Our home in space


Imagine yourself on a roundabout spinning at 10,400 kilometres an hour. That is the speed of the Earth as it goes round the Sun.
This picture shows all of the planets. Each one is on a solar roundabout that moves at its own speed. Some of the planets also have moons going around them.
The Earth and all the other planets go around the Sun because of gravity. The force of gravity between the Sun and the planets stops the planets from flying off into space.
The Earth and the other eight planets are not the only things that go around the Sun. There is also a ring of small rocky objects orbiting the Sun. These lumps of rock are called asteroids. There are also comets which form long tails when they are near the Sun.

What is the Solar System?
It is the Sun, which is a star, the nine planets, the moons of the planets, the asteroids and the comets and everything that moves round it.
The Solar System is in the Milky Way Galaxy. This is a group of 500,000 million stars.

From space, the Milky Way Galaxy looks like a catherine wheel at a firework display. From the Earth, we see part of it as a band of stars in the night sky.
The Solar System is about half-way between the centre of the galaxy and its edge. The Milky Way Galaxy is just one of the 100,000 million galaxies in the Universe.

Where did the Solar System come from?
Thirteen billion years ago there were no stars or planets. Suddenly, and for a reason no one yet knows, the Universe began from a single speck, growing at a fantastic rate.
Very soon it had grown to the size of hundreds of galaxies.
This explosive growth was called the Big Bang, and it was here that the first materials formed. They were two gases called hydrogen and helium. In time the two gases swirled together and formed glowing globes – the stars. Inside the stars hydrogen and helium fused together to make more materials and when the stars exploded or simply faded away the materials were thrown out into space to form cosmic dust.
About five billion years ago a region of cloud of gas and dust was sent in a spin by an exploding star. As the gas and dust swirled around, it formed the Solar System. Hydrogen and helium gases formed the Sun, while the dust formed the planets, the moons and asteroids. More gases were drawn towards the four largest planets, giving them enormously thick atmospheres and turning them into the giants we see today.

What will happen to the Solar System?
Inside the Sun hydrogen is turned to helium. This makes the Sun shine and gives out heat. In about five billion years the Sun will have used up all its hydrogen. As this happens, it will swell up to form a large red star and swallow up Mercury and Venus. Earth and Mars will be baked and large planets will have their gases blown away. The Sun will then collapse and form a dim white star with the remains of the planets going around it.
If people are still living on Earth when these changes begin, they will have to build starships, leave the Earth before it is destroyed by the Sun, and look for planets around other stars where they can set up home.

Where have humans been in the Solar System?
Humans have sent probes to several planets, comets and other parts of the Solar System, but have only ever set foot on the Moon, the closest object to Earth. The first visit to the Moon was in 1969. Neil Armstrong was the first person to set foot on the Moon.
The project to put people on the Moon was called the Apollo Space project. There were 17 Apollo missions. In each one a spacecraft was launched but not all went to the Moon. In some missions the astronauts tested equipment and returned to Earth. The first mission to take astronauts to the Moon was called Apollo 11. The two astronauts who landed on the Moon at that time were Neil Armstrong and Edwin 'Buzz' Aldrin. The last Apollo mission was called Apollo 17 and took place in 1972. The astronauts who visited the Moon at that tome were Eugene A. Cernan, Ronald E. Evans and Harrison Schmitt.