 8 planets missing. Unfortunately, Mercury is too close to the Sun to make out in the photo and Mars was in the wrong part of its orbit to be seen in the photo.
Paul Smith 